BMDA: RP2040 does not connect via dap42 (CMSIS-DAP) adapter

[dmsc]

Trying to debug a RP2040 MCU with the dap42 debugger, via CMSIS-DAP interface, the SWD scan fails:

(gdb) tar ext :2000
Remote debugging using :2000
(gdb) mon s        
Exception: SWDP invalid ACK
SW-DP scan failed!
Failed

Problem is with target selection after a forced error, at the end of the log file:

 command: 06 00 04 00 0f 
response: 06 04 00 01 0d 00 00 00 10 00 00 00 05 00 00 00 b1 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
dap_mem_read transferred 4 blocks
ap_memread @ e00ffff0 len 16: 0d 00 00 00 10 00 00 00 05 00 00 00 b1 00 00 00
dap_swd_dp_error (protocol recovery? false)
-> dap_swj_sequence (64 cycles)
 command: 12 40 ff ff ff ff ff ff ff 0f 
response: 12 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
 command: 05 00 01 02 
response: 05 01 01 77 24 c1 0b 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
        dap_read_reg 00 0bc12477
        dap_write_reg 0c 01002927
 command: 05 00 01 0c 27 29 00 01 
response: 05 00 07 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
dap_write_reg 0c data 01002927:fault
 command: 05 00 01 06 
response: 05 00 07 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 

The code is at cmsis_dap.c, line 282:

static uint32_t dap_swd_dp_error(adiv5_debug_port_s *dp, const bool protocol_recovery)
{
	DEBUG_PROBE("dap_swd_dp_error (protocol recovery? %s)\n", protocol_recovery ? "true" : "false");
	if (dp->version >= 2 || protocol_recovery) {
		/* On protocol error target gets deselected.
		 * With DP Change, another target needs selection.
		 * => Reselect with right target! */
		dap_line_reset();
		dap_read_reg(dp, ADIV5_DP_DPIDR);
		dap_write_reg(dp, ADIV5_DP_TARGETSEL, dp->targetsel);
		/* Exception here is unexpected, so do not catch */
	}

The line with dap_write_reg(dp, ADIV5_DP_TARGETSEL, dp->targetsel); fails, as the probe returns error 7 = NO_ACK (no response from target). Note that from the reset all read and write commands fail.

Any ideas?

[dmsc]

Additional information: If I comment out the line: dap_write_reg(dp, ADIV5_DP_TARGETSEL, dp->targetsel);, the scan works, but it drops on attach:

(gdb) tar ext :2000
Remote debugging using :2000
(gdb) mon s        
Available Targets:
No. Att Driver
 1      Raspberry RP2040 M0+
 2      Raspberry RP2040 M0+
 3      Raspberry RP2040 Rescue (Attach to reset!) 
(gdb) attach 1     
Attaching to program: prog.elf, Remote target
Attaching to Remote target failed
(gdb) 

Attached new log: bad3.log

[dragonmux]

Thank you for the excellent bug report! We know what the bug is - and we forgot about this instance of the error handler when fixing the bug in the main firmware. The no-response response is actually correct, however the dap_write_reg() call for TARGETSEL must come before the DPIDR read for fun protocol reasons and then dp->fault needs resetting to 0 after the write.

This is another instance of #1359 which needs a mix of e23c781 and ba5c56c applying to this situation to correctly fix

[dragonmux]

The fix for this needs a second version of dap_write_reg(), however a partial fix is now available on branch fix/bmda-cmsis-dap-protocol-recovery. We will deal with the register write problem a bit later.

[dmsc]

Thank for your reply. I tried the fix/bmda-cmsis-dap-protocol-recovery branch over the PR #1369, now the scan works but the attach still errors out:

bad4.log

The write and the read both return error 7 (NO_ACK).

[dragonmux]

We have updated the fix branch to address the lingering issue of dap_write_reg() being used in the error recovery path and impeding the ability to complete protocol recovery. Please let us know how you get on with the branch

[dragonmux]

If this issue is not entirely solved, please let us know and we'll re-open it and work on further fixes for v1.10

[dmsc]

Hi!

Sadly, it does not work yet, this is the current log:
bad6.log

As you can see, the scan works ok, but then at attach, the commands fail.