JTAG

The WPCM450 SoC has a JTAG port, which is exposed on some boards. Dell boards usually feature the 20-pin ARM JTAG.

Info : JTAG tap: wpcm450.cpu tap/device found: 0x07926f0f (mfg: 0x787 (<unknown>), part: 0x7926, ver: 0x0)

Note that the TAP reports a bogus manufacturer ID, rather than something reasonable such as Winbond.

Setting it up

• Connect your JTAG adapter to the debug port
• Start OpenOCD like this:

$ openocd -f interface/your-adapter.cfg -f target/wpcm450.cfg

• Run GDB, e.g.:

$ gdb monitor.elf --ex 'tar ext localhost:3333`
(gdb) monitor reset halt
(gdb) load
(gdb) b main
(gdb) c

A few useful OpenOCD commands

reset_config trst_and_srst combined
adapter speed 20000                  # tell OpenOCD that the adapter runs at 20 MHz
remote_bitbang use_remote_sleep on   # alternatively, tell OpenOCD not to insert any delays,
                                     # because they're handled on the adapter side (d/D commands)
soft_reset_halt                      # halt the CPU via soft reset, move PC to reset vector