Debugging with GDB

Node:MIPS Embedded, Next:PA, Previous:M88K, Up:Embedded Processors

#### 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-idt-ecoff`.

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 processor` args``
`show processor`
  Use the `set processor` command to set the type of MIPS processor when you want to access processor-type-specific registers. For example, `set processor` r3041`` tells GDB to use the CPU registers appropriate for the 3041 chip. Use the `show processor` command to see what MIPS processor GDB is using. Use the `info reg` command to see what registers GDB is using.
`set mipsfpu double`
`set mipsfpu single`
`set mipsfpu none`
`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 remotedebug` n``
`show remotedebug`
  You can see some debugging information about communications with the board by setting the `remotedebug` variable. If you set it to `1` using `set remotedebug 1`, every packet is displayed. If you set it to `2`, every character is displayed. You can check the current value at any time with the command `show remotedebug`.
`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 acknowledgement 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-idt-ecoff`.)

  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.