Debugging PowerPC 860 embedded target with Abatron BDI 2000: Remote packet too long errors.

[Cristian Alonso <CALONSO at teldat dot es>]

Hi,
I am using an Abatron (Swiss company that makes BDM's which work whith gdb)
BDI2000 to debug an embedded target with a PowerPC 860 CPU using Insight-5.1
(last prerelease snapshot available). 

After compiing last Insight-5.1 prerelease available and connecting to the
remote target i get lots of the following errors:
(gdb) target remote 172.24.78.42:2001
Remote debugging using 172.24.78.42:2001
Remote packet too long: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Ignoring packet error, continuing...

After taking a look at GDB's source files, i found function
build_remote_packet_sizes in remote.c, in which 
the following lines are executed:
.
.
.
  remote_packet_size = 400 - 1;
  /* Should REGISTER_BYTES needs more space than the default, adjust
     the size accordingly. Remember that each byte is encoded as two
     characters. 32 is the overhead for the packet header /
     footer. NOTE: cagney/1999-10-26: I suspect that 8
     (``$NN:G...#NN'') is a better guess, the below has been padded a
     little. */
  if (REGISTER_BYTES > ((remote_packet_size - 32) / 2))
    remote_packet_size = (REGISTER_BYTES * 2 + 32);
.
.

Changing the value of remote_packet_size to 5 Kbytes works fine with my
BDI2000. It makes my insight work fine and allows me to laugh at all the
Windriver Visionclick users who told me i would not be able to debug using
"that free software of yours" ;-).

It seems that i should be able to find the definition of REGISTER_BYTES and
change it to a different value and submit the patch but i have the following
problems:
  - I have not been able to find in which file exactly (ppc.h does not seem
to work...)do i have to change the definition of REGISTER_BYTES.
  - I do not know which value is correct for this #define (it seems that it
has to be higher, and it has something to do with how many registers do i
have in my arch, but how do i find out?)

Thanks in advance,
Cristian Alonso Aldama
Development Group Manager
R&D Department
e-mail: calonso@teldat.es 
http://www.teldat.es