Checkpoint. Runs "hello, world", sets breakpoints, isn't too graceful

about program termination.

This file probably should not be part of gdb 4.8, although it wouldn't
do any actual harm.  Not yet added to .Sanitize.

1 files changed, 1246 insertions, 0 deletions

diff --git a/gdb/remote-mips.c b/gdb/remote-mips.c
new file mode 100644
index 0000000..6c559f1
--- /dev/null
+++ b/gdb/remote-mips.c
@@ -0,0 +1,1246 @@
+/* Remote debugging interface for MIPS remote debugging protocol.
+   Copyright 1993 Free Software Foundation, Inc.
+   Contributed by Cygnus Support.  Written by Ian Lance Taylor
+   <ian@cygnus.com>.
+
+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.  */
+
+#include "defs.h"
+#include "inferior.h"
+#include "bfd.h"
+#include "wait.h"
+#include "gdbcmd.h"
+#include "gdbcore.h"
+#include "serial.h"
+#include "target.h"
+
+#include <signal.h>
+
+/* Prototypes for local functions.  */
+
+static int
+mips_readchar PARAMS ((int timeout));
+
+static int
+mips_receive_header PARAMS ((unsigned char *hdr, int *pgarbage, int ch,
+			     int timeout));
+
+static int
+mips_receive_trailer PARAMS ((unsigned char *trlr, int *pgarbage, int *pch,
+			      int timeout));
+
+static int mips_cksum PARAMS ((const unsigned char *hdr,
+			       const unsigned char *data,
+			       int len));
+
+static void
+mips_send_packet PARAMS ((const char *s));
+
+static int
+mips_receive_packet PARAMS ((char *buff));
+
+static int
+mips_request PARAMS ((char cmd, unsigned int addr, unsigned int data,
+		      int *perr));
+
+static void
+mips_open PARAMS ((char *name, int from_tty));
+
+static void
+mips_close PARAMS ((int quitting));
+
+static void
+mips_detach PARAMS ((char *args, int from_tty));
+
+static void
+mips_resume PARAMS ((int step, int siggnal));
+
+static int
+mips_wait PARAMS ((WAITTYPE *status));
+
+static int
+mips_map_regno PARAMS ((int regno));
+
+static void
+mips_fetch_registers PARAMS ((int regno));
+
+static void
+mips_prepare_to_store PARAMS ((void));
+
+static void
+mips_store_registers PARAMS ((int regno));
+
+static int
+mips_fetch_word PARAMS ((CORE_ADDR addr));
+
+static void
+mips_store_word PARAMS ((CORE_ADDR addr, int value));
+
+static int
+mips_xfer_memory PARAMS ((CORE_ADDR memaddr, char *myaddr, int len,
+			  int write, struct target_ops *ignore));
+
+static void
+mips_files_info PARAMS ((struct target_ops *ignore));
+
+static void
+mips_load PARAMS ((char *args, int from_tty));
+
+static void
+mips_create_inferior PARAMS ((char *execfile, char *args, char **env));
+
+static void
+mips_mourn_inferior PARAMS ((void));
+
+/* A forward declaration.  */
+extern struct target_ops mips_ops;
+
+/* The MIPS remote debugging interface is built on top of a simple
+   packet protocol.  Each packet is organized as follows:
+
+   SYN	The first character is always a SYN (ASCII 026, or ^V).  SYN
+	may not appear anywhere else in the packet.  Any time a SYN is
+	seen, a new packet should be assumed to have begun.
+
+   TYPE_LEN
+	This byte contains the upper five bits of the logical length
+	of the data section, plus a single bit indicating whether this
+	is a data packet or an acknowledgement.  The documentation
+	indicates that this bit is 1 for a data packet, but the actual
+	board uses 1 for an acknowledgement.  The value of the byte is
+		0x40 + (ack ? 0x20 : 0) + (len >> 6)
+	(we always have 0 <= len < 1024).  Acknowledgement packets do
+	not carry data, and must have a data length of 0.
+
+   LEN1 This byte contains the lower six bits of the logical length of
+	the data section.  The value is
+	 	0x40 + (len & 0x3f)
+
+   SEQ	This byte contains the six bit sequence number of the packet.
+	The value is
+		0x40 + seq
+	An acknowlegment packet contains the sequence number of the
+	packet being acknowledged plus 1 module 64.  Data packets are
+	transmitted in sequence.  There may only be one outstanding
+	unacknowledged data packet at a time.  The sequence numbers
+	are independent in each direction.  If an acknowledgement for
+	the previous packet is received (i.e., an acknowledgement with
+	the sequence number of the packet just sent) the packet just
+	sent should be retransmitted.  If no acknowledgement is
+	received within a timeout period, the packet should be
+	retransmitted.  This has an unfortunate failure condition on a
+	high-latency line, as a delayed acknowledgement may lead to an
+	endless series of duplicate packets.
+
+   DATA	The actual data bytes follow.  The following characters are
+	escaped inline with DLE (ASCII 020, or ^P):
+		SYN (026)	DLE S
+		DLE (020)	DLE D
+		^C  (003)	DLE C
+		^S  (023)	DLE s
+		^Q  (021)	DLE q
+	The additional DLE characters are not counted in the logical
+	length stored in the TYPE_LEN and LEN1 bytes.
+
+   CSUM1
+   CSUM2
+   CSUM3
+	These bytes contain an 18 bit checksum of the complete
+	contents of the packet excluding the SEQ byte and the
+	CSUM[123] bytes.  The checksum is simply the twos complement
+	addition of all the bytes treated as unsigned characters.  The
+	values of the checksum bytes are:
+		CSUM1: 0x40 + ((cksum >> 12) & 0x3f)
+		CSUM2: 0x40 + ((cksum >> 6) & 0x3f)
+		CSUM3: 0x40 + (cksum & 0x3f)
+
+   It happens that the MIPS remote debugging protocol always
+   communicates with ASCII strings.  Because of this, this
+   implementation doesn't bother to handle the DLE quoting mechanism,
+   since it will never be required.  */
+
+/* The SYN character which starts each packet.  */
+#define SYN '\026'
+
+/* The 0x40 used to offset each packet (this value ensures that all of
+   the header and trailer bytes, other than SYN, are printable ASCII
+   characters).  */
+#define HDR_OFFSET 0x40
+
+/* The indices of the bytes in the packet header.  */
+#define HDR_INDX_SYN 0
+#define HDR_INDX_TYPE_LEN 1
+#define HDR_INDX_LEN1 2
+#define HDR_INDX_SEQ 3
+#define HDR_LENGTH 4
+
+/* The data/ack bit in the TYPE_LEN header byte.  */
+#define TYPE_LEN_DA_BIT 0x20
+#define TYPE_LEN_DATA 0
+#define TYPE_LEN_ACK TYPE_LEN_DA_BIT
+
+/* How to compute the header bytes.  */
+#define HDR_SET_SYN(data, len, seq) (SYN)
+#define HDR_SET_TYPE_LEN(data, len, seq) \
+  (HDR_OFFSET \
+   + ((data) ? TYPE_LEN_DATA : TYPE_LEN_ACK) \
+   + (((len) >> 6) & 0x1f))
+#define HDR_SET_LEN1(data, len, seq) (HDR_OFFSET + ((len) & 0x3f))
+#define HDR_SET_SEQ(data, len, seq) (HDR_OFFSET + (seq))
+
+/* Check that a header byte is reasonable.  */
+#define HDR_CHECK(ch) (((ch) & HDR_OFFSET) == HDR_OFFSET)
+
+/* Get data from the header.  These macros evaluate their argument
+   multiple times.  */
+#define HDR_IS_DATA(hdr) \
+  (((hdr)[HDR_INDX_TYPE_LEN] & TYPE_LEN_DA_BIT) == TYPE_LEN_DATA)
+#define HDR_GET_LEN(hdr) \
+  ((((hdr)[HDR_INDX_TYPE_LEN] & 0x1f) << 6) + (((hdr)[HDR_INDX_LEN1] & 0x3f)))
+#define HDR_GET_SEQ(hdr) ((hdr)[HDR_INDX_SEQ] & 0x3f)
+
+/* The maximum data length.  */
+#define DATA_MAXLEN 1023
+
+/* The trailer offset.  */
+#define TRLR_OFFSET HDR_OFFSET
+
+/* The indices of the bytes in the packet trailer.  */
+#define TRLR_INDX_CSUM1 0
+#define TRLR_INDX_CSUM2 1
+#define TRLR_INDX_CSUM3 2
+#define TRLR_LENGTH 3
+
+/* How to compute the trailer bytes.  */
+#define TRLR_SET_CSUM1(cksum) (TRLR_OFFSET + (((cksum) >> 12) & 0x3f))
+#define TRLR_SET_CSUM2(cksum) (TRLR_OFFSET + (((cksum) >>  6) & 0x3f))
+#define TRLR_SET_CSUM3(cksum) (TRLR_OFFSET + (((cksum)      ) & 0x3f))
+
+/* Check that a trailer byte is reasonable.  */
+#define TRLR_CHECK(ch) (((ch) & TRLR_OFFSET) == TRLR_OFFSET)
+
+/* Get data from the trailer.  This evaluates its argument multiple
+   times.  */
+#define TRLR_GET_CKSUM(trlr) \
+  ((((trlr)[TRLR_INDX_CSUM1] & 0x3f) << 12) \
+   + (((trlr)[TRLR_INDX_CSUM2] & 0x3f) <<  6) \
+   + ((trlr)[TRLR_INDX_CSUM3] & 0x3f))
+
+/* The sequence number modulos.  */
+#define SEQ_MODULOS (64)
+
+/* Set to 1 if the target is open.  */
+static int mips_is_open;
+
+/* The next sequence number to send.  */
+static int mips_send_seq;
+
+/* The next sequence number we expect to receive.  */
+static int mips_receive_seq;
+
+/* The time to wait before retransmitting a packet, in seconds.  */
+static int mips_retransmit_wait = 3;
+
+/* The number of times to try retransmitting a packet before giving up.  */
+static int mips_send_retries = 10;
+
+/* The number of garbage characters to accept when looking for an
+   SYN for the next packet.  */
+static int mips_syn_garbage = 1050;
+
+/* The time to wait for a packet, in seconds.  */
+static int mips_receive_wait = 30;
+
+/* Set if we have sent a packet to the board but have not yet received
+   a reply.  */
+static int mips_need_reply = 0;
+
+/* This can be set to get debugging with ``set remotedebug''.  */
+static int mips_debug = 0;
+
+/* Read a character from the remote, aborting on error.  Returns -2 on
+   timeout (since that's what serial_readchar returns).  */
+
+static int
+mips_readchar (timeout)
+     int timeout;
+{
+  int ch;
+
+  ch = serial_readchar (timeout);
+  if (ch == EOF)
+    error ("End of file from remote");
+  if (ch == -3)
+    error ("Error reading from remote: %s", safe_strerror (errno));
+  if (mips_debug > 1)
+    {
+      if (ch != -2)
+	printf_filtered ("Read '%c' %d 0x%x\n", ch, ch, ch);
+      else
+	printf_filtered ("Timed out in read\n");
+    }
+  return ch;
+}
+
+/* Get a packet header, putting the data in the supplied buffer.
+   PGARBAGE is a pointer to the number of garbage characters received
+   so far.  CH is the last character received.  Returns 0 for success,
+   or -1 for timeout.  */
+
+static int
+mips_receive_header (hdr, pgarbage, ch, timeout)
+     unsigned char *hdr;
+     int *pgarbage;
+     int ch;
+     int timeout;
+{
+  int i;
+
+  while (1)
+    {
+      /* Wait for a SYN.  mips_syn_garbage is intended to prevent
+	 sitting here indefinitely if the board sends us one garbage
+	 character per second.  ch may already have a value from the
+	 last time through the loop.  */
+      while (ch != SYN)
+	{
+	  ch = mips_readchar (timeout);
+	  if (ch == -2)
+	    return -1;
+	  if (ch != SYN)
+	    {
+	      /* Printing the character here lets the user of gdb see
+		 what the program is outputting, if the debugging is
+		 being done on the console port.  FIXME: Perhaps this
+		 should be filtered?  */
+	      putchar (ch);
+
+	      ++*pgarbage;
+	      if (*pgarbage > mips_syn_garbage)
+		error ("Remote debugging protocol failure");
+	    }
+	}
+
+      /* Get the packet header following the SYN.  */
+      for (i = 1; i < HDR_LENGTH; i++)
+	{
+	  ch = mips_readchar (timeout);
+	  if (ch == -2)
+	    return -1;
+
+	  /* Make sure this is a header byte.  */
+	  if (ch == SYN || ! HDR_CHECK (ch))
+	    break;
+
+	  hdr[i] = ch;
+	}
+
+      /* If we got the complete header, we can return.  Otherwise we
+	 loop around and keep looking for SYN.  */
+      if (i >= HDR_LENGTH)
+	return 0;
+    }
+}
+
+/* Get a packet header, putting the data in the supplied buffer.
+   PGARBAGE is a pointer to the number of garbage characters received
+   so far.  The last character read is returned in *PCH.  Returns 0
+   for success, -1 for timeout, -2 for error.  */
+
+static int
+mips_receive_trailer (trlr, pgarbage, pch, timeout)
+     unsigned char *trlr;
+     int *pgarbage;
+     int *pch;
+     int timeout;
+{
+  int i;
+  int ch;
+
+  for (i = 0; i < TRLR_LENGTH; i++)
+    {
+      ch = mips_readchar (timeout);
+      *pch = ch;
+      if (ch == -2)
+	return -1;
+      if (! TRLR_CHECK (ch))
+	return -2;
+      trlr[i] = ch;
+    }
+  return 0;
+}
+
+/* Get the checksum of a packet.  HDR points to the packet header.
+   DATA points to the packet data.  LEN is the length of DATA.  */
+
+static int
+mips_cksum (hdr, data, len)
+     const unsigned char *hdr;
+     const unsigned char *data;
+     int len;
+{
+  register const unsigned char *p;
+  register int c;
+  register int cksum;
+
+  cksum = 0;
+
+  /* The initial SYN is not included in the checksum.  */
+  c = HDR_LENGTH - 1;
+  p = hdr + 1;
+  while (c-- != 0)
+    cksum += *p++;
+  
+  c = len;
+  p = data;
+  while (c-- != 0)
+    cksum += *p++;
+
+  return cksum;
+}
+
+/* Send a packet containing the given ASCII string.  */
+
+static void
+mips_send_packet (s)
+     const char *s;
+{
+  unsigned int len;
+  unsigned char *packet;
+  register int cksum;
+  int try;
+
+  len = strlen (s);
+  if (len > DATA_MAXLEN)
+    error ("MIPS protocol data packet too long: %s", s);
+
+  packet = (unsigned char *) alloca (HDR_LENGTH + len + TRLR_LENGTH + 1);
+
+  packet[HDR_INDX_SYN] = HDR_SET_SYN (1, len, mips_send_seq);
+  packet[HDR_INDX_TYPE_LEN] = HDR_SET_TYPE_LEN (1, len, mips_send_seq);
+  packet[HDR_INDX_LEN1] = HDR_SET_LEN1 (1, len, mips_send_seq);
+  packet[HDR_INDX_SEQ] = HDR_SET_SEQ (1, len, mips_send_seq);
+
+  memcpy (packet + HDR_LENGTH, s, len);
+
+  cksum = mips_cksum (packet, packet + HDR_LENGTH, len);
+  packet[HDR_LENGTH + len + TRLR_INDX_CSUM1] = TRLR_SET_CSUM1 (cksum);
+  packet[HDR_LENGTH + len + TRLR_INDX_CSUM2] = TRLR_SET_CSUM2 (cksum);
+  packet[HDR_LENGTH + len + TRLR_INDX_CSUM3] = TRLR_SET_CSUM3 (cksum);
+
+  /* Increment the sequence number.  This will set mips_send_seq to
+     the sequence number we expect in the acknowledgement.  */
+  mips_send_seq = (mips_send_seq + 1) % SEQ_MODULOS;
+
+  /* We can only have one outstanding data packet, so we just wait for
+     the acknowledgement here.  Keep retransmitting the packet until
+     we get one, or until we've tried too many times.  */
+  for (try = 0; try < mips_send_retries; try++)
+    {
+      int garbage;
+      int ch;
+
+      if (mips_debug > 0)
+	{
+	  packet[HDR_LENGTH + len + TRLR_LENGTH] = '\0';
+	  printf_filtered ("Writing \"%s\"\n", packet + 1);
+	}
+
+      if (serial_write (packet, HDR_LENGTH + len + TRLR_LENGTH) == 0)
+	error ("write to target failed: %s", safe_strerror (errno));
+
+      garbage = 0;
+      ch = 0;
+      while (1)
+	{
+	  unsigned char hdr[HDR_LENGTH + 1];
+	  unsigned char trlr[TRLR_LENGTH + 1];
+	  int err;
+	  int seq;
+
+	  /* Get the packet header.  If we time out, resend the data
+	     packet.  */
+	  err = mips_receive_header (hdr, &garbage, ch, mips_retransmit_wait);
+	  if (err != 0)
+	    break;
+
+	  ch = 0;
+
+	  /* If we get a data packet, assume it is a duplicate and
+	     ignore it.  FIXME: If the acknowledgement is lost, this
+	     data packet may be the packet the remote sends after the
+	     acknowledgement.  */
+	  if (HDR_IS_DATA (hdr))
+	    continue;
+
+	  /* If the length is not 0, this is a garbled packet.  */
+	  if (HDR_GET_LEN (hdr) != 0)
+	    continue;
+
+	  /* Get the packet trailer.  */
+	  err = mips_receive_trailer (trlr, &garbage, &ch,
+				      mips_retransmit_wait);
+
+	  /* If we timed out, resend the data packet.  */
+	  if (err == -1)
+	    break;
+
+	  /* If we got a bad character, reread the header.  */
+	  if (err != 0)
+	    continue;
+
+	  /* If the checksum does not match the trailer checksum, this
+	     is a bad packet; ignore it.  */
+	  if (mips_cksum (hdr, (unsigned char *) NULL, 0)
+	      != TRLR_GET_CKSUM (trlr))
+	    continue;
+
+	  if (mips_debug > 0)
+	    {
+	      hdr[HDR_LENGTH] = '\0';
+	      trlr[TRLR_LENGTH] = '\0';
+	      printf_filtered ("Got ack %d \"%s%s\"\n",
+			       HDR_GET_SEQ (hdr), hdr, trlr);
+	    }
+
+	  /* If this ack is for the current packet, we're done.  */
+	  seq = HDR_GET_SEQ (hdr);
+	  if (seq == mips_send_seq)
+	    return;
+
+	  /* If this ack is for the last packet, resend the current
+	     packet.  */
+	  if ((seq + 1) % SEQ_MODULOS == mips_send_seq)
+	    break;
+
+	  /* Otherwise this is a bad ack; ignore it.  Increment the
+	     garbage count to ensure that we do not stay in this loop
+	     forever.  */
+	  ++garbage;
+	}
+    }
+
+  error ("Remote did not acknowledge packet");
+}
+
+/* Receive and acknowledge a packet, returning the data in BUFF (which
+   should be DATA_MAXLEN + 1 bytes).  The protocol documentation
+   implies that only the sender retransmits packets, so this code just
+   waits silently for a packet.  It returns the length of the received
+   packet.  */
+
+static int
+mips_receive_packet (buff)
+     char *buff;
+{
+  int ch;
+  int garbage;
+  int len;
+  unsigned char ack[HDR_LENGTH + TRLR_LENGTH + 1];
+  int cksum;
+
+  ch = 0;
+  garbage = 0;
+  while (1)
+    {
+      unsigned char hdr[HDR_LENGTH];
+      unsigned char trlr[TRLR_LENGTH];
+      int i;
+      int err;
+
+      if (mips_receive_header (hdr, &garbage, ch, mips_receive_wait) != 0)
+	error ("Timed out waiting for remote packet");
+
+      ch = 0;
+
+      /* An acknowledgement is probably a duplicate; ignore it.  */
+      if (! HDR_IS_DATA (hdr))
+	{
+	  if (mips_debug > 0)
+	    printf_filtered ("Ignoring unexpected ACK\n");
+	  continue;
+	}
+
+      /* If this is the wrong sequence number, ignore it.  */
+      if (HDR_GET_SEQ (hdr) != mips_receive_seq)
+	{
+	  if (mips_debug > 0)
+	    printf_filtered ("Ignoring sequence number %d (want %d)\n",
+			     HDR_GET_SEQ (hdr), mips_receive_seq);
+	  continue;
+	}
+
+      len = HDR_GET_LEN (hdr);
+
+      for (i = 0; i < len; i++)
+	{
+	  int rch;
+
+	  rch = mips_readchar (mips_receive_wait);
+	  if (rch == SYN)
+	    {
+	      ch = SYN;
+	      break;
+	    }
+	  if (rch == -2)
+	    error ("Timed out waiting for remote packet");
+	  buff[i] = rch;
+	}
+
+      if (i < len)
+	{
+	  if (mips_debug > 0)
+	    printf_filtered ("Got new SYN after %d chars (wanted %d)\n",
+			     i, len);
+	  continue;
+	}
+
+      err = mips_receive_trailer (trlr, &garbage, &ch, mips_receive_wait);
+      if (err == -1)
+	error ("Timed out waiting for packet");
+      if (err == -2)
+	{
+	  if (mips_debug > 0)
+	    printf_filtered ("Got SYN when wanted trailer\n");
+	  continue;
+	}
+
+      if (mips_cksum (hdr, buff, len) == TRLR_GET_CKSUM (trlr))
+	break;
+
+      if (mips_debug > 0)
+	printf_filtered ("Bad checksum; data %d, trailer %d\n",
+			 mips_cksum (hdr, buff, len),
+			 TRLR_GET_CKSUM (trlr));
+
+      /* The checksum failed.  Send an acknowledgement for the
+	 previous packet to tell the remote to resend the packet.  */
+      ack[HDR_INDX_SYN] = HDR_SET_SYN (0, 0, mips_receive_seq);
+      ack[HDR_INDX_TYPE_LEN] = HDR_SET_TYPE_LEN (0, 0, mips_receive_seq);
+      ack[HDR_INDX_LEN1] = HDR_SET_LEN1 (0, 0, mips_receive_seq);
+      ack[HDR_INDX_SEQ] = HDR_SET_SEQ (0, 0, mips_receive_seq);
+
+      cksum = mips_cksum (ack, (unsigned char *) NULL, 0);
+
+      ack[HDR_LENGTH + TRLR_INDX_CSUM1] = TRLR_SET_CSUM1 (cksum);
+      ack[HDR_LENGTH + TRLR_INDX_CSUM2] = TRLR_SET_CSUM2 (cksum);
+      ack[HDR_LENGTH + TRLR_INDX_CSUM3] = TRLR_SET_CSUM3 (cksum);
+
+      if (mips_debug > 0)
+	{
+	  ack[HDR_LENGTH + TRLR_LENGTH] = '\0';
+	  printf_filtered ("Writing ack %d \"%s\"\n", mips_receive_seq,
+			   ack + 1);
+	}
+
+      if (serial_write (ack, HDR_LENGTH + TRLR_LENGTH) == 0)
+	error ("write to target failed: %s", safe_strerror (errno));
+    }
+
+  if (mips_debug > 0)
+    {
+      buff[len] = '\0';
+      printf_filtered ("Got packet \"%s\"\n", buff);
+    }
+
+  /* We got the packet.  Send an acknowledgement.  */
+  mips_receive_seq = (mips_receive_seq + 1) % SEQ_MODULOS;
+
+  ack[HDR_INDX_SYN] = HDR_SET_SYN (0, 0, mips_receive_seq);
+  ack[HDR_INDX_TYPE_LEN] = HDR_SET_TYPE_LEN (0, 0, mips_receive_seq);
+  ack[HDR_INDX_LEN1] = HDR_SET_LEN1 (0, 0, mips_receive_seq);
+  ack[HDR_INDX_SEQ] = HDR_SET_SEQ (0, 0, mips_receive_seq);
+
+  cksum = mips_cksum (ack, (unsigned char *) NULL, 0);
+
+  ack[HDR_LENGTH + TRLR_INDX_CSUM1] = TRLR_SET_CSUM1 (cksum);
+  ack[HDR_LENGTH + TRLR_INDX_CSUM2] = TRLR_SET_CSUM2 (cksum);
+  ack[HDR_LENGTH + TRLR_INDX_CSUM3] = TRLR_SET_CSUM3 (cksum);
+
+  if (mips_debug > 0)
+    {
+      ack[HDR_LENGTH + TRLR_LENGTH] = '\0';
+      printf_filtered ("Writing ack %d \"%s\"\n", mips_receive_seq,
+		       ack + 1);
+    }
+
+  if (serial_write (ack, HDR_LENGTH + TRLR_LENGTH) == 0)
+    error ("write to target failed: %s", safe_strerror (errno));
+
+  return len;
+}
+
+/* Optionally send a request to the remote system and optionally wait
+   for the reply.  This implements the remote debugging protocol,
+   which is built on top of the packet protocol defined above.  Each
+   request has an ADDR argument and a DATA argument.  The following
+   requests are defined:
+
+   \0	don't send a request; just wait for a reply
+   i	read word from instruction space at ADDR
+   d	read word from data space at ADDR
+   I	write DATA to instruction space at ADDR
+   D	write DATA to data space at ADDR
+   r	read register number ADDR
+   R	set register number ADDR to value DATA
+   c	continue execution (if ADDR != 1, set pc to ADDR)
+   s	single step (if ADDR != 1, set pc to ADDR)
+
+   The read requests return the value requested.  The write requests
+   return the previous value in the changed location.  The execution
+   requests return a UNIX wait value (the approximate signal which
+   caused execution to stop is in the upper eight bits).
+
+   If PERR is not NULL, this function waits for a reply.  If an error
+   occurs, it sets *PERR to 1 and sets errno according to what the
+   target board reports.  */
+
+static int
+mips_request (cmd, addr, data, perr)
+     char cmd;
+     unsigned int addr;
+     unsigned int data;
+     int *perr;
+{
+  char buff[DATA_MAXLEN + 1];
+  int len;
+  int rpid;
+  char rcmd;
+  int rerrflg;
+  int rresponse;
+  
+  if (cmd != '\0')
+    {
+      if (mips_need_reply)
+	fatal ("mips_request: Trying to send command before reply");
+      sprintf (buff, "0x0 %c 0x%x 0x%x", cmd, addr, data);
+      mips_send_packet (buff);
+      mips_need_reply = 1;
+    }
+
+  if (perr == (int *) NULL)
+    return 0;
+
+  if (! mips_need_reply)
+    fatal ("mips_request: Trying to get reply before command");
+
+  mips_need_reply = 0;
+
+  len = mips_receive_packet (buff);
+  buff[len] = '\0';
+
+  if (sscanf (buff, "0x%x %c 0x%x 0x%x",
+	      &rpid, &rcmd, &rerrflg, &rresponse) != 4
+      || rpid != 0
+      || (cmd != '\0' && rcmd != cmd))
+    error ("Bad response from remote board");
+
+  if (rerrflg != 0)
+    {
+      *perr = 1;
+
+      /* FIXME: This will returns MIPS errno numbers, which may or may
+	 not be the same as errno values used on other systems.  If
+	 they stick to common errno values, they will be the same, but
+	 if they don't, they must be translated.  */
+      errno = rresponse;
+
+      return 0;
+    }
+
+  *perr = 0;
+  return rresponse;
+}
+
+/* Open a connection to the remote board.  */
+
+static void
+mips_open (name, from_tty)
+     char *name;
+     int from_tty;
+{
+  int err;
+  char cr;
+  char buff[DATA_MAXLEN + 1];
+
+  if (name == 0)
+    error (
+"To open a MIPS remote debugging connection, you need to specify what serial\n\
+device is attached to the target board (e.g., /dev/ttya).");
+
+  target_preopen (from_tty);
+
+  if (mips_is_open)
+    mips_close (0);
+
+  if (serial_open (name) == 0)
+    perror_with_name (name);
+
+  mips_is_open = 1;
+
+  /* The board seems to want to send us a packet.  I don't know what
+     it means.  */
+  cr = '\r';
+  serial_write (&cr, 1);
+  mips_receive_packet (buff);
+
+  /* If this doesn't call error, we have connected; we don't care if
+     the request itself succeeds or fails.  */
+  mips_request ('r', (unsigned int) 0, (unsigned int) 0, &err);
+
+  if (from_tty)
+    printf ("Remote MIPS debugging using %s\n", name);
+  push_target (&mips_ops);	/* Switch to using remote target now */
+
+  start_remote ();		/* Initialize gdb process mechanisms */
+}
+
+/* Close a connection to the remote board.  */
+
+static void
+mips_close (quitting)
+     int quitting;
+{
+  if (mips_is_open)
+    {
+      /* Get the board out of remote debugging mode.  */
+      mips_request ('x', (unsigned int) 0, (unsigned int) 0,
+		    (int *) NULL);
+      serial_close ();
+      mips_is_open = 0;
+    }
+}
+
+/* Detach from the remote board.  */
+
+static void
+mips_detach (args, from_tty)
+     char *args;
+     int from_tty;
+{
+  if (args)
+    error ("Argument given to \"detach\" when remotely debugging.");
+
+  pop_target ();
+  if (from_tty)
+    printf ("Ending remote MIPS debugging.\n");
+}
+
+/* Tell the target board to resume.  This does not wait for a reply
+   from the board.  */
+
+static void
+mips_resume (step, siggnal)
+     int step, siggnal;
+{
+  if (siggnal)
+    error ("Can't send signals to a remote system.  Try `handle %d ignore'.",
+	   siggnal);
+
+  mips_request (step ? 's' : 'c',
+		(unsigned int) read_register (PC_REGNUM),
+		(unsigned int) 0,
+		(int *) NULL);
+}
+
+/* Wait until the remote stops, and return a wait status.  */
+
+static int
+mips_wait (status)
+     WAITTYPE *status;
+{
+  int rstatus;
+  int err;
+
+  /* If we have not sent a single step or continue command, then the
+     board is waiting for us to do something.  Return a status
+     indicating that it is stopped.  */
+  if (! mips_need_reply)
+    {
+      WSETSTOP (*status, SIGTRAP);
+      return 0;
+    }
+
+  rstatus = mips_request ('\0', (unsigned int) 0, (unsigned int) 0, &err);
+  if (err)
+    error ("Remote failure: %s", safe_strerror (errno));
+
+  /* FIXME: The target board uses numeric signal values which are
+     those used on MIPS systems.  If the host uses different signal
+     values, we need to translate here.  I believe all Unix systems
+     use the same values for the signals the board can return, which
+     are: SIGINT, SIGSEGV, SIGBUS, SIGILL, SIGFPE, SIGTRAP.  */
+
+  /* FIXME: The target board uses a standard Unix wait status int.  If
+     the host system does not, we must translate here.  */
+
+  *status = rstatus;
+
+  return 0;
+}
+
+/* We have to map between the register numbers used by gdb and the
+   register numbers used by the debugging protocol.  This function
+   assumes that we are using tm-mips.h.  */
+
+#define REGNO_OFFSET 96
+
+static int
+mips_map_regno (regno)
+     int regno;
+{
+  if (regno < 32)
+    return regno;
+  if (regno >= FP0_REGNUM && regno < FP0_REGNUM + 32)
+    return regno - FP0_REGNUM + 32;
+  switch (regno)
+    {
+    case PC_REGNUM:
+      return REGNO_OFFSET + 0;
+    case CAUSE_REGNUM:
+      return REGNO_OFFSET + 1;
+    case HI_REGNUM:
+      return REGNO_OFFSET + 2;
+    case LO_REGNUM:
+      return REGNO_OFFSET + 3;
+    case FCRCS_REGNUM:
+      return REGNO_OFFSET + 4;
+    case FCRIR_REGNUM:
+      return REGNO_OFFSET + 5;
+    default:
+      /* FIXME: Is there a way to get the status register?  */
+      return 0;
+    }
+}
+
+/* Fetch the remote registers.  */
+
+static void
+mips_fetch_registers (regno)
+     int regno;
+{
+  REGISTER_TYPE val;
+  int err;
+
+  if (regno == -1)
+    {
+      for (regno = 0; regno < NUM_REGS; regno++)
+	mips_fetch_registers (regno);
+      return;
+    }
+
+  val = mips_request ('r', (unsigned int) mips_map_regno (regno),
+		      (unsigned int) 0, &err);
+  if (err)
+    error ("Can't read register %d: %s", regno, safe_strerror (errno));
+
+  /* We got the number the register holds, but gdb expects to see a
+     value in the target byte ordering.  */
+  SWAP_TARGET_AND_HOST (val, sizeof (REGISTER_TYPE));
+  supply_register (regno, (char *) &val);
+}
+
+/* Prepare to store registers.  The MIPS protocol can store individual
+   registers, so this function doesn't have to do anything.  */
+
+static void
+mips_prepare_to_store ()
+{
+}
+
+/* Store remote register(s).  */
+
+static void
+mips_store_registers (regno)
+     int regno;
+{
+  int err;
+
+  if (regno == -1)
+    {
+      for (regno = 0; regno < NUM_REGS; regno++)
+	mips_store_registers (regno);
+      return;
+    }
+
+  mips_request ('R', (unsigned int) mips_map_regno (regno),
+		(unsigned int) read_register (regno),
+		&err);
+  if (err)
+    error ("Can't write register %d: %s", regno, safe_strerror (errno));
+}
+
+/* Fetch a word from the target board.  */
+
+static int 
+mips_fetch_word (addr)
+     CORE_ADDR addr;
+{
+  int val;
+  int err;
+
+  val = mips_request ('d', (unsigned int) addr, (unsigned int) 0, &err);
+  if (err)
+    {
+      /* Data space failed; try instruction space.  */
+      val = mips_request ('i', (unsigned int) addr, (unsigned int) 0, &err);
+      if (err)
+	error ("Can't read address 0x%x: %s", addr, safe_strerror (errno));
+    }
+  return val;
+}
+
+/* Store a word to the target board.  */
+
+static void
+mips_store_word (addr, val)
+     CORE_ADDR addr;
+     int val;
+{
+  int err;
+
+  mips_request ('D', (unsigned int) addr, (unsigned int) val, &err);
+  if (err)
+    {
+      /* Data space failed; try instruction space.  */
+      mips_request ('I', (unsigned int) addr, (unsigned int) val, &err);
+      if (err)
+	error ("Can't write address 0x%x: %s", addr, safe_strerror (errno));
+    }
+}
+
+/* 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.  Note that protocol gives us the correct value
+   for a longword, since it transfers values in ASCII.  We want the
+   byte values, so we have to swap the longword values.  */
+
+static int
+mips_xfer_memory (memaddr, myaddr, len, write, ignore)
+     CORE_ADDR memaddr;
+     char *myaddr;
+     int len;
+     int write;
+     struct target_ops *ignore;
+{
+  register int i;
+  /* Round starting address down to longword boundary.  */
+  register CORE_ADDR addr = memaddr &~ 3;
+  /* Round ending address up; get number of longwords that makes.  */
+  register int count = (((memaddr + len) - addr) + 3) / 4;
+  /* Allocate buffer of that many longwords.  */
+  register unsigned int *buffer = (unsigned int *) alloca (count * 4);
+
+  if (write)
+    {
+      /* Fill start and end extra bytes of buffer with existing data.  */
+      if (addr != memaddr || len < 4)
+	{
+	  /* Need part of initial word -- fetch it.  */
+	  buffer[0] = mips_fetch_word (addr);
+	  SWAP_TARGET_AND_HOST (buffer, 4);
+	}
+
+      if (count > 1)		/* FIXME, avoid if even boundary */
+	{
+	  buffer[count - 1] = mips_fetch_word (addr + (count - 1) * 4);
+	  SWAP_TARGET_AND_HOST (buffer + (count - 1) * 4, 4);
+	}
+
+      /* Copy data to be written over corresponding part of buffer */
+
+      memcpy ((char *) buffer + (memaddr & 3), myaddr, len);
+
+      /* Write the entire buffer.  */
+
+      for (i = 0; i < count; i++, addr += 4)
+	{
+	  SWAP_TARGET_AND_HOST (buffer + i, 4);
+	  mips_store_word (addr, buffer[i]);
+	}
+    }
+  else
+    {
+      /* Read all the longwords */
+      for (i = 0; i < count; i++, addr += 4)
+	{
+	  buffer[i] = mips_fetch_word (addr);
+	  SWAP_TARGET_AND_HOST (buffer + i, 4);
+	  QUIT;
+	}
+
+      /* Copy appropriate bytes out of the buffer.  */
+      memcpy (myaddr, (char *) buffer + (memaddr & (sizeof (int) - 1)), len);
+    }
+  return len;
+}
+
+/* Print info on this target.  */
+
+static void
+mips_files_info (ignore)
+     struct target_ops *ignore;
+{
+  printf ("Debugging a MIPS board over a serial line.\n");
+}
+
+/* Load an executable onto the board.  */
+
+static void
+mips_load (args, from_tty)
+     char *args;
+     int from_tty;
+{
+  bfd *abfd;
+  asection *s;
+  int err;
+
+  abfd = bfd_openr (args, 0);
+  if (abfd == (bfd *) NULL)
+    error ("Unable to open file %s", args);
+
+  if (bfd_check_format (abfd, bfd_object) == 0)
+    error ("%s: Not an object file", args);
+
+  for (s = abfd->sections; s != (asection *) NULL; s = s->next)
+    {
+      if ((s->flags & SEC_LOAD) != 0)
+	{
+	  bfd_size_type size;
+
+	  size = bfd_get_section_size_before_reloc (s);
+	  if (size > 0)
+	    {
+	      char *buffer;
+	      struct cleanup *old_chain;
+	      bfd_vma vma;
+
+	      buffer = xmalloc (size);
+	      old_chain = make_cleanup (free, buffer);
+
+	      vma = bfd_get_section_vma (abfd, s);
+	      printf_filtered ("Loading section %s, size 0x%x vma 0x%x\n",
+			       bfd_get_section_name (abfd, s), size, vma);
+	      bfd_get_section_contents (abfd, s, buffer, 0, size);
+	      mips_xfer_memory (vma, buffer, size, 1, &mips_ops);
+
+	      do_cleanups (old_chain);
+	    }
+	}
+    }
+
+  mips_request ('R', (unsigned int) mips_map_regno (PC_REGNUM),
+		(unsigned int) abfd->start_address,
+		&err);
+  if (err)
+    error ("Can't write PC register: %s", safe_strerror (errno));
+
+  bfd_close (abfd);
+
+  /* FIXME: Should we call symbol_file_add here?  */
+}
+
+/* Start running on the target board.  */
+
+static void
+mips_create_inferior (execfile, args, env)
+     char *execfile;
+     char *args;
+     char **env;
+{
+  CORE_ADDR entry_pt;
+
+  /* FIXME: Actually, we probably could pass arguments.  */
+  if (args && *args)
+    error ("Can't pass arguments to remote MIPS board.");
+
+  if (execfile == 0 || exec_bfd == 0)
+    error ("No exec file specified");
+
+  entry_pt = (CORE_ADDR) bfd_get_start_address (exec_bfd);
+
+  init_wait_for_inferior ();
+
+  proceed (entry_pt, -1, 0);
+}
+
+/* Clean up after a process.  Actually nothing to do.  */
+
+static void
+mips_mourn_inferior ()
+{
+  generic_mourn_inferior ();
+}
+
+/* The target vector.  */
+
+struct target_ops mips_ops =
+{
+  "mips",			/* to_shortname */
+  "Remote MIPS debugging over serial line",	/* to_longname */
+  "Debug a board using the MIPS remote debugging protocol over a serial line.\n\
+Specify the serial device it is connected to (e.g., /dev/ttya).",  /* to_doc */
+  mips_open,			/* to_open */
+  mips_close,			/* to_close */
+  NULL,				/* to_attach */
+  mips_detach,			/* to_detach */
+  mips_resume,			/* to_resume */
+  mips_wait,			/* to_wait */
+  mips_fetch_registers,		/* to_fetch_registers */
+  mips_store_registers,		/* to_store_registers */
+  mips_prepare_to_store,	/* to_prepare_to_store */
+  mips_xfer_memory,		/* to_xfer_memory */
+  mips_files_info,		/* to_files_info */
+  NULL,				/* to_insert_breakpoint */
+  NULL,				/* 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 */
+  NULL,				/* to_kill */
+  mips_load,			/* to_load */
+  NULL,				/* to_lookup_symbol */
+  mips_create_inferior,		/* to_create_inferior */
+  mips_mourn_inferior,		/* to_mourn_inferior */
+  NULL,				/* to_can_run */
+  NULL,				/* 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_mips ()
+{
+  add_target (&mips_ops);
+
+  add_show_from_set (
+    add_set_cmd ("remotedebug", no_class, var_zinteger, (char *) &mips_debug,
+		   "Set debugging of remote MIPS serial I/O.\n\
+When non-zero, each packet sent or received with the remote target\n\
+is displayed.  Higher numbers produce more debugging.", &setlist),
+	&showlist);
+}