u/BaconLegit

Hi, I’m bringing up a custom XMOS XU316 board and can’t get JTAG working.

Windows detects the XTAG-4 and the XMOS service is running, but:

xrun -l

returns:

No Available Devices Found

I also tried slower JTAG speeds and reset:

xrun -l --jtag-speed 100
xrun -l --jtag-speed 1000 --reset

Same result.

Measurements so far:

VREF_JTAG = 1.8V
TMS = 1.8V
TDI = 1.8V
TCK = 0V idle
TDO = ~0.02V idle, no short to GND/VREF
RST_N = ~2.2V
24 MHz oscillator OE = 1.8V
24 MHz oscillator OUT reads ~0.66V on DMM
Local XU316 decoupling caps have voltage

The suspicious part: RST_N is pulled to +3.3V through 10k, with a diode path to +3.3V and 4.7uF to GND. But VREF_JTAG is 1.8V. Additionally, I have made sure the 0.9V comes up before the 1.8V and 3.3V (which come up at the same time).

Hi, I’m bringing up a custom XMOS XU316 board and can’t get JTAG working.

Windows detects the XTAG-4 and the XMOS service is running, but:

xrun -l

returns:

No Available Devices Found

I also tried slower JTAG speeds and reset:

xrun -l --jtag-speed 100
xrun -l --jtag-speed 1000 --reset

Same result.

Measurements so far:

VREF_JTAG = 1.8V
TMS = 1.8V
TDI = 1.8V
TCK = 0V idle
TDO = ~0.02V idle, no short to GND/VREF
RST_N = ~2.2V
24 MHz oscillator OE = 1.8V
24 MHz oscillator OUT reads ~0.66V on DMM
Local XU316 decoupling caps have voltage

The suspicious part: RST_N is pulled to +3.3V through 10k, with a diode path to +3.3V and 4.7uF to GND. But VREF_JTAG is 1.8V.

Questions:

1. Should RST_N be pulled to the same 1.8V domain as VREF_JTAG?
2. Could the 3.3V reset pullup explain why xrun -l sees no target?
3. Is the 10k + 4.7uF reset RC too heavy for XTAG reset/debug?
4. Anything else obvious to check in power/clock/reset/JTAG?

I’ll attach screenshots of the reset circuit, oscillator, xSYS2/JTAG header, XU316 power, and PCB layout. Thanks.