The GDBN remote serial protocol
-------------------------------

To debug a program running on another machine (the debugging target machine), you must first arrange for all the usual prerequisites for the program to run by itself.  For example, for a C program, you need:

 1. A startup routine to set up the C runtime environment; these usually have a name like crt0.  The startup routine may be supplied by your hardware supplier, or you may have to write your own.

 2. You probably need a C subroutine library to support your program's subroutine calls, notably managing input and output.

 3. A way of getting your program to the other machine---for example, a download program.  These are often supplied by the hardware manufacturer, but you may have to write your own from hardware documentation.

The next step is to arrange for your program to use a serial port to communicate with the machine where GDBN is running (the host machine).  In general terms, the scheme looks like this:

On the host,
     GDBN already understands how to use this protocol; when everything else is set up, you can simply use the target remote command (see Specifying a Debugging Target).

On the target,
     you must link with your program a few special-purpose subroutines that implement the GDBN remote serial protocol.  The file containing these subroutines is called  a debugging stub.

     On certain remote targets, you can use an auxiliary program gdbserver instead of linking a stub into your program. See Using the gdbserver program, for details.

The debugging stub is specific to the architecture of the remote machine; for example, use sparc-stub.c to debug programs on SPARC boards.

These working remote stubs are distributed with GDBN:

i386-stub.c
     For Intel 386 and compatible architectures.

m68k-stub.c
     For Motorola 680x0 architectures.

sh-stub.c
     For Hitachi SH architectures.

sparc-stub.c
     For SPARC architectures.

sparcl-stub.c
     For Fujitsu SPARCLITE architectures.

The README file in the GDBN distribution may list other recently added stubs.

What the stub can do for you
............................

The debugging stub for your architecture supplies these three subroutines:

set_debug_traps
     This routine arranges for handle_exception to run when your program stops.  You must call this subroutine explicitly near the beginning of your program.

handle_exception
     This is the central workhorse, but your program never calls it explicitly---the setup code arranges for handle_exception to run when a trap is triggered.

     handle_exception takes control when your program stops during execution (for example, on a breakpoint), and mediates communications with GDBN on the host machine.  This is where the communications protocol is implemented; handle_exception acts as the GDBN representative on the target machine; it begins by sending summary information on the state of your program, then continues to execute, retrieving and transmitting any information GDBN needs, until you execute a GDBN command that makes your program resume; at that point, handle_exception returns control to your own code on the target machine.

breakpoint
     Use this auxiliary subroutine to make your program contain a breakpoint.  Depending on the particular situation, this may be the only way for GDBN to get control.  For instance, if your target machine has some sort of interrupt button, you won't need to call this; pressing the interrupt button transfers control to handle_exception---in effect, to GDBN.  On some machines, simply receiving characters on the serial port may also trigger a trap; again, in that situation, you don't need to call breakpoint from your own program---simply running target remote from the host GDBN session gets control.

     Call breakpoint if none of these is true, or if you simply want to make certain your program stops at a predetermined point for the start of your debugging session.

What you must do for the stub
.............................

The debugging stubs that come with GDBN are set up for a particular chip architecture, but they have no information about the rest of your debugging target machine.

First of all you need to tell the stub how to communicate with the serial port.

int getDebugChar()
     Write this subroutine to read a single character from the serial port. It may be identical to getchar for your target system; a different name is used to allow you to distinguish the two if you wish.

void putDebugChar(int)
     Write this subroutine to write a single character to the serial port. It may be identical to putchar for your target system; a different name is used to allow you to distinguish the two if you wish.

If you want GDBN to be able to stop your program while it is running, you need to use an interrupt-driven serial driver, and arrange for it to stop when it receives a ^C (\003, the control-C character).  That is the character which GDBN uses to tell the remote system to stop.

Getting the debugging target to return the proper status to GDBN probably requires changes to the standard stub; one quick and dirty way is to just execute a breakpoint instruction (the ``dirty'' part is that GDBN reports a SIGTRAP instead of a SIGINT).

Other routines you need to supply are:

void exceptionHandler (int EXCEPTION_NUMBER, void *EXCEPTION_ADDRESS)
     Write this function to install EXCEPTION_ADDRESS in the exception handling tables.  You need to do this because the stub does not have any way of knowing what the exception handling tables on your target system are like (for example, the processor's table might be in ROM, containing entries which point to a table in RAM). EXCEPTION_NUMBER is the exception number which should be changed; its meaning is architecture-dependent (for example, different numbers might represent divide by zero, misaligned access, etc).  When this exception occurs, control should be transferred directly to EXCEPTION_ADDRESS, and the processor state (stack, registers, and so on) should be just as it is when a processor exception occurs.  So if you want to use a jump instruction to reach EXCEPTION_ADDRESS, it should be a simple jump, not a jump to subroutine.

     For the 386, EXCEPTION_ADDRESS should be installed as an interrupt gate so that interrupts are masked while the handler runs.  The gate should be at privilege level 0 (the most privileged level).  The SPARC and 68k stubs are able to mask interrupts themselves without help from exceptionHandler.

void flush_i_cache()
     (sparc and sparclite only) Write this subroutine to flush the instruction cache, if any, on your target machine.  If there is no instruction cache, this subroutine may be a no-op.

     On target machines that have instruction caches, GDBN requires this function to make certain that the state of your program is stable.

You must also make sure this library routine is available:

void *memset(void *, int, int)
     This is the standard library function memset that sets an area of memory to a known value.  If you have one of the free versions of libc.a, memset can be found there; otherwise, you must either obtain it from your hardware manufacturer, or write your own.

If you do not use the GNU C compiler, you may need other standard library subroutines as well; this varies from one stub to another, but in general the stubs are likely to use any of the common library subroutines which gcc generates as inline code.

Putting it all together
.......................

In summary, when your program is ready to debug, you must follow these steps.

 1. Make sure you have the supporting low-level routines (see What you must do for the stub):

          getDebugChar, putDebugChar,
          flush_i_cache, memset, exceptionHandler.

 2. Insert these lines near the top of your program:

          set_debug_traps();
          breakpoint();

 3. For the 680x0 stub only, you need to provide a variable called exceptionHook.  Normally you just use:

          void (*exceptionHook)() = 0;

     but if before calling set_debug_traps, you set it to point to a function in your program, that function is called when GDBN continues after stopping on a trap (for example, bus error).  The function indicated by exceptionHook is called with one parameter: an int which is the exception number.

 4. Compile and link together: your program, the GDBN debugging stub for your target architecture, and the supporting subroutines.

 5. Make sure you have a serial connection between your target machine and the GDBN host, and identify the serial port on the host.

 6. Download your program to your target machine (or get it there by whatever means the manufacturer provides), and start it.

 7. To start remote debugging, run GDBN on the host machine, and specify as an executable file the program that is running in the remote machine. This tells GDBN how to find your program's symbols and the contents of its pure text.

     Then establish communication using the target remote command. Its argument specifies how to communicate with the target machine---either via a devicename attached to a direct serial line, or a TCP port (usually to a terminal server which in turn has a serial line to the target).  For example, to use a serial line connected to the device named /dev/ttyb:

          target remote /dev/ttyb

     To use a TCP connection, use an argument of the form HOST:port.  For example, to connect to port 2828 on a terminal server named manyfarms:

          target remote manyfarms:2828

Now you can use all the usual commands to examine and change data and to step and continue the remote program.

To resume the remote program and stop debugging it, use the detach command.

Whenever GDBN is waiting for the remote program, if you type the interrupt character (often C-C), GDBN attempts to stop the program.  This may or may not succeed, depending in part on the hardware and the serial drivers the remote system uses.  If you type the interrupt character once again, GDBN displays this prompt:

     Interrupted while waiting for the program.
     Give up (and stop debugging it)?  (y or n)

If you type y, GDBN abandons the remote debugging session. (If you decide you want to try again later, you can use target
remote again to connect once more.)  If you type n, GDBN goes back to waiting.

Communication protocol
......................

The stub files provided with GDBN implement the target side of the communication protocol, and the GDBN side is implemented in the GDBN source file remote.c.  Normally, you can simply allow these subroutines to communicate, and ignore the details.  (If you're implementing your own stub file, you can still ignore the details: start with one of the existing stub files.  sparc-stub.c is the best organized, and therefore the easiest to read.)

However, there may be occasions when you need to know something about the protocol---for example, if there is only one serial port to your target machine, you might want your program to do something special if it recognizes a packet meant for GDBN.

In the examples below, <- and -> are used to indicate transmitted and received data respectfully.

All GDBN commands and responses (other than acknowledgments) are sent as a PACKET.  A PACKET is introduced with the character $, this is followed by an optional two-digit SEQUENCE-ID and the character :, the actual PACKET-DATA, and the terminating character # followed by a two-digit CHECKSUM:

     $PACKET-DATA#CHECKSUM

or, with the optional SEQUENCE-ID:

     $SEQUENCE-ID:PACKET-DATA#CHECKSUM

The two-digit CHECKSUM is computed as the modulo 256 sum of all characters between the leading $ and the trailing # (that consisting of both the optional SEQUENCE-ID: and the actual PACKET-DATA).

The two-digit SEQUENCE-ID, when present, is returned with the acknowledgment.  Beyond that its meaning is poorly defined. GDBN is not known to output SEQUENCE-IDs.

When either the host or the target machine receives a packet, the first response expected is an acknowledgment: either + (to indicate the package was received correctly) or - (to request retransmission):

     <- $PACKET-DATA#CHECKSUM
     -> +

If the received packet included a SEQUENCE-ID than that is appended to a positive acknowledgment:

     <- $SEQUENCE-ID:PACKET-DATA#CHECKSUM
     -> +SEQUENCE-ID

The host (GDBN) sends COMMANDs, and the target (the debugging stub incorporated in your program) sends a RESPONSE.  In the case of step and continue COMMANDs, the response is only sent when the operation has completed (the target has again stopped).

PACKET-DATA consists of a sequence of characters with the exception of # and $ (see X packet for an exception). : can not appear as the third character in a packet. Fields within the packet should be separated using , and ; (unfortunately some packets chose to use :).  Except where otherwise noted all numbers are represented in HEX with leading zeros suppressed.

Response DATA can be run-length encoded to save space.  A * means that the next character is an ASCII encoding giving a repeat count which stands for that many repetitions of the character preceding the *.  The encoding is n+29, yielding a printable character where n >=3 (which is where rle starts to win).  Don't use an n > 126.

So:

     "0* "

means the same as "0000".

The error response, returned for some packets includes a two character error number.  That number is not well defined.

For any COMMAND not supported by the stub, an empty response ($#00) should be returned.  That way it is possible to extend the protocol.  A newer GDBN can tell if a packet is supported based on the response.

Below is a complete list of all currently defined COMMANDs and their corresponding response DATA:

Packet
Request
Description

extended ops (optional)
!

Use the extended remote protocol. Sticky -- only needs to be set once.
The extended remote protocol support the R packet.

reply

Stubs that support the extended remote protocol return which,
unfortunately, is identical to the response returned by stubs that do not
support protocol extensions.

last signal
?

Reply the current reason for stopping.  This is the same reply as is
generated for step or cont : SAA where AA is the
signal number.

reserved
a
Reserved for future use

set program arguments (reserved) (optional)
AARGLEN,ARGNUM,ARG,...

Initialized argv[] array passed into program. ARGLEN
specifies the number of bytes in the hex encoded byte stream ARG.

reply OK

reply ENN

set baud (deprecated)
bBAUD

Change the serial line speed to BAUD.  JTC: When does the
transport layer state change?  When it's received, or after the ACK is
transmitted.  In either case, there are problems if the command or the
acknowledgment packet is dropped. Stan: If people really wanted
to add something like this, and get it working for the first time, they
ought to modify ser-unix.c to send some kind of out-of-band message to a
specially-setup stub and have the switch happen "in between" packets, so
that from remote protocol's point of view, nothing actually
happened.

set breakpoint (deprecated)
BADDR,MODE

Set (MODE is S) or clear (MODE is C) a
breakpoint at ADDR.  This has been replaced by the Z and
z packets.

continue
cADDR

ADDR is address to resume. If ADDR is omitted, resume at
current address.

reply
see below

continue with signal (optional)
CSIG;ADDR

Continue with signal SIG (hex signal number).  If
;ADDR is omitted, resume at same address.

reply
see below

toggle debug (optional)
d

toggle debug flag (see 386 & 68k stubs)

detach (optional)
D
Reply OK.

reserved
e
Reserved for future use

reserved
E
Reserved for future use

reserved
f
Reserved for future use

reserved
F
Reserved for future use

read registers
g
Read general registers.

reply XX...

Each byte of register data is described by two hex digits.  The bytes
with the register are transmitted in target byte order.  The size of
each register and their position within the g PACKET is
determined by the REGISTER_RAW_SIZE and REGISTER_NAME
macros.

ENN
for an error.

write regs
GXX...

See g for a description of the XX... data.

reply OK
for success

reply ENN
for an error

reserved
h
Reserved for future use

set thread (optional)
HCT...

Set thread for subsequent operations.  C = c for thread
used in step and continue; T... can be -1 for all threads.
C = g for thread used in other operations.  If zero, pick a
thread, any thread.

reply OK
for success

reply ENN
for an error

cycle step (draft) (optional)
iADDR,NNN

Step the remote target by a single clock cycle.  If ,NNN is
present, cycle step NNN cycles.  If ADDR is present, cycle
step starting at that address.

signal then cycle step (reserved) (optional)
I

See i and S for likely syntax and semantics.

reserved
j
Reserved for future use

reserved
J
Reserved for future use

kill request (optional)
k

reserved
l
Reserved for future use

reserved
L
Reserved for future use

read memory
mADDR,LENGTH

Read LENGTH bytes of memory starting at address ADDR.

reply XX...

XX... is mem contents. Can be fewer bytes than requested if able to
read only part of the data.

reply ENN
NN is errno

write mem
MADDR,LENGTH:XX...

Write LENGTH bytes of memory starting at address ADDR.
XX... is the data.

reply OK
for success

reply ENN

for an error (this includes the case where only part of the data was
written).

reserved
n
Reserved for future use

reserved
N
Reserved for future use

reserved
o
Reserved for future use

reserved
O
Reserved for future use

read reg (reserved)
pN...

See write register.

return R....
The hex encoded value of the register in target byte order.

write reg (optional)
PN...=R...

Write register N... with value R..., which contains two hex
digits for each byte in the register (target byte order).

reply OK
for success

reply ENN
for an error

general query (optional)
qQUERY

Request info about QUERY. In general GDBN QUERY's
have a leading upper case letter.  Custom vendor queries should use a
leading lower case letter and a company prefix, ex: qfsf.var.
QUERY may optionally be followed by a , or ;
separated list.  Stubs should ensure that they fully match any
QUERY name.

reply XX...
Hex encoded data from query. The reply can not be empty.

reply ENN
error reply

reply
Indicating an unrecognized QUERY.

current thread
qC
Return the current thread id.

reply QCPID

Where PID is a HEX encoded 16 bit process id.

reply *
Any other reply implies the old pid.

compute CRC of memory block
qCRC:ADDR,LENGTH

reply ENN
An error (such as memory fault)

reply CCRC32
A 32 bit cyclic redundancy check of the specified memory region.

query LIST or THREADLIST
qLSTARTFLAGTHREADCOUNTNEXTTHREAD

Obtain thread information from RTOS.  STARTFLAG is one hex digit;
THREADCOUNT is two hex digits; and NEXTTHREAD is 16 hex
digits.

reply *

See remote.c:parse_threadlist_response().

query sect offs
qOffsets
Get section offsets.

reply Text=XXX;Data=YYY;Bss=ZZZ

thread info request
qPMODETHREADID

Returns information on THREADID.  Where: MODE is a hex
encoded 32 bit mode; THREADID is a hex encoded 64 bit thread ID.

reply *

See remote.c:remote_unpack_thread_info_response().

remote command (reserved)
qRcmd,COMMAND

COMMAND (hex encoded) is passed to the local interpreter for
execution.  Implementors should note that providing access to a
stubs's interpreter may have security implications.

reply OUTPUT

The OUTPUT (hex encoded).  Must be non-empty.

reply

When qRcmd is not recognized.

general set (optional)
QVAR=VAL

Set value of VAR to VAL.  See q for a discussing of
naming conventions.

reset (optional)
r
reset -- see sparc stub.

remote restart (optional)
RXX

Restart the remote server. XX while needed has no clear
definition.

step (optional)
sADDR

ADDR is address to resume.  If ADDR is omitted, resume at
same address.

reply
see below

step with signal (optional)
SSIG;ADDR

Like C but step not continue.

reply
see below

search (optional)
tADDR:PP,MM

Search backwards starting at address ADDR for a match with pattern
PP and mask MM.  PP and MM are 4
bytes. ADDR must be at least 3 digits.

thread alive (optional)
TXX
Find out if the thread XX is alive.

reply OK
thread is still alive

reply ENN
thread is dead

reserved
u
Reserved for future use

reserved
U
Reserved for future use

reserved
v
Reserved for future use

reserved
V
Reserved for future use

reserved
w
Reserved for future use

reserved
W
Reserved for future use

reserved
x
Reserved for future use

write mem (binary) (optional)
XADDR,LENGTH:XX...

ADDR is address, LENGTH is number of bytes, XX... is
binary data.

reply OK
for success

reply ENN
for an error

reserved
y
Reserved for future use

reserved
Y
Reserved for future use

remove break or watchpoint (draft) (optional)
zT,ADDR,LENGTH

See Z.

insert break or watchpoint (draft) (optional)
ZT,ADDR,LENGTH

T is type: 0 - software breakpoint, 1 - hardware
breakpoint, 2 - write watchpoint, 3 - read watchpoint,
4 - access watchpoint; ADDR is address; LENGTH is in
bytes.  For a software breakpoint, LENGTH specifies the size of
the instruction to be patched.  For hardware breakpoints and watchpoints
LENGTH specifies the memory region to be monitored.

reply ENN
for an error

reply OK
for success

If not supported.

reserved
<other>
Reserved for future use

In the case of the C, c, S and s packets, there is no immediate response.  The reply, described below, comes when the machine stops:

SAA
AA is the signal number

TAAN...:R...;N...:R...;N...:R...;

AA = two hex digit signal number; N... = register number
(hex), R...  = target byte ordered register contents, size defined
by REGISTER_RAW_SIZE; N... = thread, R... =
thread process ID, this is a hex integer; N... = other string not
starting with valid hex digit. GDBN should ignore this
N..., R... pair and go on to the next.  This way we can
extend the protocol.

WAA

The process exited, and AA is the exit status.  This is only
applicable for certains sorts of targets.

XAA

The process terminated with signal AA.

NAA;TTTTTTTT;DDDDDDDD;BBBBBBBB (obsolete)

AA = signal number; TTTTTTTT = address of symbol "_start";
DDDDDDDD = base of data section; BBBBBBBB = base of bss
section. Note: only used by Cisco Systems targets.  The difference
between this reply and the "qOffsets" query is that the 'N' packet may
arrive spontaneously whereas the 'qOffsets' is a query initiated by the
host debugger.

OXX...

XX... is hex encoding of ASCII data. This can happen at any time
while the program is running and the debugger should continue to wait
for 'W', 'T', etc.

Example sequence of a target being re-started.  Notice how the restart does not get any direct output:

     <- R00
     -> +
     target restarts
     <- ?
     -> +
     -> T001:1234123412341234
     <- +

Example sequence of a target being stepped by a single instruction:

     <- G1445...
     -> +
     <- s
     -> +
     time passes
     -> T001:1234123412341234
     <- +
     <- g
     -> +
     -> 1455...
     <- +

If you have trouble with the serial connection, you can use the command set remotedebug.  This makes GDBN report on all packets sent back and forth across the serial line to the remote machine.  The packet-debugging information is printed on the GDBN standard output stream.  set remotedebug off turns it off, and show remotedebug shows you its current state.

Using the gdbserver program
...........................

gdbserver is a control program for Unix-like systems, which allows you to connect your program with a remote GDBN via target remote---but without linking in the usual debugging stub.

gdbserver is not a complete replacement for the debugging stubs, because it requires essentially the same operating-system facilities that GDBN itself does.  In fact, a system that can run gdbserver to connect to a remote GDBN could also run GDBN locally!  gdbserver is sometimes useful nevertheless, because it is a much smaller program than GDBN itself.  It is also easier to port than all of GDBN, so you may be able to get started more quickly on a new system by using gdbserver. Finally, if you develop code for real-time systems, you may find that the tradeoffs involved in real-time operation make it more convenient to do as much development work as possible on another system, for example by cross-compiling.  You can use gdbserver to make a similar choice for debugging.

GDBN and gdbserver communicate via either a serial line or a TCP connection, using the standard GDBN remote serial protocol.

On the target machine,
     you need to have a copy of the program you want to debug. gdbserver does not need your program's symbol table, so you can strip the program if necessary to save space.  GDBN on the host system does all the symbol handling.

     To use the server, you must tell it how to communicate with GDBN; the name of your program; and the arguments for your program.  The syntax is:

          target> gdbserver COMM PROGRAM [ ARGS ... ]

     COMM is either a device name (to use a serial line) or a TCP hostname and portnumber.  For example, to debug Emacs with the argument foo.txt and communicate with GDBN over the serial port /dev/com1:

          target> gdbserver /dev/com1 emacs foo.txt

     gdbserver waits passively for the host GDBN to communicate with it.

     To use a TCP connection instead of a serial line:

          target> gdbserver host:2345 emacs foo.txt

     The only difference from the previous example is the first argument, specifying that you are communicating with the host GDBN via TCP.  The host:2345 argument means that gdbserver is to expect a TCP connection from machine host to local TCP port 2345. (Currently, the host part is ignored.)  You can choose any number you want for the port number as long as it does not conflict with any TCP ports already in use on the target system (for example, 23 is reserved for telnet). (If you choose a port number that
     conflicts with another service, gdbserver prints an error message
     and exits.) You must use the same port number with the host GDBN target remote command.

On the GDBN host machine,
     you need an unstripped copy of your program, since GDBN needs symbols and debugging information.  Start up GDBN as usual, using the name of the local copy of your program as the first argument. (You may also need the --baud option if the serial line is running at anything other than 9600 bps.)  After that, use target remote to establish communications with gdbserver.  Its argument is either a device name (usually a serial device, like /dev/ttyb), or a TCP port descriptor in the form HOST:PORT.  For example:

          (GDBP) target remote /dev/ttyb

     communicates with the server via serial line /dev/ttyb, and

          (GDBP) target remote the-target:2345

     communicates via a TCP connection to port 2345 on host the-target. For TCP connections, you must start up gdbserver prior to using the target remote command.  Otherwise you may get an error whose text depends on the host system, but which usually looks something like Connection refused.

Using the gdbserve.nlm program
..............................

gdbserve.nlm is a control program for NetWare systems, which allows you to connect your program with a remote GDBN via target remote.

GDBN and gdbserve.nlm communicate via a serial line, using the standard GDBN remote serial protocol.

On the target machine,
     you need to have a copy of the program you want to debug. gdbserve.nlm does not need your program's symbol table, so you can strip the program if necessary to save space.  GDBN on the host system does all the symbol handling.

     To use the server, you must tell it how to communicate with GDBN; the name of your program; and the arguments for your program.  The syntax is:

          load gdbserve [ BOARD=BOARD ] [ PORT=PORT ]
                        [ BAUD=BAUD ] PROGRAM [ ARGS ... ]

     BOARD and PORT specify the serial line; BAUD specifies the baud rate used by the connection.  PORT and NODE default to 0, BAUD defaults to 9600 bps.

     For example, to debug Emacs with the argument foo.txtand communicate with GDBN over serial port number 2 or board 1 using a 19200 bps connection:

          load gdbserve BOARD=1 PORT=2 BAUD=19200 emacs foo.txt

On the GDBN host machine,
     you need an unstripped copy of your program, since GDBN needs symbols and debugging information.  Start up GDBN as usual, using the name of the local copy of your program as the first argument. (You may also need the --baud option if the serial line is running at anything other than 9600 bps.  After that, use target remote to establish communications with gdbserve.nlm.  Its argument is a device name (usually a serial device, like /dev/ttyb).  For example:

          (GDBP) target remote /dev/ttyb

     communications with the server via serial line /dev/ttyb.

GDBN with a remote i960 (Nindy)
-------------------------------

Nindy is a ROM Monitor program for Intel 960 target systems.  When GDBN is configured to control a remote Intel 960 using Nindy, you can tell GDBN how to connect to the 960 in several ways:

  * Through command line options specifying serial port, version of the Nindy protocol, and communications speed;

  * By responding to a prompt on startup;

  * By using the target command at any point during your GDBN session.  See Commands for managing targets.

Startup with Nindy
..................

If you simply start GDBP without using any command-line options, you are prompted for what serial port to use, before you reach the ordinary GDBN prompt:

     Attach /dev/ttyNN -- specify NN, or "quit" to quit:

Respond to the prompt with whatever suffix (after /dev/tty) identifies the serial port you want to use.  You can, if you choose, simply start up with no Nindy connection by responding to the prompt with an empty line.  If you do this and later wish to attach to Nindy, use target (see Commands for managing targets).

Options for Nindy
.................

These are the startup options for beginning your GDBN session with a Nindy-960 board attached:

-r PORT
     Specify the serial port name of a serial interface to be used to connect to the target system.  This option is only available when GDBN is configured for the Intel 960 target architecture.  You may specify PORT as any of: a full pathname (e.g. -r /dev/ttya), a device name in /dev (e.g. -r ttya), or simply the unique suffix for a specific tty (e.g. -r a).

-O
     (An uppercase letter ``O'', not a zero.)  Specify that GDBN should use the ``old'' Nindy monitor protocol to connect to the target system. This option is only available when GDBN is configured for the Intel 960 target architecture.

          Warning: if you specify -O, but are actually trying to connect to a target system that expects the newer protocol, the connection fails, appearing to be a speed mismatch.  GDBN repeatedly attempts to reconnect at several different line speeds.  You can abort this process with an interrupt.

-brk
     Specify that GDBN should first send a BREAK signal to the target system, in an attempt to reset it, before connecting to a Nindy target.

          Warning: Many target systems do not have the hardware that this requires; it only works with a few boards.

The standard -b option controls the line speed used on the serial port.

Nindy reset command
...................

reset
     For a Nindy target, this command sends a ``break'' to the remote target system; this is only useful if the target has been equipped with a circuit to perform a hard reset (or some other interesting action) when a break is detected.

The UDI protocol for AMD29K
---------------------------

GDBN supports AMD's UDI (``Universal Debugger Interface'') protocol for debugging the a29k processor family.  To use this configuration with AMD targets running the MiniMON monitor, you need the program MONTIP, available from AMD at no charge.  You can also use GDBN with the UDI-conformant a29k simulator program ISSTIP, also available from AMD.

target udi KEYWORD
     Select the UDI interface to a remote a29k board or simulator, where KEYWORD is an entry in the AMD configuration file udi_soc. This file contains keyword entries which specify parameters used to connect to a29k targets.  If the udi_soc file is not in your working directory, you must set the environment variable UDICONF to its pathname.

The EBMON protocol for AMD29K
-----------------------------

AMD distributes a 29K development board meant to fit in a PC, together with a DOS-hosted monitor program called EBMON.  As a shorthand term, this development system is called the ``EB29K''.  To use GDBN from a Unix system to run programs on the EB29K board, you must first connect a serial cable between the PC (which hosts the EB29K board) and a serial port on the Unix system.  In the following, we assume you've hooked the cable between the PC's COM1 port and /dev/ttya on the Unix system.

Communications setup
....................

The next step is to set up the PC's port, by doing something like this in DOS on the PC:

     C:\> MODE com1:9600,n,8,1,none

This example---run on an MS DOS 4.0 system---sets the PC port to 9600 bps, no parity, eight data bits, one stop bit, and no ``retry'' action; you must match the communications parameters when establishing the Unix end of the connection as well.

To give control of the PC to the Unix side of the serial line, type the following at the DOS console:

     C:\> CTTY com1

(Later, if you wish to return control to the DOS console, you can use the command CTTY con---but you must send it over the device that had control, in our example over the COM1 serial line).

From the Unix host, use a communications program such as tip or cu to communicate with the PC; for example,

     cu -s 9600 -l /dev/ttya

The cu options shown specify, respectively, the linespeed and the serial port to use.  If you use tip instead, your command line may look something like the following:

     tip -9600 /dev/ttya

Your system may require a different name where we show /dev/ttya as the argument to tip.  The communications parameters, including which port to use, are associated with the tip argument in the ``remote'' descriptions file---normally the system table /etc/remote.

Using the tip or cu connection, change the DOS working directory to the directory containing a copy of your 29K program, then start the PC program EBMON (an EB29K control program supplied with your board by AMD).  You should see an initial display from EBMON similar to the one that follows, ending with the EBMON prompt #---

     C:\> G:

     G:\> CD \usr\joe\work29k

     G:\USR\JOE\WORK29K> EBMON
     Am29000 PC Coprocessor Board Monitor, version 3.0-18
     Copyright 1990 Advanced Micro Devices, Inc.
     Written by Gibbons and Associates, Inc.

     Enter '?' or 'H' for help

     PC Coprocessor Type   = EB29K
     I/O Base              = 0x208
     Memory Base           = 0xd0000

     Data Memory Size      = 2048KB
     Available I-RAM Range = 0x8000 to 0x1fffff
     Available D-RAM Range = 0x80002000 to 0x801fffff

     PageSize              = 0x400
     Register Stack Size   = 0x800
     Memory Stack Size     = 0x1800

     CPU PRL               = 0x3
     Am29027 Available     = No
     Byte Write Available  = Yes

     # ~.

Then exit the cu or tip program (done in the example by typing ~. at the EBMON prompt).  EBMON keeps running, ready for GDBN to take over.

For this example, we've assumed what is probably the most convenient way to make sure the same 29K program is on both the PC and the Unix system: a PC/NFS connection that establishes ``drive G:'' on the PC as a file system on the Unix host.  If you do not have PC/NFS or something similar connecting the two systems, you must arrange some other way---perhaps floppy-disk transfer---of getting the 29K program from the Unix system to the PC; GDBN does not download it over the serial line.

EB29K cross-debugging
.....................

Finally, cd to the directory containing an image of your 29K program on the Unix system, and start GDBN---specifying as argument the name of your 29K program:

     cd /usr/joe/work29k
     GDBP myfoo

Now you can use the target command:

     target amd-eb /dev/ttya 9600 MYFOO

In this example, we've assumed your program is in a file called myfoo.  Note that the filename given as the last argument to target amd-eb should be the name of the program as it appears to DOS. In our example this is simply MYFOO, but in general it can include a DOS path, and depending on your transfer mechanism may not resemble the name on the Unix side.

At this point, you can set any breakpoints you wish; when you are ready to see your program run on the 29K board, use the GDBN command run.

To stop debugging the remote program, use the GDBN detach command.

To return control of the PC to its console, use tip or cu once again, after your GDBN session has concluded, to attach to EBMON.  You can then type the command q to shut down EBMON, returning control to the DOS command-line interpreter. Type CTTY con to return command input to the main DOS console, and type ~. to leave tip or cu.

Remote log
..........

The target amd-eb command creates a file eb.log in the current working directory, to help debug problems with the connection. eb.log records all the output from EBMON, including echoes of the commands sent to it.  Running tail -f on this file in another window often helps to understand trouble with EBMON, or unexpected events on the PC side of the connection.

GDBN with a Tandem ST2000
-------------------------

To connect your ST2000 to the host system, see the manufacturer's manual.  Once the ST2000 is physically attached, you can run:

     target st2000 DEV SPEED

to establish it as your debugging environment.  DEV is normally the name of a serial device, such as /dev/ttya, connected to the ST2000 via a serial line.  You can instead specify DEV as a TCP connection (for example, to a serial line attached via a terminal concentrator) using the syntax HOSTNAME:PORTNUMBER.

The load and attach commands are not defined for this target; you must load your program into the ST2000 as you normally would for standalone operation.  GDBN reads debugging information (such as symbols) from a separate, debugging version of the program available on your host computer.

These auxiliary GDBN commands are available to help you with the ST2000 environment:

st2000 COMMAND
     Send a COMMAND to the STDBUG monitor.  See the manufacturer's manual for available commands.

connect
     Connect the controlling terminal to the STDBUG command monitor.  When you are done interacting with STDBUG, typing either of two character sequences gets you back to the GDBN command prompt: RET~. (Return, followed by tilde and period) or RET~C-d (Return, followed by tilde and control-D).

GDBN and VxWorks
----------------

GDBN enables developers to spawn and debug tasks running on networked VxWorks targets from a Unix host.  Already-running tasks spawned from the VxWorks shell can also be debugged.  GDBN uses code that runs on both the Unix host and on the VxWorks target.  The program gdb is installed and executed on the Unix host.  (It may be installed with the name vxgdb, to distinguish it from a GDBN for debugging programs on the host itself.)

VxWorks-timeout ARGS
     All VxWorks-based targets now support the option vxworks-timeout. This option is set by the user, and  ARGS represents the number of seconds GDBN waits for responses to rpc's.  You might use this if your VxWorks target is a slow software simulator or is on the far side of a thin network line.

The following information on connecting to VxWorks was current when this manual was produced; newer releases of VxWorks may use revised procedures.

To use GDBN with VxWorks, you must rebuild your VxWorks kernel to include the remote debugging interface routines in the VxWorks library rdb.a.  To do this, define INCLUDE_RDB in the VxWorks configuration file configAll.h and rebuild your VxWorks kernel.  The resulting kernel contains rdb.a, and spawns the source debugging task tRdbTask when VxWorks is booted.  For more information on configuring and remaking VxWorks, see the manufacturer's manual.

Once you have included rdb.a in your VxWorks system image and set your Unix execution search path to find GDBN, you are ready to run GDBN.  From your Unix host, run gdb (or vxgdb, depending on your installation).

GDBN comes up showing the prompt:

     (vxgdb)

Connecting to VxWorks
.....................

The GDBN command target lets you connect to a VxWorks target on the network.  To connect to a target whose host name is ``tt'', type:

     (vxgdb) target vxworks tt

GDBN displays messages like these:

     Attaching remote machine across net...
     Connected to tt.

GDBN then attempts to read the symbol tables of any object modules loaded into the VxWorks target since it was last booted.  GDBN locates these files by searching the directories listed in the command search path (see Your program's environment); if it fails to find an object file, it displays a message such as:

     prog.o: No such file or directory.

When this happens, add the appropriate directory to the search path with the GDBN command path, and execute the target command again.

VxWorks download
................

If you have connected to the VxWorks target and you want to debug an object that has not yet been loaded, you can use the GDBN load command to download a file from Unix to VxWorks incrementally.  The object file given as an argument to the load command is actually opened twice: first by the VxWorks target in order to download the code, then by GDBN in order to read the symbol table.  This can lead to problems if the current working directories on the two systems differ.  If both systems have NFS mounted the same filesystems, you can avoid these problems by using absolute paths. Otherwise, it is simplest to set the working directory on both systems to the directory in which the object file resides, and then to reference the file by its name, without any path.  For instance, a program prog.o may reside in VXPATH/vw/demo/rdb in VxWorks and in HOSTPATH/vw/demo/rdb on the host.  To load this program, type this on VxWorks:

     -> cd "VXPATH/vw/demo/rdb"

v Then, in GDBN, type:

     (vxgdb) cd HOSTPATH/vw/demo/rdb
     (vxgdb) load prog.o

GDBN displays a response similar to this:

     Reading symbol data from wherever/vw/demo/rdb/prog.o... done.

You can also use the load command to reload an object module after editing and recompiling the corresponding source file.  Note that this makes GDBN delete all currently-defined breakpoints, auto-displays, and convenience variables, and to clear the value history.  (This is necessary in order to preserve the integrity of debugger data structures that reference the target system's symbol table.)

Running tasks
.............

You can also attach to an existing task using the attach command as follows:

     (vxgdb) attach TASK

where TASK is the VxWorks hexadecimal task ID.  The task can be running or suspended when you attach to it.  Running tasks are suspended at the time of attachment.

GDBN and Sparclet
-----------------

GDBN enables developers to debug tasks running on Sparclet targets from a Unix host. GDBN uses code that runs on both the Unix host and on the Sparclet target.  The program gdb is installed and executed on the Unix host.

timeout ARGS
     GDBN now supports the option remotetimeout. This option is set by the user, and  ARGS represents the number of seconds GDBN waits for responses.

When compiling for debugging, include the options "-g" to get debug information and "-Ttext" to relocate the program to where you wish to load it on the target.  You may also want to add the options "-n" or "-N" in order to reduce the size of the sections.

     sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N

You can use objdump to verify that the addresses are what you intended.

     sparclet-aout-objdump --headers --syms prog

Once you have set your Unix execution search path to find GDBN, you are ready to run GDBN.  From your Unix host, run gdb (or sparclet-aout-gdb, depending on your installation).

GDBN comes up showing the prompt:

     (gdbslet)

Setting file to debug
.....................

The GDBN command file lets you choose with program to debug.

     (gdbslet) file prog

GDBN then attempts to read the symbol table of prog. GDBN locates the file by searching the directories listed in the command search path. If the file was compiled with debug information (option "-g"), source files will be searched as well. GDBN locates the source files by searching the directories listed in the directory search path (see Your program's environment). If it fails to find a file, it displays a message such as:

     prog: No such file or directory.

When this happens, add the appropriate directories to the search paths with the GDBN commands path and dir, and execute the target command again.

Connecting to Sparclet
......................

The GDBN command target lets you connect to a Sparclet target. To connect to a target on serial port ``ttya'', type:

     (gdbslet) target sparclet /dev/ttya
     Remote target sparclet connected to /dev/ttya
     main () at ../prog.c:3

GDBN displays messages like these:

     Connected to ttya.

Sparclet download
.................

Once connected to the Sparclet target, you can use the GDBN load command to download the file from the host to the target. The file name and load offset should be given as arguments to the load command. Since the file format is aout, the program must be loaded to the starting address.  You can use objdump to find out what this value is.  The load offset is an offset which is added to the VMA (virtual memory address) of each of the file's sections. For instance, if the program prog was linked to text address 0x1201000, with data at 0x12010160 and bss at 0x12010170, in GDBN, type:

     (gdbslet) load prog 0x12010000
     Loading section .text, size 0xdb0 vma 0x12010000

If the code is loaded at a different address then what the program was linked to, you may need to use the section and add-symbol-file commands to tell GDBN where to map the symbol table.

Running and debugging
.....................

You can now begin debugging the task using GDBN's execution control commands, b, step, run, etc.  See the GDBN manual for the list of commands.

     (gdbslet) b main
     Breakpoint 1 at 0x12010000: file prog.c, line 3.
     (gdbslet) run
     Starting program: prog
     Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
     3        char *symarg = 0;
     (gdbslet) step
     4        char *execarg = "hello!";
     (gdbslet)

GDBN and Hitachi microprocessors
--------------------------------

GDBN needs to know these things to talk to your Hitachi SH, H8/300, or H8/500:

 1. that you want to use target hms, the remote debugging interface for Hitachi microprocessors, or target e7000, the in-circuit emulator for the Hitachi SH and the Hitachi 300H.  (target hms is the default when GDB is configured specifically for the Hitachi SH, H8/300, or H8/500.)

 2. what serial device connects your host to your Hitachi board (the first serial device available on your host is the default).

 3. what speed to use over the serial device.

Connecting to Hitachi boards
............................

Use the special GDBP command device PORT if you need to explicitly set the serial device.  The default PORT is the first available port on your host.  This is only necessary on Unix hosts, where it is typically something like /dev/ttya.

GDBP has another special command to set the communications speed: speed BPS.  This command also is only used from Unix hosts; on DOS hosts, set the line speed as usual from outside GDB with the DOS mode command (for instance, mode com2:9600,n,8,1,p for a 9600 bps connection).

The device and speed commands are available only when you use a Unix host to debug your Hitachi microprocessor programs.  If you use a DOS host, GDBN depends on an auxiliary terminate-and-stay-resident program called asynctsr to communicate with the development board through a PC serial port.  You must also use the DOS mode command to set up the serial port on the DOS side.

The following sample session illustrates the steps needed to start a program under GDBN control on an H8/300.  The example uses a sample H8/300 program called t.x.  The procedure is the same for the Hitachi SH and the H8/500.

First hook up your development board.  In this example, we use a board attached to serial port COM2; if you use a different serial port, substitute its name in the argument of the mode command. When you call asynctsr, the auxiliary comms program used by the degugger, you give it just the numeric part of the serial port's name; for example, asyncstr 2 below runs asyncstr on COM2.

     C:\H8300\TEST> asynctsr 2
     C:\H8300\TEST> mode com2:9600,n,8,1,p

     Resident portion of MODE loaded

     COM2: 9600, n, 8, 1, p

     Warning: We have noticed a bug in PC-NFS that conflicts with asynctsr.  If you also run PC-NFS on your DOS host, you may need to disable it, or even boot without it, to use asynctsr to control your development board.

Now that serial communications are set up, and the development board is connected, you can start up GDBN.  Call GDBP with the name of your program as the argument.  GDBP prompts you, as usual, with the prompt (GDBP).  Use two special commands to begin your debugging session: target hms to specify cross-debugging to the Hitachi board, and the load command to download your program to the board.  load displays the names of the program's sections, and a * for each 2K of data downloaded. (If you want to refresh GDBN data on symbols or on the executable file without downloading, use the GDBN commands file or symbol-file.  These commands, and load itself, are described in Commands to specify files.)

     (eg-C:\H8300\TEST) GDBP t.x
     GDB is free software and you are welcome to distribute copies
      of it under certain conditions; type "show copying" to see
      the conditions.
     There is absolutely no warranty for GDB; type "show warranty"
     for details.
     GDB GDBVN, Copyright 1992 Free Software Foundation, Inc...
     (gdb) target hms
     Connected to remote H8/300 HMS system.
     (gdb) load t.x
     .text   : 0x8000 .. 0xabde ***********
     .data   : 0xabde .. 0xad30 *
     .stack  : 0xf000 .. 0xf014 *

At this point, you're ready to run or debug your program.  From here on, you can use all the usual GDBN commands.  The break command sets breakpoints; the run command starts your program; print or x display data; the continue command resumes execution after stopping at a breakpoint.  You can use the help command at any time to find out more about GDBN commands.

Remember, however, that operating system facilities aren't available on your development board; for example, if your program hangs, you can't send an interrupt---but you can press the RESET switch!

Use the RESET button on the development board

  * to interrupt your program (don't use ctl-C on the DOS host---it has no way to pass an interrupt signal to the development board); and

  * to return to the GDBN command prompt after your program finishes normally.  The communications protocol provides no other way for GDBN to detect program completion.

In either case, GDBN sees the effect of a RESET on the development board as a ``normal exit'' of your program.

Using the E7000 in-circuit emulator
...................................

You can use the E7000 in-circuit emulator to develop code for either the Hitachi SH or the H8/300H.  Use one of these forms of the target
e7000 command to connect GDBN to your E7000:

target e7000 PORT SPEED
     Use this form if your E7000 is connected to a serial port.  The PORT argument identifies what serial port to use (for example, com2).  The third argument is the line speed in bits per second (for example, 9600).

target e7000 HOSTNAME
     If your E7000 is installed as a host on a TCP/IP network, you can just specify its hostname; GDBN uses telnet to connect.

Special GDBN commands for Hitachi micros
........................................

Some GDBN commands are available only on the H8/300 or the H8/500 configurations:

set machine h8300
set machine h8300h
     Condition GDBN for one of the two variants of the H8/300 architecture with set machine.  You can use show machine to check which variant is currently in effect.

set memory MOD
show memory
     Specify which H8/500 memory model (MOD) you are using with set memory; check which memory model is in effect with show memory.  The accepted values for MOD are small, big, medium, and compact.

GDBN and remote MIPS boards
---------------------------

GDBN can use the MIPS remote debugging protocol to talk to a MIPS board attached to a serial line.  This is available when you configure GDBN with --target=mips-idt-ecoff.

Use these GDBN commands to specify the connection to your target board:

target mips PORT
     To run a program on the board, start up GDBP with the name of your program as the argument.  To connect to the board, use the command target mips PORT, where PORT is the name of the serial port connected to the board.  If the program has not already been downloaded to the board, you may use the load command to download it.  You can then use all the usual GDBN commands.

     For example, this sequence connects to the target board through a serial port, and loads and runs a program called PROG through the debugger:

          host$ GDBP PROG
          GDB is free software and ...
          (gdb) target mips /dev/ttyb
          (gdb) load PROG
          (gdb) run

target mips HOSTNAME:PORTNUMBER
     On some GDBN host configurations, you can specify a TCP connection (for instance, to a serial line managed by a terminal concentrator) instead of a serial port, using the syntax HOSTNAME:PORTNUMBER.

target pmon PORT

target ddb PORT

target lsi PORT

GDBN also supports these special commands for MIPS targets:

set processor ARGS
show processor
     Use the set processor command to set the type of MIPS processor when you want to access processor-type-specific registers. For example, set processor R3041 tells GDBN to use the CPO registers appropriate for the 3041 chip. Use the show processor command to see what MIPS processor GDBN is using.  Use the info reg command to see what registers GDBN is using.

set mipsfpu double
set mipsfpu single
set mipsfpu none
show mipsfpu
     If your target board does not support the MIPS floating point coprocessor, you should use the command set mipsfpu none (if you need this, you may wish to put the command in your GDBINIT file).  This tells GDBN how to find the return value of functions which return floating point values.  It also allows GDBN to avoid saving the floating point registers when calling functions on the board.  If you are using a floating point coprocessor with only single precision floating point support, as on the R4650 processor, use the command set mipsfpu single.  The default double precision floating point coprocessor may be selected using set mipsfpu double.

     In previous versions the only choices were double precision or no floating point, so set mipsfpu on will select double precision and set mipsfpu off will select no floating point.

     As usual, you can inquire about the mipsfpu variable with show mipsfpu.

set remotedebug N
show remotedebug
     You can see some debugging information about communications with the board by setting the remotedebug variable.  If you set it to 1 using set remotedebug 1, every packet is displayed.  If you set it to 2, every character is displayed.  You can check the current value at any time with the command show remotedebug.

set timeout SECONDS
set retransmit-timeout SECONDS
show timeout
show retransmit-timeout
     You can control the timeout used while waiting for a packet, in the MIPS remote protocol, with the set timeout SECONDS command.  The default is 5 seconds.  Similarly, you can control the timeout used while waiting for an acknowledgement of a packet with the set retransmit-timeout SECONDS command.  The default is 3 seconds. You can inspect both values with show timeout and show retransmit-timeout.  (These commands are only available when GDBN is configured for --target=mips-idt-ecoff.)

     The timeout set by set timeout does not apply when GDBN is waiting for your program to stop.  In that case, GDBN waits forever because it has no way of knowing how long the program is going to run before stopping.

Simulated CPU target
--------------------

For some configurations, GDBN includes a CPU simulator that you can use instead of a hardware CPU to debug your programs. Currently, simulators are available for ARM, D10V, D30V, FR30, H8/300, H8/500, i960, M32R, MIPS, MN10200, MN10300, PowerPC, SH, Sparc, V850, W65, and Z8000.

When configured for debugging Zilog Z8000 targets, GDBN includes a Z8000 simulator.

For the Z8000 family, target sim simulates either the Z8002 (the unsegmented variant of the Z8000 architecture) or the Z8001 (the segmented variant).  The simulator recognizes which architecture is appropriate by inspecting the object code.

target sim ARGS
     Debug programs on a simulated CPU.  If the simulator supports setup options, specify them via ARGS.

After specifying this target, you can debug programs for the simulated CPU in the same style as programs for your host computer; use the file command to load a new program image, the run command to run your program, and so on.

As well as making available all the usual machine registers (see info reg), the Z8000 simulator provides three additional items of information as specially named registers:

cycles
     Counts clock-ticks in the simulator.

insts
     Counts instructions run in the simulator.

time
     Execution time in 60ths of a second.

You can refer to these values in GDBN expressions with the usual conventions; for example, b fputc if $cycles>5000 sets a conditional breakpoint that suspends only after at least 5000 simulated clock ticks.