* remote.c, remote-utils.c: Use SERIAL_FLUSH_INPUT after opening it.

[deliverable/binutils-gdb.git] / gdb / remote.c

/* Remote target communications for serial-line targets in custom GDB protocol
   Copyright 1988, 1991, 1992, 1993 Free Software Foundation, Inc.

This file is part of GDB.

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */

/* Remote communication protocol.

   A debug packet whose contents are <data>
   is encapsulated for transmission in the form:

	$ <data> # CSUM1 CSUM2

	<data> must be ASCII alphanumeric and cannot include characters
	'$' or '#'

	CSUM1 and CSUM2 are ascii hex representation of an 8-bit 
	checksum of <data>, the most significant nibble is sent first.
	the hex digits 0-9,a-f are used.

   Receiver responds with:

	+	- if CSUM is correct and ready for next packet
	-	- if CSUM is incorrect

   <data> is as follows:
   All values are encoded in ascii hex digits.

	Request		Packet

	read registers  g
	reply		XX....X		Each byte of register data
					is described by two hex digits.
					Registers are in the internal order
					for GDB, and the bytes in a register
					are in the same order the machine uses.
			or ENN		for an error.

	write regs	GXX..XX		Each byte of register data
					is described by two hex digits.
	reply		OK		for success
			ENN		for an error

	read mem	mAA..AA,LLLL	AA..AA is address, LLLL is length.
	reply		XX..XX		XX..XX is mem contents
					Can be fewer bytes than requested
					if able to read only part of the data.
			or ENN		NN is errno

	write mem	MAA..AA,LLLL:XX..XX
					AA..AA is address,
					LLLL is number of bytes,
					XX..XX is data
	reply		OK		for success
			ENN		for an error (this includes the case
					where only part of the data was
					written).

	cont		cAA..AA		AA..AA is address to resume
					If AA..AA is omitted,
					resume at same address.

	step		sAA..AA		AA..AA is address to resume
					If AA..AA is omitted,
					resume at same address.

	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.

	There is no immediate reply to step or cont.
	The reply comes when the machine stops.
	It is		SAA		AA is the "signal number"

	or...		TAAn...:r...;n:r...;n...:r...;
					AA = signal number
					n... = register number
					r... = register contents
	or...		WAA		The process extited, and AA is
					the exit status.  This is only
					applicable for certains sorts of
					targets.
	or...		NAATT;DD;BB	Relocate the object file.
					AA = signal number
					TT = text address
					DD = data address
					BB = bss address
					This is used by the NLM stub,
					which is why it only has three
					addresses rather than one per
					section: the NLM stub always
					sees only three sections, even
					though gdb may see more.

	kill request	k

	toggle debug	d		toggle debug flag (see 386 & 68k stubs)
	reset		r		reset -- see sparc stub.
	reserved	<other>		On other requests, the stub should
					ignore the request and send an empty
					response ($#<checksum>).  This way
					we can extend the protocol and GDB
					can tell whether the stub it is
					talking to uses the old or the new.
*/

#include "defs.h"
#include <string.h>
#include <fcntl.h>
#include "frame.h"
#include "inferior.h"
#include "bfd.h"
#include "symfile.h"
#include "target.h"
#include "wait.h"
#include "terminal.h"
#include "gdbcmd.h"
#include "objfiles.h"
#include "gdb-stabs.h"

#include "dcache.h"
#include "remote-utils.h"

#if !defined(DONT_USE_REMOTE)
#ifdef USG
#include <sys/types.h>
#endif

#include <signal.h>
#include "serial.h"

/* Prototypes for local functions */

static int
remote_write_bytes PARAMS ((CORE_ADDR memaddr, unsigned char *myaddr, int len));

static int
remote_read_bytes PARAMS ((CORE_ADDR memaddr, unsigned char *myaddr, int len));

static void
remote_files_info PARAMS ((struct target_ops *ignore));

static int
remote_xfer_memory PARAMS ((CORE_ADDR memaddr, char *myaddr, int len,
			    int should_write, struct target_ops *target));

static void 
remote_prepare_to_store PARAMS ((void));

static void
remote_fetch_registers PARAMS ((int regno));

static void
remote_resume PARAMS ((int pid, int step, int siggnal));

static int
remote_start_remote PARAMS ((char *dummy));

static void
remote_open PARAMS ((char *name, int from_tty));

static void
remote_close PARAMS ((int quitting));

static void
remote_store_registers PARAMS ((int regno));

static void
getpkt PARAMS ((char *buf, int forever));

static void
putpkt PARAMS ((char *buf));

static void
remote_send PARAMS ((char *buf));

static int
readchar PARAMS ((void));

static int
remote_wait PARAMS ((WAITTYPE *status));

static int
tohex PARAMS ((int nib));

static int
fromhex PARAMS ((int a));

static void
remote_detach PARAMS ((char *args, int from_tty));

static void
remote_interrupt PARAMS ((int signo));

static void
remote_interrupt_twice PARAMS ((int signo));

extern struct target_ops remote_ops;	/* Forward decl */

/* This was 5 seconds, which is a long time to sit and wait.
   Unless this is going though some terminal server or multiplexer or
   other form of hairy serial connection, I would think 2 seconds would
   be plenty.  */
static int timeout = 2;

#if 0
int icache;
#endif

/* Descriptor for I/O to remote machine.  Initialize it to NULL so that
   remote_open knows that we don't have a file open when the program
   starts.  */
serial_t remote_desc = NULL;

#define	PBUFSIZ	1024

/* Maximum number of bytes to read/write at once.  The value here
   is chosen to fill up a packet (the headers account for the 32).  */
#define MAXBUFBYTES ((PBUFSIZ-32)/2)

/* Round up PBUFSIZ to hold all the registers, at least.  */
#if REGISTER_BYTES > MAXBUFBYTES
#undef	PBUFSIZ
#define	PBUFSIZ	(REGISTER_BYTES * 2 + 32)
#endif
\f
/* Clean up connection to a remote debugger.  */

/* ARGSUSED */
static void
remote_close (quitting)
     int quitting;
{
  if (remote_desc)
    SERIAL_CLOSE (remote_desc);
  remote_desc = NULL;
}

/* Stub for catch_errors.  */

static int
remote_start_remote (dummy)
     char *dummy;
{
  immediate_quit = 1;		/* Allow user to interrupt it */

  /* Ack any packet which the remote side has already sent.  */
  /* I'm not sure this \r is needed; we don't use it any other time we
     send an ack.  */
  SERIAL_WRITE (remote_desc, "+\r", 2);
  putpkt ("?");			/* initiate a query from remote machine */
  immediate_quit = 0;

  start_remote ();		/* Initialize gdb process mechanisms */
  return 1;
}

/* Open a connection to a remote debugger.
   NAME is the filename used for communication.  */

static DCACHE *remote_dcache;

static void
remote_open (name, from_tty)
     char *name;
     int from_tty;
{
  if (name == 0)
    error (
"To open a remote debug connection, you need to specify what serial\n\
device is attached to the remote system (e.g. /dev/ttya).");

  target_preopen (from_tty);

  unpush_target (&remote_ops);

  remote_dcache = dcache_init (remote_read_bytes, remote_write_bytes);

  remote_desc = SERIAL_OPEN (name);
  if (!remote_desc)
    perror_with_name (name);

  if (SERIAL_SETBAUDRATE (remote_desc, sr_get_baud_rate()))
    {
      SERIAL_CLOSE (remote_desc);
      perror_with_name (name);
    }

  SERIAL_RAW (remote_desc);

  /* If there is something sitting in the buffer we might take it as a
     response to a command, which would be bad.  */
  SERIAL_FLUSH_INPUT (remote_desc);

  if (from_tty)
    {
      puts_filtered ("Remote debugging using ");
      puts_filtered (name);
      puts_filtered ("\n");
    }
  push_target (&remote_ops);	/* Switch to using remote target now */

  /* Start the remote connection; if error (0), discard this target.
     In particular, if the user quits, be sure to discard it
     (we'd be in an inconsistent state otherwise).  */
  if (!catch_errors (remote_start_remote, (char *)0, 
	"Couldn't establish connection to remote target\n", RETURN_MASK_ALL))
    pop_target();
}

/* remote_detach()
   takes a program previously attached to and detaches it.
   We better not have left any breakpoints
   in the program or it'll die when it hits one.
   Close the open connection to the remote debugger.
   Use this when you want to detach and do something else
   with your gdb.  */

static void
remote_detach (args, from_tty)
     char *args;
     int from_tty;
{
  if (args)
    error ("Argument given to \"detach\" when remotely debugging.");
  
  pop_target ();
  if (from_tty)
    puts_filtered ("Ending remote debugging.\n");
}

/* Convert hex digit A to a number.  */

static int
fromhex (a)
     int a;
{
  if (a >= '0' && a <= '9')
    return a - '0';
  else if (a >= 'a' && a <= 'f')
    return a - 'a' + 10;
  else
    error ("Reply contains invalid hex digit");
  return -1;
}

/* Convert number NIB to a hex digit.  */

static int
tohex (nib)
     int nib;
{
  if (nib < 10)
    return '0'+nib;
  else
    return 'a'+nib-10;
}
\f
/* Tell the remote machine to resume.  */

static void
remote_resume (pid, step, siggnal)
     int pid, step, siggnal;
{
  char buf[PBUFSIZ];

  if (siggnal)
    {
      char *name;
      target_terminal_ours_for_output ();
      printf_filtered ("Can't send signals to a remote system.  ");
      name = strsigno (siggnal);
      if (name)
	printf_filtered (name);
      else
	printf_filtered ("Signal %d", siggnal);
      printf_filtered (" not sent.\n");
      target_terminal_inferior ();
    }

  dcache_flush (remote_dcache);

  strcpy (buf, step ? "s": "c");

  putpkt (buf);
}
\f
/* Send ^C to target to halt it.  Target will respond, and send us a
   packet.  */

static void
remote_interrupt (signo)
     int signo;
{
  /* If this doesn't work, try more severe steps.  */
  signal (signo, remote_interrupt_twice);
  
  if (sr_get_debug ())
    printf ("remote_interrupt called\n");

  SERIAL_WRITE (remote_desc, "\003", 1); /* Send a ^C */
}

static void (*ofunc)();

/* The user typed ^C twice.  */
static void
remote_interrupt_twice (signo)
     int signo;
{
  signal (signo, ofunc);
  
  target_terminal_ours ();
  if (query ("Interrupted while waiting for the program.\n\
Give up (and stop debugging it)? "))
    {
      target_mourn_inferior ();
      return_to_top_level (RETURN_QUIT);
    }
  else
    {
      signal (signo, remote_interrupt);
      target_terminal_inferior ();
    }
}

/* Wait until the remote machine stops, then return,
   storing status in STATUS just as `wait' would.
   Returns "pid" (though it's not clear what, if anything, that
   means in the case of this target).  */

static int
remote_wait (status)
     WAITTYPE *status;
{
  unsigned char buf[PBUFSIZ];

  WSETEXIT ((*status), 0);

  while (1)
    {
      unsigned char *p;

      ofunc = (void (*)()) signal (SIGINT, remote_interrupt);
      getpkt ((char *) buf, 1);
      signal (SIGINT, ofunc);

      if (buf[0] == 'E')
	warning ("Remote failure reply: %s", buf);
      else if (buf[0] == 'T')
	{
	  int i;
	  long regno;
	  char regs[MAX_REGISTER_RAW_SIZE];

	  /* Expedited reply, containing Signal, {regno, reg} repeat */
	  /*  format is:  'Tssn...:r...;n...:r...;n...:r...;#cc', where
	      ss = signal number
	      n... = register number
	      r... = register contents
	      */

	  p = &buf[3];		/* after Txx */

	  while (*p)
	    {
	      unsigned char *p1;

	      regno = strtol (p, &p1, 16); /* Read the register number */

	      if (p1 == p)
		warning ("Remote sent badly formed register number: %s\nPacket: '%s'\n",
			 p1, buf);

	      p = p1;

	      if (*p++ != ':')
		warning ("Malformed packet (missing colon): %s\nPacket: '%s'\n",
			 p, buf);

	      if (regno >= NUM_REGS)
		warning ("Remote sent bad register number %d: %s\nPacket: '%s'\n",
			 regno, p, buf);

	      for (i = 0; i < REGISTER_RAW_SIZE (regno); i++)
		{
		  if (p[0] == 0 || p[1] == 0)
		    warning ("Remote reply is too short: %s", buf);
		  regs[i] = fromhex (p[0]) * 16 + fromhex (p[1]);
		  p += 2;
		}

	      if (*p++ != ';')
		warning ("Remote register badly formatted: %s", buf);

	      supply_register (regno, regs);
	    }
	  break;
	}
      else if (buf[0] == 'N')
	{
	  unsigned char *p1;
	  bfd_vma text_addr, data_addr, bss_addr;

	  /* Relocate object file.  Format is NAATT;DD;BB where AA is
	     the signal number, TT is the new text address, DD is the
	     new data address, and BB is the new bss address.  This is
	     used by the NLM stub; gdb may see more sections.  */
	  p = &buf[3];
	  text_addr = strtol (p, &p1, 16);
	  if (p1 == p || *p1 != ';')
	    warning ("Malformed relocation packet: Packet '%s'", buf);
	  p = p1 + 1;
	  data_addr = strtol (p, &p1, 16);
	  if (p1 == p || *p1 != ';')
	    warning ("Malformed relocation packet: Packet '%s'", buf);
	  p = p1 + 1;
	  bss_addr = strtol (p, &p1, 16);
	  if (p1 == p)
	    warning ("Malformed relocation packet: Packet '%s'", buf);

	  if (symfile_objfile != NULL)
	    {
	      struct section_offsets *offs;

	      /* FIXME: This code assumes gdb-stabs.h is being used;
		 it's broken for xcoff, dwarf, sdb-coff, etc.  But
		 there is no simple canonical representation for this
		 stuff.  (Just what does "text" as seen by the stub
		 mean, anyway?).  */

	      /* FIXME: Why don't the various symfile_offsets routines
		 in the sym_fns vectors set this?
		 (no good reason -kingdon).  */
	      if (symfile_objfile->num_sections == 0)
		symfile_objfile->num_sections = SECT_OFF_MAX;

	      offs = ((struct section_offsets *)
		      alloca (sizeof (struct section_offsets)
			      + (symfile_objfile->num_sections
				 * sizeof (offs->offsets))));
	      memcpy (offs, symfile_objfile->section_offsets,
		      (sizeof (struct section_offsets)
		       + (symfile_objfile->num_sections
			  * sizeof (offs->offsets))));
	      ANOFFSET (offs, SECT_OFF_TEXT) = text_addr;
	      ANOFFSET (offs, SECT_OFF_DATA) = data_addr;
	      ANOFFSET (offs, SECT_OFF_BSS) = bss_addr;

	      objfile_relocate (symfile_objfile, offs);
	    }
	  break;
	}
      else if (buf[0] == 'W')
	{
	  /* The remote process exited.  */
	  WSETEXIT (*status, (fromhex (buf[1]) << 4) + fromhex (buf[2]));
	  return 0;
	}
      else if (buf[0] == 'S')
	break;
      else
	warning ("Invalid remote reply: %s", buf);
    }

  WSETSTOP ((*status), (((fromhex (buf[1])) << 4) + (fromhex (buf[2]))));

  return 0;
}

/* Number of bytes of registers this stub implements.  */
static int register_bytes_found;

/* Read the remote registers into the block REGS.  */
/* Currently we just read all the registers, so we don't use regno.  */
/* ARGSUSED */
static void
remote_fetch_registers (regno)
     int regno;
{
  char buf[PBUFSIZ];
  int i;
  char *p;
  char regs[REGISTER_BYTES];

  sprintf (buf, "g");
  remote_send (buf);

  /* Unimplemented registers read as all bits zero.  */
  memset (regs, 0, REGISTER_BYTES);

  /* Reply describes registers byte by byte, each byte encoded as two
     hex characters.  Suck them all up, then supply them to the
     register cacheing/storage mechanism.  */

  p = buf;
  for (i = 0; i < REGISTER_BYTES; i++)
    {
      if (p[0] == 0)
	break;
      if (p[1] == 0)
	{
	  warning ("Remote reply is of odd length: %s", buf);
	  /* Don't change register_bytes_found in this case, and don't
	     print a second warning.  */
	  goto supply_them;
	}
      regs[i] = fromhex (p[0]) * 16 + fromhex (p[1]);
      p += 2;
    }

  if (i != register_bytes_found)
    {
      register_bytes_found = i;
#ifdef REGISTER_BYTES_OK
      if (!REGISTER_BYTES_OK (i))
	warning ("Remote reply is too short: %s", buf);
#endif
    }

 supply_them:
  for (i = 0; i < NUM_REGS; i++)
    supply_register (i, &regs[REGISTER_BYTE(i)]);
}

/* Prepare to store registers.  Since we send them all, we have to
   read out the ones we don't want to change first.  */

static void 
remote_prepare_to_store ()
{
  /* Make sure the entire registers array is valid.  */
  read_register_bytes (0, (char *)NULL, REGISTER_BYTES);
}

/* Store the remote registers from the contents of the block REGISTERS. 
   FIXME, eventually just store one register if that's all that is needed.  */

/* ARGSUSED */
static void
remote_store_registers (regno)
     int regno;
{
  char buf[PBUFSIZ];
  int i;
  char *p;

  buf[0] = 'G';
  
  /* Command describes registers byte by byte,
     each byte encoded as two hex characters.  */

  p = buf + 1;
  /* remote_prepare_to_store insures that register_bytes_found gets set.  */
  for (i = 0; i < register_bytes_found; i++)
    {
      *p++ = tohex ((registers[i] >> 4) & 0xf);
      *p++ = tohex (registers[i] & 0xf);
    }
  *p = '\0';

  remote_send (buf);
}

#if 0

/* Use of the data cache is disabled because it loses for looking at
   and changing hardware I/O ports and the like.  Accepting `volatile'
   would perhaps be one way to fix it, but a better way which would
   win for more cases would be to use the executable file for the text
   segment, like the `icache' code below but done cleanly (in some
   target-independent place, perhaps in target_xfer_memory, perhaps
   based on assigning each target a speed or perhaps by some simpler
   mechanism).  */

/* Read a word from remote address ADDR and return it.
   This goes through the data cache.  */

static int
remote_fetch_word (addr)
     CORE_ADDR addr;
{
#if 0
  if (icache)
    {
      extern CORE_ADDR text_start, text_end;

      if (addr >= text_start && addr < text_end)
	{
	  int buffer;
	  xfer_core_file (addr, &buffer, sizeof (int));
	  return buffer;
	}
    }
#endif
  return dcache_fetch (remote_dcache, addr);
}

/* Write a word WORD into remote address ADDR.
   This goes through the data cache.  */

static void
remote_store_word (addr, word)
     CORE_ADDR addr;
     int word;
{
  dcache_poke (remote_dcache, addr, word);
}
#endif /* 0 */
\f
/* Write memory data directly to the remote machine.
   This does not inform the data cache; the data cache uses this.
   MEMADDR is the address in the remote memory space.
   MYADDR is the address of the buffer in our space.
   LEN is the number of bytes.

   Returns number of bytes transferred, or 0 for error.  */

static int
remote_write_bytes (memaddr, myaddr, len)
     CORE_ADDR memaddr;
     unsigned char *myaddr;
     int len;
{
  char buf[PBUFSIZ];
  int i;
  char *p;

  if (len > PBUFSIZ / 2 - 20)
    abort ();

  sprintf (buf, "M%x,%x:", memaddr, len);

  /* We send target system values byte by byte, in increasing byte addresses,
     each byte encoded as two hex characters.  */

  p = buf + strlen (buf);
  for (i = 0; i < len; i++)
    {
      *p++ = tohex ((myaddr[i] >> 4) & 0xf);
      *p++ = tohex (myaddr[i] & 0xf);
    }
  *p = '\0';

  putpkt (buf);
  getpkt (buf, 0);

  if (buf[0] == 'E')
    {
      /* There is no correspondance between what the remote protocol uses
	 for errors and errno codes.  We would like a cleaner way of
	 representing errors (big enough to include errno codes, bfd_error
	 codes, and others).  But for now just return EIO.  */
      errno = EIO;
      return 0;
    }
  return len;
}

/* Read memory data directly from the remote machine.
   This does not use the data cache; the data cache uses this.
   MEMADDR is the address in the remote memory space.
   MYADDR is the address of the buffer in our space.
   LEN is the number of bytes.

   Returns number of bytes transferred, or 0 for error.  */

static int
remote_read_bytes (memaddr, myaddr, len)
     CORE_ADDR memaddr;
     unsigned char *myaddr;
     int len;
{
  char buf[PBUFSIZ];
  int i;
  char *p;

  if (len > PBUFSIZ / 2 - 1)
    abort ();

  sprintf (buf, "m%x,%x", memaddr, len);
  putpkt (buf);
  getpkt (buf, 0);

  if (buf[0] == 'E')
    {
      /* There is no correspondance between what the remote protocol uses
	 for errors and errno codes.  We would like a cleaner way of
	 representing errors (big enough to include errno codes, bfd_error
	 codes, and others).  But for now just return EIO.  */
      errno = EIO;
      return 0;
    }

  /* Reply describes memory byte by byte,
     each byte encoded as two hex characters.  */

  p = buf;
  for (i = 0; i < len; i++)
    {
      if (p[0] == 0 || p[1] == 0)
	/* Reply is short.  This means that we were able to read only part
	   of what we wanted to.  */
	break;
      myaddr[i] = fromhex (p[0]) * 16 + fromhex (p[1]);
      p += 2;
    }
  return i;
}
\f
/* Read or write LEN bytes from inferior memory at MEMADDR, transferring
   to or from debugger address MYADDR.  Write to inferior if SHOULD_WRITE is
   nonzero.  Returns length of data written or read; 0 for error.  */

/* ARGSUSED */
static int
remote_xfer_memory(memaddr, myaddr, len, should_write, target)
     CORE_ADDR memaddr;
     char *myaddr;
     int len;
     int should_write;
     struct target_ops *target;			/* ignored */
{
  int xfersize;
  int bytes_xferred;
  int total_xferred = 0;

  while (len > 0)
    {
      if (len > MAXBUFBYTES)
	xfersize = MAXBUFBYTES;
      else
	xfersize = len;

      if (should_write)
        bytes_xferred = remote_write_bytes (memaddr, myaddr, xfersize);
      else
	bytes_xferred = remote_read_bytes (memaddr, myaddr, xfersize);

      /* If we get an error, we are done xferring.  */
      if (bytes_xferred == 0)
	break;

      memaddr += bytes_xferred;
      myaddr  += bytes_xferred;
      len     -= bytes_xferred;
      total_xferred += bytes_xferred;
    }
  return total_xferred;
}

static void
remote_files_info (ignore)
     struct target_ops *ignore;
{
  puts_filtered ("Debugging a target over a serial line.\n");
}
\f
/* Stuff for dealing with the packets which are part of this protocol.
   See comment at top of file for details.  */

/* Read a single character from the remote end, masking it down to 7 bits. */

static int
readchar ()
{
  int ch;

  ch = SERIAL_READCHAR (remote_desc, timeout);

  if (ch < 0)
    return ch;

  return ch & 0x7f;
}

/* Send the command in BUF to the remote machine,
   and read the reply into BUF.
   Report an error if we get an error reply.  */

static void
remote_send (buf)
     char *buf;
{

  putpkt (buf);
  getpkt (buf, 0);

  if (buf[0] == 'E')
    error ("Remote failure reply: %s", buf);
}

/* Send a packet to the remote machine, with error checking.
   The data of the packet is in BUF.  */

static void
putpkt (buf)
     char *buf;
{
  int i;
  unsigned char csum = 0;
  char buf2[PBUFSIZ];
  int cnt = strlen (buf);
  int ch;
  char *p;

  /* Copy the packet into buffer BUF2, encapsulating it
     and giving it a checksum.  */

  if (cnt > sizeof(buf2) - 5)		/* Prosanity check */
    abort();

  p = buf2;
  *p++ = '$';

  for (i = 0; i < cnt; i++)
    {
      csum += buf[i];
      *p++ = buf[i];
    }
  *p++ = '#';
  *p++ = tohex ((csum >> 4) & 0xf);
  *p++ = tohex (csum & 0xf);

  /* Send it over and over until we get a positive ack.  */

  while (1)
    {
      if (sr_get_debug ())
	{
	  *p = '\0';
	  printf ("Sending packet: %s...", buf2);  fflush(stdout);
	}
      if (SERIAL_WRITE (remote_desc, buf2, p - buf2))
	perror_with_name ("putpkt: write failed");

      /* read until either a timeout occurs (-2) or '+' is read */
      while (1)
	{
	  ch = readchar ();

	  switch (ch)
	    {
	    case '+':
	      if (sr_get_debug ())
		printf("Ack\n");
	      return;
	    case SERIAL_TIMEOUT:
	      break;		/* Retransmit buffer */
	    case SERIAL_ERROR:
	      perror_with_name ("putpkt: couldn't read ACK");
	    case SERIAL_EOF:
	      error ("putpkt: EOF while trying to read ACK");
	    default:
	      if (sr_get_debug ())
		printf ("%02X %c ", ch&0xFF, ch);
	      continue;
	    }
	  break;		/* Here to retransmit */
	}
    }
}

/* Read a packet from the remote machine, with error checking,
   and store it in BUF.  BUF is expected to be of size PBUFSIZ.
   If FOREVER, wait forever rather than timing out; this is used
   while the target is executing user code.  */

static void
getpkt (buf, forever)
     char *buf;
     int forever;
{
  char *bp;
  unsigned char csum;
  int c = 0;
  unsigned char c1, c2;
  int retries = 0;
#define MAX_RETRIES	10

  while (1)
    {
      /* This can loop forever if the remote side sends us characters
	 continuously, but if it pauses, we'll get a zero from readchar
	 because of timeout.  Then we'll count that as a retry.  */

      c = readchar();
      if (c > 0 && c != '$')
	continue;

      if (c == SERIAL_TIMEOUT)
	{
	  if (forever)
	    continue;
	  if (++retries >= MAX_RETRIES)
	    if (sr_get_debug ()) puts_filtered ("Timed out.\n");
	  goto out;
	}

      if (c == SERIAL_EOF)
	error ("Remote connection closed");
      if (c == SERIAL_ERROR)
	perror_with_name ("Remote communication error");

      /* Force csum to be zero here because of possible error retry.  */
      csum = 0;
      bp = buf;

      while (1)
	{
	  c = readchar ();
	  if (c == SERIAL_TIMEOUT)
	    {
	      if (sr_get_debug ())
		puts_filtered ("Timeout in mid-packet, retrying\n");
	      goto whole;		/* Start a new packet, count retries */
	    } 
	  if (c == '$')
	    {
	      if (sr_get_debug ())
		puts_filtered ("Saw new packet start in middle of old one\n");
	      goto whole;		/* Start a new packet, count retries */
	    }
	  if (c == '#')
	    break;
	  if (bp >= buf+PBUFSIZ-1)
	  {
	    *bp = '\0';
	    puts_filtered ("Remote packet too long: ");
	    puts_filtered (buf);
	    puts_filtered ("\n");
	    goto whole;
	  }
	  *bp++ = c;
	  csum += c;
	}
      *bp = 0;

      c1 = fromhex (readchar ());
      c2 = fromhex (readchar ());
      if ((csum & 0xff) == (c1 << 4) + c2)
	break;
      printf_filtered ("Bad checksum, sentsum=0x%x, csum=0x%x, buf=",
	      (c1 << 4) + c2, csum & 0xff);
      puts_filtered (buf);
      puts_filtered ("\n");

      /* Try the whole thing again.  */
whole:
      if (++retries < MAX_RETRIES)
	{
	  SERIAL_WRITE (remote_desc, "-", 1);
	}
      else
	{
	  printf ("Ignoring packet error, continuing...\n");
	  break;
	}
    }

out:

  SERIAL_WRITE (remote_desc, "+", 1);

  if (sr_get_debug ())
    fprintf (stderr,"Packet received: %s\n", buf);
}
\f
static void
remote_kill ()
{
  putpkt ("k");
  /* Don't wait for it to die.  I'm not really sure it matters whether
     we do or not.  For the existing stubs, kill is a noop.  */
  target_mourn_inferior ();
}

static void
remote_mourn ()
{
  unpush_target (&remote_ops);
  generic_mourn_inferior ();
}
\f
#ifdef REMOTE_BREAKPOINT

/* On some machines, e.g. 68k, we may use a different breakpoint instruction
   than other targets.  */
static unsigned char break_insn[] = REMOTE_BREAKPOINT;

/* Check that it fits in BREAKPOINT_MAX bytes.  */
static unsigned char check_break_insn_size[BREAKPOINT_MAX] = REMOTE_BREAKPOINT;

#else /* No REMOTE_BREAKPOINT.  */

/* Same old breakpoint instruction.  This code does nothing different
   than mem-break.c.  */
static unsigned char break_insn[] = BREAKPOINT;

#endif /* No REMOTE_BREAKPOINT.  */

/* Insert a breakpoint on targets that don't have any better breakpoint
   support.  We read the contents of the target location and stash it,
   then overwrite it with a breakpoint instruction.  ADDR is the target
   location in the target machine.  CONTENTS_CACHE is a pointer to 
   memory allocated for saving the target contents.  It is guaranteed
   by the caller to be long enough to save sizeof BREAKPOINT bytes (this
   is accomplished via BREAKPOINT_MAX).  */

static int
remote_insert_breakpoint (addr, contents_cache)
     CORE_ADDR addr;
     char *contents_cache;
{
  int val;

  val = target_read_memory (addr, contents_cache, sizeof break_insn);

  if (val == 0)
    val = target_write_memory (addr, (char *)break_insn, sizeof break_insn);

  return val;
}

static int
remote_remove_breakpoint (addr, contents_cache)
     CORE_ADDR addr;
     char *contents_cache;
{
  return target_write_memory (addr, contents_cache, sizeof break_insn);
}
\f
/* Define the target subroutine names */

struct target_ops remote_ops = {
  "remote",			/* to_shortname */
  "Remote serial target in gdb-specific protocol",	/* to_longname */
  "Use a remote computer via a serial line, using a gdb-specific protocol.\n\
Specify the serial device it is connected to (e.g. /dev/ttya).",  /* to_doc */
  remote_open,			/* to_open */
  remote_close,			/* to_close */
  NULL,				/* to_attach */
  remote_detach,		/* to_detach */
  remote_resume,		/* to_resume */
  remote_wait,			/* to_wait */
  remote_fetch_registers,	/* to_fetch_registers */
  remote_store_registers,	/* to_store_registers */
  remote_prepare_to_store,	/* to_prepare_to_store */
  remote_xfer_memory,		/* to_xfer_memory */
  remote_files_info,		/* to_files_info */

  remote_insert_breakpoint,	/* to_insert_breakpoint */
  remote_remove_breakpoint,	/* to_remove_breakpoint */

  NULL,				/* to_terminal_init */
  NULL,				/* to_terminal_inferior */
  NULL,				/* to_terminal_ours_for_output */
  NULL,				/* to_terminal_ours */
  NULL,				/* to_terminal_info */
  remote_kill,			/* to_kill */
  generic_load,			/* to_load */
  NULL,				/* to_lookup_symbol */
  NULL,				/* to_create_inferior */
  remote_mourn,			/* to_mourn_inferior */
  0,				/* to_can_run */
  0,				/* to_notice_signals */
  process_stratum,		/* to_stratum */
  NULL,				/* to_next */
  1,				/* to_has_all_memory */
  1,				/* to_has_memory */
  1,				/* to_has_stack */
  1,				/* to_has_registers */
  1,				/* to_has_execution */
  NULL,				/* sections */
  NULL,				/* sections_end */
  OPS_MAGIC			/* to_magic */
};

void
_initialize_remote ()
{
  add_target (&remote_ops);
}
#endif