GDB/OpenOCD Debugging with TinyGo on the Pico

[Jason-Duffy]

Hi there,

I'm developing a product using TinyGo on an RP2040, and I'm trying to get a decent debug setup going. The GDB session starts up just fine, however the MCU seems to lock up once I enter continue. I then have to use CTRL + C to interrupt it, and detach the MCU with CTRL+ D.

Has anyone been successful in debugging like this already? If so, can you help me out please? Terminal output below:

C:\Users\****\test-pico\blink>tinygo gdb -target=pico -programmer=cmsis-dap .
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Reading symbols from C:\Users\****\AppData\Local\Temp\tinygo1598744099\main...
Remote debugging using :3333
0x10001940 in runtime/volatile.StoreUint32 (addr=<optimized out>,
    val=<optimized out>) at C:\tinygo\src\runtime\volatile/volatile.go:37
37      func StoreUint32(addr *uint32, val uint32)
Loading section .boot2, size 0x100 lma 0x10000000
Loading section .text, size 0x1dc8 lma 0x10000100
Loading section .tinygo_stacksizes, size 0x4 lma 0x10001ec8
Loading section .data, size 0x68 lma 0x10001ecc
Start address 0x10001880, load size 7988
Transfer rate: 1 KB/sec, 1997 bytes/write.
[rp2040.core0] halted due to debug-request, current mode: Thread
xPSR: 0xf1000000 pc: 0x000000ee msp: 0x20041f00
[rp2040.core1] halted due to debug-request, current mode: Thread
xPSR: 0xf1000000 pc: 0x000000ee msp: 0x20041f00
(gdb) break main.go:16
Breakpoint 1 at 0x10001bae: file C:\Users\****\test-pico\blink/main.go, line 16.
Note: automatically using hardware breakpoints for read-only addresses.
(gdb) continue
Continuing.

Thanks,

Jason

[Jason-Duffy]

For anyone else with this issue, what was happening is the target MCU wasn't being reset after being flashed, so it hung in a weird state. Use the command monitor reset to do this, then the debug commands like continue will work as expected. I also read the openOCD manual which I found really helpful: https://openocd.org/doc/pdf/openocd.pdf and was able to write my own config files and custom shell scripts after that.