pyocd: startup hangs if target firmware is compiled for one core and debugged with pyocd

[rgrr]

complicated...

For target firmware:

• #define configNUMBER_OF_CORES 1
• debug with pyocd
• pyocd hangs in timer_busy_wait_until()
• actually called from usb_thread(), cdc_uart_init()
• seems that TIMER0 (0x400b0000) is not running

Don't know yet if this is a problem in pyocd or in the startup sequence.

PS: target firmware is actually the probe firmware running on an RP2350

Opened issue: FreeRTOS/FreeRTOS-Kernel#1374
Existing issue: raspberrypi/pico-sdk#1152

[rgrr]

timer->DBGPAUSE equals 7.

I guess that pyocd keeps the second core in HALT, so DBGPAUSE stops the timer.

OpenOCD does not have the problem because it starts both cores.

[rgrr]

#if configNUMBER_OF_CORES != 2
    // this is actually just for debugging the probe firmware running with just one core (good for pyocd)
    // allow to run TIMER0 even in debug pause which would otherwise be inhibited because TIMER0.DBGPAUSE=7
    multicore_reset_core1();
#endif

on startup solves this. Not sure if there are implications. And not sure if this shouldn't be fixed either in FreeRTOS or PicoSDK.