JTAG TCK on Intel X Scale (ArmV5) PXA270
Reverse Engineering Asked on December 2, 2021
Is TCK on JTAG the same speed as CPU clock on a Intel X Scale (ArmV5) PXA270?
I’m probing signals on pads around the CPU and got a waveform like:
But I don’t know whether any of this data is JTAG, or just writing to memory or something else. Any idea what this data is?
I think if I can find TCK, TDO/TDI should be somewhere near the same set of pads on the PCB?
One Answer
No, TCK doesn’t have to match the CPU clock. In fact its usual speed is in kilohertz, not megahertz. However, you likely won’t see it in the oscilloscope or logic analyzer because it is driven by the JTAG probe and not the CPU. Discovering the JTAG pins requires active probing using something like JTAGulator, you are unlikely to find it via passive observation.
Answered by Igor Skochinsky on December 2, 2021
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