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JTAG-DP in STM32F407: read+ APACC instruction returns zero

Question asked by pyka.natalia on Mar 9, 2014
Latest reply on Jun 24, 2016 by joseph.lijita
Hello everyone,

I use STM32F407 Discovery's JTAG-DP port controlled by basic TAP pins in my master thesis. I want to read access point's identification register (IDR) whose address is 0xFC.

That's what I do, basing on  ARM Debug Interface Architecture Specification ADIv5.0, p.1-25:

1) Having DPACC instruction loaded into TAP's instruction register, I choose the SELECT register and set SELECT.APBANKSEL to 0xF and SELECT.APSEL to 0x00.
2) I switch to APACC instruction.
3) I use AP register access with A[3:2]=0b11 + read operation.

As far as I understand the abovementioned description, these steps should led to a successful read of the ID register. However, each read returns ACK signal and all-zeros.

Did you have any similar problems or did I forget about some obvious operation? If yes - what should I do to enable the read operation?

Best regards,
Natalie

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