21.3.5 MIPS Embedded

gdb can use the MIPS remote debugging protocol to talk to a MIPS board attached to a serial line. This is available when you configure gdb with ‘--target=mips-elf’.

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

target mips port

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

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

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

target mips hostname:portnumber

On some gdb host configurations, you can specify a TCP connection (for instance, to a serial line managed by a terminal concentrator) instead of a serial port, using the syntax ‘hostname:portnumber’.

target pmon port

PMON ROM monitor.

target ddb port

NEC's DDB variant of PMON for Vr4300.

target lsi port

LSI variant of PMON.

target r3900 dev

Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.

target array dev

Array Tech LSI33K RAID controller board.

gdb also supports these special commands for MIPS targets:

set mipsfpu double

set mipsfpu single

set mipsfpu none

set mipsfpu auto

show mipsfpu

If your target board does not support the MIPS floating point coprocessor, you should use the command ‘set mipsfpu none’ (if you need this, you may wish to put the command in your gdb init file). This tells gdb how to find the return value of functions which return floating point values. It also allows gdb to avoid saving the floating point registers when calling functions on the board. If you are using a floating point coprocessor with only single precision floating point support, as on the r4650 processor, use the command ‘set mipsfpu single’. The default double precision floating point coprocessor may be selected using ‘set mipsfpu double’.

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

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

set timeout seconds

set retransmit-timeout seconds

show timeout

show retransmit-timeout

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

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

set syn-garbage-limit num

Limit the maximum number of characters gdb should ignore when it tries to synchronize with the remote target. The default is 10 characters. Setting the limit to -1 means there's no limit.

show syn-garbage-limit

Show the current limit on the number of characters to ignore when trying to synchronize with the remote system.

set monitor-prompt prompt

Tell gdb to expect the specified prompt string from the remote monitor. The default depends on the target:

pmon target

‘PMON’

ddb target

‘NEC010’

lsi target

‘PMON>’

show monitor-prompt

Show the current strings gdb expects as the prompt from the remote monitor.

set monitor-warnings

Enable or disable monitor warnings about hardware breakpoints. This has effect only for the lsi target. When on, gdb will display warning messages whose codes are returned by the lsi PMON monitor for breakpoint commands.

show monitor-warnings

Show the current setting of printing monitor warnings.

pmon command

This command allows sending an arbitrary command string to the monitor. The monitor must be in debug mode for this to work.