JTAG Daisy-Chaining

rezarethink
Posts: 20
Joined: Fri Mar 24, 2017 4:15 am

JTAG Daisy-Chaining

Postby rezarethink » Thu Aug 24, 2017 2:59 am

I'm planning on using the ESP32 along with an STM32. Is it possible to do JTAG daisy-chaining? And would both ICs need to be powered up for JTAG to work for either IC?

Thnx,
Reza

ESP_Sprite
Posts: 8921
Joined: Thu Nov 26, 2015 4:08 am

Re: JTAG Daisy-Chaining

Postby ESP_Sprite » Thu Aug 24, 2017 9:31 am

In theory, it should be possible to daisy-chain JTAG; the protocol is built for this. In designing the OpenOCD drivers, we've tried to take this scenario into account; however due to it not being a standard usage scenario, we can't guarantee we haven't missed something here or there. (If we did, feel free to report a bug and we'll fix it.) You do need to power both devices when you daisy-chain JTAG; the nature of the protocol makes it impossible for a powered-off device to pass along data in a compatible fashion.

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