In testing, this patch seems to fix the initial issue in #5418. However, the second hang mentioned in that issue; where a similar hang can be generated when running the script from https://learn.adafruit.com/rgb-led-matrices-matrix-panels-with-circuitpython/connecting-with-feather-rp2040-featherwing by hitting CTRL-C during startup; still exists. I captured a stack from that hang:

#0  0x1008cd78 in blast_long (data=0xbc, core=0x2000391c <displays+20>) at ../../lib/protomatter/src/core.c:814
#1  _PM_row_handler (core=0x2000391c <displays+20>) at ../../lib/protomatter/src/core.c:565
#2  0x1008cf98 in _PM_PWM_ISR () at ../../lib/protomatter/src/arch/rp2040.h:194
#3  <signal handler called>
#4  0x1008c6ee in _PM_begin (core=core@entry=0x2000391c <displays+20>) at ../../lib/protomatter/src/core.c:175
#5  0x1005b556 in common_hal_rgbmatrix_rgbmatrix_reconstruct (self=self@entry=0x20003908 <displays>,
    framebuffer=framebuffer@entry=0x0) at ../../shared-module/rgbmatrix/RGBMatrix.c:108
#6  0x10034316 in supervisor_display_move_memory () at ../../supervisor/shared/display.c:145
#7  0x10028c22 in supervisor_move_memory () at ../../supervisor/shared/memory.c:336
#8  0x10027962 in cleanup_after_vm (exception=0x4, heap=0x20006218 <allocations+20>) at ../../main.c:281
#9  run_repl () at ../../main.c:763
#10 main () at ../../main.c:853

It looks like we're still getting into the PWM interrupt handler when not configured to handle things there.

Adding the same two new lines from common_hal_rgbmatrix_timer_free() at the end of common_hal_rgbmatrix_timer_disable() seems to resolve both the "syntax error" issue as well as the "CTRL-C" scenerio.

Is this is still in process, or does it await a review?

I need to incorporate @DavePutz 's suggestion

As it'll be at least a week before I look at this again I encourage @DavePutz to PR his tested and working fix for this issue.

@DavePutz ready for your re-review.

Note that I've retargeted this PR for 7.1.x, rather than main.

Note that I've retargeted this PR for 7.1.x, rather than main.

Do you consider this a priority for 7.1.0?

not super urgent for me, it's just that this was made way before we split 7.1.x from main. I can switch it back, or we can merge it after 7.1.0 goes out.

Sounds good. Let's merge it after 7.1.0 is final, and then we can merge this and any remaining changes into main. In the meantime, it will also be in 7.1.x in case we do a 7.1.1.