ARM-USB-OCD required pins for JTAG connection

[steelfly]

I have a controller board that I have toned out TDI, TDO, TMS, and TCLK.  Through another JTAG interface, I can get the JTAG ids of the three devices on the JTAG chain.

When I connect the board to the Olimex ARM-USB-OCD and use open-ocd to auto-probe, it tells me "JTAG scan chain interrogation failed: all zeros".  I have the four mentioned lines and GND connected to the Olimex.  Do I need additional lines connected?

I tried connecting VREF to both GND and VCC.  When connected to GND, I get the same response (no surprise).  When I connect VREF to VCC, open-ocd tells me "JTAG scan chain interrogation failed: all ones".  I figure I have to be missing some obvious connection or setting?

Any help is appreciated...
Thanks,
-- Brian

[LubOlimex]

Hey steelfly,

Do you connect the reset? What reset strategy do you use in OpenOCD?

Is it possible to check the schematics of one of our ARM boards to be sure you connect everything correct? For instance - you might refer to the schematics of the open-hardware STM32-H407: https://www.olimex.com/Products/ARM/ST/STM32-H407/.

The layout of the connector might be seen here: https://www.olimex.com/Products/ARM/JTAG/_resources/ARM-USB-OCD.pdf

Best regards,
Lub/OLIMEX

[steelfly]

I now connect RST but see no difference.  I have not yet gotten to the reset strategy in openOCD because I haven't been able to connect to any devices on the JTAG chain using the Olimex.

I have connected other devices via the Olimex and been able to communicate to them using openOCD.

This one device does not seem to cooperate using the Olimex.  If I connect Joe Grand's JTAGulator, it verifies the JTAG pins and successfully queries for the id of each device on the chain.  When I connect TDI, TMS, TCK, TDO, RST, VREF, and GND via the Olimex, I still get "JTAG scan chain interrogation failed: all zeros".

[LubOlimex]

Hey steelfly,

Is it possible that you have some weird code on the microcontroller that changes pinouts very fast after power-up or disables interrupts? Is it possible to program another memory of the microcontroller?

There is a lot written about the "JTAG scan chain interrogation failed: all zeros error". You might want to Google the error and check some solutions.

Best regards,
Lub/OLIMEX