* remote.texi (Bootstrapping): Clarify that flush_i_cache is only

[deliverable/binutils-gdb.git] / gdb / doc / remote.texi

@c								-*- Texinfo -*-
@c Copyright (c) 1990 1991 1992 1993 Free Software Foundation, Inc.
@c This file is part of the source for the GDB manual.
@c This text diverted to "Remote Debugging" section in general case;
@c however, if we're doing a manual specifically for one of these, it
@c belongs up front (in "Getting In and Out" chapter).

@ifset REMOTESTUB
@node Remote Serial
@subsection The @value{GDBN} remote serial protocol

@cindex remote serial debugging, overview
To debug a program running on another machine (the debugging
@dfn{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

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

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

@item
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.
@end enumerate

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

@table @emph
@item On the host,
@value{GDBN} already understands how to use this protocol; when everything
else is set up, you can simply use the @samp{target remote} command
(@pxref{Targets,,Specifying a Debugging Target}).

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

@ifset GDBSERVER
On certain remote targets, you can use an auxiliary program
@code{gdbserver} instead of linking a stub into your program.
@xref{Server,,Using the @code{gdbserver} program}, for details.
@end ifset
@end table

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

@cindex remote serial stub list
These working remote stubs are distributed with @value{GDBN}:

@table @code
@item sparc-stub.c
@kindex sparc-stub.c
For @sc{sparc} architectures.

@item m68k-stub.c
@kindex m68k-stub.c
@cindex Motorola 680x0
@cindex m680x0
For Motorola 680x0 architectures.

@item i386-stub.c
@kindex i386-stub.c
@cindex Intel
@cindex i386
For Intel 386 and compatible architectures.
@end table

The @file{README} file in the @value{GDBN} distribution may list other
recently added stubs.

@menu
* Stub Contents::       What the stub can do for you
* Bootstrapping::       What you must do for the stub
* Debug Session::       Putting it all together
* Protocol::            Outline of the communication protocol
@ifset GDBSERVER
* Server::		Using the `gdbserver' program
@end ifset
@ifset GDBSERVE
* NetWare::		Using the `gdbserve.nlm' program
@end ifset
@end menu

@node Stub Contents
@subsubsection What the stub can do for you

@cindex remote serial stub
The debugging stub for your architecture supplies these three
subroutines:

@table @code
@item set_debug_traps
@kindex set_debug_traps
@cindex remote serial stub, initialization
This routine arranges for @code{handle_exception} to run when your
program stops.  You must call this subroutine explicitly near the
beginning of your program.

@item handle_exception
@kindex handle_exception
@cindex remote serial stub, main routine
This is the central workhorse, but your program never calls it
explicitly---the setup code arranges for @code{handle_exception} to
run when a trap is triggered.

@code{handle_exception} takes control when your program stops during
execution (for example, on a breakpoint), and mediates communications
with @value{GDBN} on the host machine.  This is where the communications
protocol is implemented; @code{handle_exception} acts as the @value{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 @value{GDBN} needs, until you
execute a @value{GDBN} command that makes your program resume; at that point,
@code{handle_exception} returns control to your own code on the target
machine. 

@item breakpoint
@cindex @code{breakpoint} subroutine, remote
Use this auxiliary subroutine to make your program contain a
breakpoint.  Depending on the particular situation, this may be the only
way for @value{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
@code{handle_exception}---in effect, to @value{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 @code{breakpoint} from
your own program---simply running @samp{target remote} from the host
@value{GDBN} session gets control.  

Call @code{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.
@end table

@node Bootstrapping
@subsubsection What you must do for the stub

@cindex remote stub, support routines
The debugging stubs that come with @value{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.

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

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

@cindex control C, and remote debugging
@cindex interrupting remote targets
If you want @value{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 @code{^C} (@samp{\003}, the control-C
character).  That is the character which @value{GDBN} uses to tell the
remote system to stop.

Getting the debugging target to return the proper status to @value{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
@value{GDBN} reports a @code{SIGTRAP} instead of a @code{SIGINT}).

Other routines you need to supply are:

@table @code
@item void exceptionHandler (int @var{exception_number}, void *@var{exception_address})
@kindex exceptionHandler
Write this function to install @var{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 @sc{rom},
containing entries which point to a table in @sc{ram}).
@var{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
@var{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 @var{exception_address}, it
should be a simple jump, not a jump to subroutine.

For the 386, @var{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
@sc{sparc} and 68k stubs are able to mask interrupts themself without
help from @code{exceptionHandler}.

@item void flush_i_cache()
@kindex 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, @value{GDBN} requires this
function to make certain that the state of your program is stable.
@end table

@noindent
You must also make sure this library routine is available:

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

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 @code{gcc} generates as inline code.


@node Debug Session
@subsubsection Putting it all together

@cindex remote serial debugging summary
In summary, when your program is ready to debug, you must follow these
steps.

@enumerate
@item
Make sure you have the supporting low-level routines
(@pxref{Bootstrapping,,What you must do for the stub}):
@display
@code{getDebugChar}, @code{putDebugChar},
@code{flush_i_cache}, @code{memset}, @code{exceptionHandler}.
@end display

@item
Insert these lines near the top of your program:

@example
set_debug_traps();
breakpoint();
@end example

@item
For the 680x0 stub only, you need to provide a variable called
@code{exceptionHook}.  Normally you just use

@example
void (*exceptionHook)() = 0;
@end example

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

@item
Compile and link together: your program, the @value{GDBN} debugging stub for
your target architecture, and the supporting subroutines.

@item
Make sure you have a serial connection between your target machine and
the @value{GDBN} host, and identify the serial port used for this on the host.

@item
@c The "remote" target now provides a `load' command, so we should
@c document that.  FIXME.
Download your program to your target machine (or get it there by
whatever means the manufacturer provides), and start it.

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

@cindex serial line, @code{target remote}
Then establish communication using the @code{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 @file{/dev/ttyb}:

@example
target remote /dev/ttyb
@end example

@cindex TCP port, @code{target remote}
To use a TCP connection, use an argument of the form
@code{@var{host}:port}.  For example, to connect to port 2828 on a
terminal server named @code{manyfarms}:

@example
target remote manyfarms:2828
@end example
@end enumerate

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 @code{detach}
command.

@cindex interrupting remote programs
@cindex remote programs, interrupting
Whenever @value{GDBN} is waiting for the remote program, if you type the
interrupt character (often @key{C-C}), @value{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, @value{GDBN} displays this prompt:

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

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

@node Protocol
@subsubsection Communication protocol

@cindex debugging stub, example
@cindex remote stub, example
@cindex stub example, remote debugging
The stub files provided with @value{GDBN} implement the target side of the
communication protocol, and the @value{GDBN} side is implemented in the
@value{GDBN} source file @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.  @file{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 @value{GDBN}.

@cindex protocol, @value{GDBN} remote serial
@cindex serial protocol, @value{GDBN} remote
@cindex remote serial protocol
All @value{GDBN} commands and responses (other than acknowledgements, which
are single characters) are sent as a packet which includes a
checksum.  A packet is introduced with the character @samp{$}, and ends
with the character @samp{#} followed by a two-digit checksum:

@example
$@var{packet info}#@var{checksum}
@end example

@cindex checksum, for @value{GDBN} remote
@noindent
@var{checksum} is computed as the modulo 256 sum of the @var{packet
info} characters.

When either the host or the target machine receives a packet, the first
response expected is an acknowledgement: a single character, either
@samp{+} (to indicate the package was received correctly) or @samp{-}
(to request retransmission).

The host (@value{GDBN}) sends commands, and the target (the debugging stub
incorporated in your program) sends data in response.  The target also
sends data when your program stops.

Command packets are distinguished by their first character, which
identifies the kind of command.

These are the commands currently supported:

@table @code
@item g
Requests the values of CPU registers.

@item G
Sets the values of CPU registers.

@item m@var{addr},@var{count}
Read @var{count} bytes at location @var{addr}.

@item M@var{addr},@var{count}:@dots{}
Write @var{count} bytes at location @var{addr}.

@need 500
@item c
@itemx c@var{addr}
Resume execution at the current address (or at @var{addr} if supplied).

@need 500
@item s
@itemx s@var{addr}
Step the target program for one instruction, from either the current
program counter or from @var{addr} if supplied.

@item k
Kill the target program.

@item ?
Report the most recent signal.  To allow you to take advantage of the
@value{GDBN} signal handling commands, one of the functions of the debugging
stub is to report CPU traps as the corresponding POSIX signal values.
@end table

@kindex set remotedebug
@kindex show remotedebug
@cindex packets, reporting on stdout
@cindex serial connections, debugging
If you have trouble with the serial connection, you can use the command
@code{set remotedebug}.  This makes @value{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 @value{GDBN} standard output
stream.  @code{set remotedebug off} turns it off, and @code{show
remotedebug} shows you its current state.

@ifset GDBSERVER
@node Server
@subsubsection Using the @code{gdbserver} program

@kindex gdbserver
@cindex remote connection without stubs
@code{gdbserver} is a control program for Unix-like systems, which
allows you to connect your program with a remote @value{GDBN} via
@code{target remote}---but without linking in the usual debugging stub.

@code{gdbserver} is not a complete replacement for the debugging stubs,
because it requires essentially the same operating-system facilities
that @value{GDBN} itself does.  In fact, a system that can run
@code{gdbserver} to connect to a remote @value{GDBN} could also run
@value{GDBN} locally!  @code{gdbserver} is sometimes useful nevertheless,
because it is a much smaller program than @value{GDBN} itself.  It is
also easier to port than all of @value{GDBN}, so you may be able to get
started more quickly on a new system by using @code{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 @code{gdbserver} to make a similar
choice for debugging.

@value{GDBN} and @code{gdbserver} communicate via either a serial line
or a TCP connection, using the standard @value{GDBN} remote serial
protocol.

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

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

@smallexample
target> gdbserver @var{comm} @var{program} [ @var{args} @dots{} ]
@end smallexample

@var{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
@samp{foo.txt} and communicate with @value{GDBN} over the serial port
@file{/dev/com1}:

@smallexample
target> gdbserver /dev/com1 emacs foo.txt
@end smallexample

@code{gdbserver} waits passively for the host @value{GDBN} to communicate
with it.

To use a TCP connection instead of a serial line:

@smallexample
target> gdbserver host:2345 emacs foo.txt
@end smallexample

The only difference from the previous example is the first argument,
specifying that you are communicating with the host @value{GDBN} via
TCP.  The @samp{host:2345} argument means that @code{gdbserver} is to
expect a TCP connection from machine @samp{host} to local TCP port 2345.
(Currently, the @samp{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, @code{23} is
reserved for @code{telnet}).@footnote{If you choose a port number that
conflicts with another service, @code{gdbserver} prints an error message
and exits.} You must use the same port number with the host @value{GDBN}
@code{target remote} command.

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

@smallexample
(@value{GDBP}) target remote /dev/ttyb
@end smallexample

@noindent
communicates with the server via serial line @file{/dev/ttyb}, and

@smallexample
(@value{GDBP}) target remote the-target:2345
@end smallexample

@noindent
communicates via a TCP connection to port 2345 on host @w{@file{the-target}}.
For TCP connections, you must start up @code{gdbserver} prior to using
the @code{target remote} command.  Otherwise you may get an error whose
text depends on the host system, but which usually looks something like
@samp{Connection refused}.
@end table
@end ifset

@ifset GDBSERVE
@node NetWare
@subsubsection Using the @code{gdbserve.nlm} program

@kindex gdbserve.nlm
@code{gdbserve.nlm} is a control program for NetWare systems, which
allows you to connect your program with a remote @value{GDBN} via
@code{target remote}.

@value{GDBN} and @code{gdbserve.nlm} communicate via a serial line,
using the standard @value{GDBN} remote serial protocol.

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

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

@smallexample 
load gdbserve [ BOARD=@var{board} ] [ PORT=@var{port} ] [ BAUD=@var{baud} ] @var{program} [ @var{args} @dots{} ]
@end smallexample

@var{board} and @var{port} specify the serial line; @var{baud} specifies
the baud rate used by the connection.  @var{port} and @var{node} default
to 0, @var{baud} defaults to 9600 bps.

For example, to debug Emacs with the argument @samp{foo.txt}and
communicate with @value{GDBN} over serial port number 2 or board 1 
using a 19200 bps connection:

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

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

@smallexample
(@value{GDBP}) target remote /dev/ttyb
@end smallexample

@noindent
communications with the server via serial line @file{/dev/ttyb}.
@end table
@end ifset

@end ifset

@ifset I960
@node i960-Nindy Remote
@subsection @value{GDBN} with a remote i960 (Nindy)

@cindex Nindy
@cindex i960
@dfn{Nindy} is a ROM Monitor program for Intel 960 target systems.  When
@value{GDBN} is configured to control a remote Intel 960 using Nindy, you can
tell @value{GDBN} how to connect to the 960 in several ways:

@itemize @bullet
@item
Through command line options specifying serial port, version of the
Nindy protocol, and communications speed;

@item
By responding to a prompt on startup;

@item
By using the @code{target} command at any point during your @value{GDBN}
session.  @xref{Target Commands, ,Commands for managing targets}.

@end itemize

@menu
* Nindy Startup::               Startup with Nindy
* Nindy Options::               Options for Nindy
* Nindy Reset::                 Nindy reset command
@end menu

@node Nindy Startup
@subsubsection Startup with Nindy

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

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

@noindent
Respond to the prompt with whatever suffix (after @samp{/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 @code{target} (@pxref{Target Commands, ,Commands for managing targets}).

@node Nindy Options
@subsubsection Options for Nindy

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

@table @code
@item -r @var{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 @value{GDBN} is
configured for the Intel 960 target architecture.  You may specify
@var{port} as any of: a full pathname (e.g. @samp{-r /dev/ttya}), a
device name in @file{/dev} (e.g. @samp{-r ttya}), or simply the unique
suffix for a specific @code{tty} (e.g. @samp{-r a}).

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

@quotation
@emph{Warning:} if you specify @samp{-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.  @value{GDBN} repeatedly
attempts to reconnect at several different line speeds.  You can abort
this process with an interrupt.
@end quotation

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

@quotation
@emph{Warning:} Many target systems do not have the hardware that this
requires; it only works with a few boards.
@end quotation
@end table

The standard @samp{-b} option controls the line speed used on the serial
port.

@c @group
@node Nindy Reset
@subsubsection Nindy reset command

@table @code
@item reset
@kindex 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.
@end table
@c @end group
@end ifset

@ifset AMD29K
@node UDI29K Remote
@subsection The UDI protocol for AMD29K

@cindex UDI
@cindex AMD29K via UDI
@value{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 @code{MONTIP}, available from AMD at no charge.  You can also
use @value{GDBN} with the UDI conformant a29k simulator program
@code{ISSTIP}, also available from AMD.

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

@node EB29K Remote
@subsection The EBMON protocol for AMD29K

@cindex EB29K board
@cindex running 29K programs

AMD distributes a 29K development board meant to fit in a PC, together
with a DOS-hosted monitor program called @code{EBMON}.  As a shorthand
term, this development system is called the ``EB29K''.  To use
@value{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 @file{COM1} port and
@file{/dev/ttya} on the Unix system.

@menu
* Comms (EB29K)::               Communications setup
* gdb-EB29K::                   EB29K cross-debugging
* Remote Log::                  Remote log
@end menu

@node Comms (EB29K)
@subsubsection Communications setup

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

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

@noindent
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.
@c FIXME: Who knows what this "no retry action" crud from the DOS manual may
@c       mean?  It's optional; leave it out? ---pesch@cygnus.com, 25feb91 

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

@example
C:\> CTTY com1
@end example

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

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

@example
cu -s 9600 -l /dev/ttya
@end example

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

@example
tip -9600 /dev/ttya
@end example

@noindent
Your system may require a different name where we show
@file{/dev/ttya} as the argument to @code{tip}.  The communications
parameters, including which port to use, are associated with the
@code{tip} argument in the ``remote'' descriptions file---normally the
system table @file{/etc/remote}.
@c FIXME: What if anything needs doing to match the "n,8,1,none" part of
@c the DOS side's comms setup?  cu can support -o (odd
@c parity), -e (even parity)---apparently no settings for no parity or
@c for character size.  Taken from stty maybe...?  John points out tip
@c can set these as internal variables, eg ~s parity=none; man stty
@c suggests that it *might* work to stty these options with stdin or
@c stdout redirected... ---pesch@cygnus.com, 25feb91

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

@example
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

# ~.
@end example

Then exit the @code{cu} or @code{tip} program (done in the example by
typing @code{~.} at the @code{EBMON} prompt).  @code{EBMON} keeps
running, ready for @value{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 @code{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; @value{GDBN} does @emph{not} download it over the
serial line.

@node gdb-EB29K
@subsubsection EB29K cross-debugging

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

@example
cd /usr/joe/work29k
@value{GDBP} myfoo
@end example

@need 500
Now you can use the @code{target} command:

@example
target amd-eb /dev/ttya 9600 MYFOO
@c FIXME: test above 'target amd-eb' as spelled, with caps!  caps are meant to
@c emphasize that this is the name as seen by DOS (since I think DOS is
@c single-minded about case of letters).  ---pesch@cygnus.com, 25feb91
@end example

@noindent
In this example, we've assumed your program is in a file called
@file{myfoo}.  Note that the filename given as the last argument to
@code{target amd-eb} should be the name of the program as it appears to DOS.
In our example this is simply @code{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 @value{GDBN} command
@code{run}.

To stop debugging the remote program, use the @value{GDBN} @code{detach}
command.

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

@node Remote Log
@subsubsection Remote log
@kindex eb.log
@cindex log file for EB29K

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

@end ifset

@ifset ST2000
@node ST2000 Remote
@subsection @value{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

@example
target st2000 @var{dev} @var{speed}
@end example

@noindent
to establish it as your debugging environment.  @var{dev} is normally
the name of a serial device, such as @file{/dev/ttya}, connected to the
ST2000 via a serial line.  You can instead specify @var{dev} as a TCP
connection (for example, to a serial line attached via a terminal
concentrator) using the syntax @code{@var{hostname}:@var{portnumber}}.

The @code{load} and @code{attach} commands are @emph{not} defined for
this target; you must load your program into the ST2000 as you normally
would for standalone operation.  @value{GDBN} reads debugging information
(such as symbols) from a separate, debugging version of the program
available on your host computer.
@c FIXME!! This is terribly vague; what little content is here is
@c basically hearsay.

@cindex ST2000 auxiliary commands
These auxiliary @value{GDBN} commands are available to help you with the ST2000
environment:

@table @code
@item st2000 @var{command}
@kindex st2000 @var{cmd}
@cindex STDBUG commands (ST2000)
@cindex commands to STDBUG (ST2000)
Send a @var{command} to the STDBUG monitor.  See the manufacturer's
manual for available commands.

@item connect
@cindex connect (to STDBUG)
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 @value{GDBN} command prompt:
@kbd{@key{RET}~.} (Return, followed by tilde and period) or
@kbd{@key{RET}~@key{C-d}} (Return, followed by tilde and control-D).
@end table
@end ifset

@ifset VXWORKS
@node VxWorks Remote
@subsection @value{GDBN} and VxWorks
@cindex VxWorks

@value{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.  @value{GDBN} uses code that runs on
both the Unix host and on the VxWorks target.  The program
@code{gdb} is installed and executed on the Unix host.  (It may be
installed with the name @code{vxgdb}, to distinguish it from a
@value{GDBN} for debugging programs on the host itself.)

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

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

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

@value{GDBN} comes up showing the prompt:

@example
(vxgdb)
@end example

@menu
* VxWorks Connection::          Connecting to VxWorks
* VxWorks Download::            VxWorks download
* VxWorks Attach::              Running tasks
@end menu

@node VxWorks Connection
@subsubsection Connecting to VxWorks

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

@example
(vxgdb) target vxworks tt
@end example

@need 750
@value{GDBN} displays messages like these:

@smallexample
Attaching remote machine across net... 
Connected to tt.
@end smallexample

@need 1000
@value{GDBN} then attempts to read the symbol tables of any object modules
loaded into the VxWorks target since it was last booted.  @value{GDBN} locates
these files by searching the directories listed in the command search
path (@pxref{Environment, ,Your program's environment}); if it fails
to find an object file, it displays a message such as:

@example
prog.o: No such file or directory.
@end example

When this happens, add the appropriate directory to the search path with
the @value{GDBN} command @code{path}, and execute the @code{target}
command again.

@node VxWorks Download
@subsubsection VxWorks download

@cindex download to VxWorks
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 @value{GDBN}
@code{load} command to download a file from Unix to VxWorks
incrementally.  The object file given as an argument to the @code{load}
command is actually opened twice: first by the VxWorks target in order
to download the code, then by @value{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
@file{prog.o} may reside in @file{@var{vxpath}/vw/demo/rdb} in VxWorks
and in @file{@var{hostpath}/vw/demo/rdb} on the host.  To load this
program, type this on VxWorks:

@example
-> cd "@var{vxpath}/vw/demo/rdb"
@end example

Then, in @value{GDBN}, type:

@example
(vxgdb) cd @var{hostpath}/vw/demo/rdb 
(vxgdb) load prog.o
@end example

@value{GDBN} displays a response similar to this:

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

You can also use the @code{load} command to reload an object module
after editing and recompiling the corresponding source file.  Note that
this makes @value{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.)

@node VxWorks Attach
@subsubsection Running tasks

@cindex running VxWorks tasks
You can also attach to an existing task using the @code{attach} command as
follows:

@example
(vxgdb) attach @var{task}
@end example

@noindent
where @var{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.
@end ifset

@ifset H8
@node Hitachi Remote
@subsection @value{GDBN} and Hitachi microprocessors
@value{GDBN} needs to know these things to talk to your
Hitachi SH, H8/300, or H8/500: 

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

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

@ifclear H8EXCLUSIVE
@c this is only for Unix hosts, not of interest to Hitachi
@item
what speed to use over the serial device.
@end ifclear
@end enumerate

@menu
* Hitachi Boards::      Connecting to Hitachi boards.
* Hitachi ICE::         Using the E7000 In-Circuit Emulator.
* Hitachi Special::     Special @value{GDBN} commands for Hitachi micros.
@end menu

@node Hitachi Boards
@subsubsection Connecting to Hitachi boards

@ifclear H8EXCLUSIVE
@c only for Unix hosts
@kindex device
@cindex serial device, Hitachi micros
Use the special @code{@value{GDBP}} command @samp{device @var{port}} if you
need to explicitly set the serial device.  The default @var{port} is the
first available port on your host.  This is only necessary on Unix
hosts, where it is typically something like @file{/dev/ttya}.

@kindex speed
@cindex serial line speed, Hitachi micros
@code{@value{GDBP}} has another special command to set the communications
speed: @samp{speed @var{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 @kbd{mode} command (for instance, @w{@samp{mode
com2:9600,n,8,1,p}} for a 9600 bps connection).

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

@ifset DOSHOST
The following sample session illustrates the steps needed to start a
program under @value{GDBN} control on an H8/300.  The example uses a
sample H8/300 program called @file{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 @code{COM2}; if you use a different serial
port, substitute its name in the argument of the @code{mode} command.
When you call @code{asynctsr}, the auxiliary comms program used by the
degugger, you give it just the numeric part of the serial port's name;
for example, @samp{asyncstr 2} below runs @code{asyncstr} on
@code{COM2}.

@example
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

@end example

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

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

@smallexample
(eg-C:\H8300\TEST) @value{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 @value{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 *
@end smallexample

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

Remember, however, that @emph{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 @sc{reset} switch!

Use the @sc{reset} button on the development board
@itemize @bullet
@item
to interrupt your program (don't use @kbd{ctl-C} on the DOS host---it has
no way to pass an interrupt signal to the development board); and

@item
to return to the @value{GDBN} command prompt after your program finishes
normally.  The communications protocol provides no other way for @value{GDBN}
to detect program completion.
@end itemize

In either case, @value{GDBN} sees the effect of a @sc{reset} on the
development board as a ``normal exit'' of your program.
@end ifset

@node Hitachi ICE
@subsubsection Using the E7000 in-circuit emulator

@kindex target e7000
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 @samp{target
e7000} command to connect @value{GDBN} to your E7000:

@table @code
@item target e7000 @var{port} @var{speed}
Use this form if your E7000 is connected to a serial port.  The
@var{port} argument identifies what serial port to use (for example,
@samp{com2}).  The third argument is the line speed in bits per second
(for example, @samp{9600}).

@item target e7000 @var{hostname}
If your E7000 is installed as a host on a TCP/IP network, you can just
specify its hostname; @value{GDBN} uses @code{telnet} to connect.
@end table

@node Hitachi Special
@subsubsection Special @value{GDBN} commands for Hitachi micros

Some @value{GDBN} commands are available only on the H8/300 or the
H8/500 configurations:

@table @code
@kindex set machine
@kindex show machine
@item set machine h8300
@itemx set machine h8300h
Condition @value{GDBN} for one of the two variants of the H8/300
architecture with @samp{set machine}.  You can use @samp{show machine}
to check which variant is currently in effect.

@kindex set memory @var{mod}
@cindex memory models, H8/500
@item set memory @var{mod}
@itemx show memory
Specify which H8/500 memory model (@var{mod}) you are using with
@samp{set memory}; check which memory model is in effect with @samp{show
memory}.  The accepted values for @var{mod} are @code{small},
@code{big}, @code{medium}, and @code{compact}.
@end table

@end ifset

@ifset MIPS
@node MIPS Remote
@subsection @value{GDBN} and remote MIPS boards

@cindex MIPS boards
@value{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 @value{GDBN} with @samp{--target=mips-idt-ecoff}.

@need 1000
Use these @value{GDBN} commands to specify the connection to your target board:

@table @code
@item target mips @var{port}
@kindex target mips @var{port}
To run a program on the board, start up @code{@value{GDBP}} with the
name of your program as the argument.  To connect to the board, use the
command @samp{target mips @var{port}}, where @var{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 @code{load} command to
download it.  You can then use all the usual @value{GDBN} commands.

For example, this sequence connects to the target board through a serial
port, and loads and runs a program called @var{prog} through the
debugger:

@example
host$ @value{GDBP} @var{prog}
GDB is free software and @dots{}
(gdb) target mips /dev/ttyb
(gdb) load @var{prog}
(gdb) run
@end example

@item target mips @var{hostname}:@var{portnumber}
On some @value{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
@samp{@var{hostname}:@var{portnumber}}.
@end table

@noindent
@value{GDBN} also supports these special commands for MIPS targets:

@table @code
@item set mipsfpu double
@itemx set mipsfpu single
@itemx set mipsfpu none
@itemx show mipsfpu
@kindex set mipsfpu
@kindex show mipsfpu
@cindex MIPS remote floating point
@cindex floating point, MIPS remote
If your target board does not support the MIPS floating point
coprocessor, you should use the command @samp{set mipsfpu none} (if you
need this, you may wish to put the command in your @value{GDBINIT}
file).  This tells @value{GDBN} how to find the return value of
functions which return floating point values.  It also allows
@value{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 @sc{r4650}
processor, use the command @samp{set mipsfpu single}.  The default
double precision floating point coprocessor may be selected using
@samp{set mipsfpu double}.

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

As usual, you can inquire about the @code{mipsfpu} variable with
@samp{show mipsfpu}.

@item set remotedebug @var{n}
@itemx show remotedebug
@kindex set remotedebug
@kindex show remotedebug
@cindex @code{remotedebug}, MIPS protocol
@cindex MIPS @code{remotedebug} protocol
@c FIXME! For this to be useful, you must know something about the MIPS
@c FIXME...protocol.  Where is it described?
You can see some debugging information about communications with the board
by setting the @code{remotedebug} variable.  If you set it to @code{1} using
@samp{set remotedebug 1}, every packet is displayed.  If you set it
to @code{2}, every character is displayed.  You can check the current value
at any time with the command @samp{show remotedebug}.

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

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

@ifset SIMS
@node Simulator
@subsection Simulated CPU target

@ifset GENERIC
@cindex simulator
@cindex simulator, Z8000
@cindex Z8000 simulator
@cindex simulator, H8/300 or H8/500
@cindex H8/300 or H8/500 simulator
@cindex simulator, Hitachi SH
@cindex Hitachi SH simulator
@cindex CPU simulator
For some configurations, @value{GDBN} includes a CPU simulator that you
can use instead of a hardware CPU to debug your programs.  Currently,
a simulator is available when @value{GDBN} is configured to debug Zilog
Z8000 or Hitachi microprocessor targets.
@end ifset

@ifclear GENERIC
@ifset H8
@cindex simulator, H8/300 or H8/500
@cindex Hitachi H8/300 or H8/500 simulator
@cindex simulator, Hitachi SH
@cindex Hitachi SH simulator
When configured for debugging Hitachi microprocessor targets,
@value{GDBN} includes a CPU simulator for the target chip (a Hitachi SH,
H8/300, or H8/500).
@end ifset

@ifset Z8K
@cindex simulator, Z8000
@cindex Zilog Z8000 simulator
When configured for debugging Zilog Z8000 targets, @value{GDBN} includes
a Z8000 simulator.
@end ifset
@end ifclear

@ifset Z8K
For the Z8000 family, @samp{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.
@end ifset

@table @code
@item target sim
@kindex sim
@kindex target sim
Debug programs on a simulated CPU 
@ifset GENERIC
(which CPU depends on the @value{GDBN} configuration)
@end ifset
@end table

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

As well as making available all the usual machine registers (see
@code{info reg}), this debugging target provides three additional items
of information as specially named registers:

@table @code
@item cycles
Counts clock-ticks in the simulator.

@item insts
Counts instructions run in the simulator.

@item time
Execution time in 60ths of a second. 
@end table

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