NUCLEO-L433RC-P SWV Not Working

[jdawkins]

Hi,

I have an external PCB using STM32L432KCU6 to program and debug.  I can program this using the NUCLEO-L433RC-P (MB1319C) and NUCLEO-L476RG development boards in STLink configuration.

Using the L476, I can see the output of the SWV from printf (MCU freq is 4 MHz, matched in STM32CubeIDE software or ST-Link Utility).

If I replace the programming board for the NUCLEO-L433RC-P, I can still interact with and debug the external MCU, but the SWV output no longer works.

If I remove the Idd pin from the NUCLEO side of the board (i.e. with the inbuilt L433 chip) then the STM32CubeIDE or ST-Link utility no longer recognise any target device on the SWD bus.

In both cases, the CN2 connectors are configured as ST-Link (i.e. jumpers disconnected).

Any advice on why the SWV would not work in this second case is appreciated.

Regards,

Jonathan

[Tesla DeLorean]

With the NUCLEO you need to disconnect SWDIO, SWCLK and SWO from the on-board target, the first two via the jumpers that you've removed, the latter via a Solder Bridge (SB)

[jdawkins]

Hi - can you confirm which of the SWO solder bridges you are referring to? SB11 (through), SB10 (level shifter) or one of the reserved SBs?

[Tesla DeLorean]

Should be SB11, but looking at the schematic this is in the wrong location, and you might have to removed the level shifter or cut the trace out of it so it's not driving into T_SWO

@STTwo-32 please have someone review, SB11 disconnects input to level shifter, not the output

https://www.st.com/resource/en/schematic_pack/mb1319-l433rc_p-c02_schematic.pdf

[jdawkins]

I can confirm that with SB11 and both jumpers disconnected, SWO from an external STM32L432 does not work using the STLink on the MB1319-L433RC board..

Thanks for sharing the schematic. Are you suggesting to remove U6, or the output trace at Pin 3 (A2) so that it is not driving T_SWO to U2? SB10 is default disconnected (below) but with VDD_MCU and 3V3_ST_LINK being level, SWO also does not work with SB10 connected (and SB11 removed).

Thanks,

Jonathan

Edit: For what it's worth, I've verified the SWO trace is being produced by the target (external) MCU, so assured for now that it is indeed an STLink configuration issue.

--- Repeated from UM2206 --

SB10 - SWO level shifter by-pass 

ON SWO not connected through level shifter
OFF (default) SWO connected through level shifter to target MCU for 1.8 V I/O configuration

[Tesla DeLorean]

T_SWO is on the 6-pin header (CN3) as an INPUT

U6.3 (A2) OUTPUT conflicts with this from a signal derived from the on-board target. SB11 disconnects the INPUT to U6.6 (B2), SB10 bypasses, in the absence of U6. There's not clear way to disable direction/power to the chip. If you made SB10 U6 inputs/outputs at different voltages would conflict

Unfortunately U5/U6 are on the break-off section, so snapping off doesn't help.

Remove U6, or cut T_SWO trace so that it only connects between CN3 and U2

[jdawkins]

Removing U6 results in the ST-Link no longer being able to find the target (external) MCU.

[Tesla DeLorean]

Bridge T_JTMS / T_SWDIO_IN, or 100R at R23