How to set a watchpoint

  • version

    1.0.1

  • scope

    Example.

    This code is provided as example code for a user to base their code on.

  • description

    How to set a watchpoint

  • boards

    Unless otherwise specified, this example runs on the SliceKIT Core Board, but can easily be run on any XMOS device by using a different XN file.

Data watchpoints are used to allow XGDB to halt the execution of a the program when a condition placed on a data object by the user evaluates to true. For example, compile the following code ensuring that debug is enabled (-g):

#include <print.h>

int main() {
  int i, j = 0;
  for (i = 0; i < 5; ++i) {
    printintln(i);
  }
  return 0;
}

To set a watchpoint from xTIMEcomposer Studio

Create a new debug configuration via Run->debug Configurations->xCORE Applications. Set a breakpoint at the start of main then start debugging. Execution will now break when main is reached. In the variables view, right-click on the entry for the loop count i and choose Add Watchpoint (C/C++). In the dialog enter i == 3, then continue execution. The debugger will now break when the value of the loop index variable i evaluates to 3. This can be confirmed by hovering over the variable in the editor.

To set a watchpoint from the command line

On the command line, watchpoints are set using the watch command. For example, start XGDB, connect to the simulator and set a breakpoint on main. When run, execution will break at the start of main. You can now set a watchpoint on the variable i:

> xgdb a.xe
...etc...
(gdb) connect -s
0xffffc04e in ?? ()
(gdb) b main
Breakpoint 1 at 0x100b0: file setting_a_watchpoint.xc, line 12.
(gdb) run
...etc...
Breakpoint 1, main () at setting_a_watchpoint.xc:12
12    int i, j = 0;
(gdb) watch i == 3
Hardware watchpoint 2: i == 3
(gdb) continue
0
1
2
Hardware watchpoint 2: i == 3

Old value = 0
New value = 1
0x000100c4 in main () at setting_a_watchpoint.xc:13
13    for (i = 0; i < 5; ++i) {
(gdb) print i
$1 = 3