JTAG for both SW Debug and HW Debug Test

Hi Experts,

I am currently architecting a mixed signal SoC containing a Cortex Mx core. We will have a single JTAG port that we want to use for both S/W debug and for H/W debug/test.  Examples of the H/W debug/test would be: Standard boundary scan (board test), plus internal test (INTEST, BIST, test mode selections/overrides etc)

I would therefore need two on-chip TAP controllers, and in principle I could simply chain them together (JTAG I/O -> H/W TAP -> ARM TAP -> JTAG I/O).  However, this would violate the JTAG standard, since when BYPASS was selected, the chain length would be 2 bits long instead of 1 (I think that there is a similar issue with the IDCODE instruction).

I assume that this is a problem that many people already solved, and was hoping that there was a recommended solution, or App note.

Thanks for any feedback.


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