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Serial Wire Debug AP access

Yogatheesan Varatharajah
Note: This was originally posted on 15th March 2011 at http://forums.arm.com

Please somebody help me with this issue.
I am trying to program the flash memory using Serial wire Debug in a  STM32L152 advanced ARM-based 32-bit MCU.
I will be almost done if this issue gets cleared. I am able to do read and write  accesses on each of the  DP registers if they actually allow to do so.And when I try to read one of the AP registers, it gives me  an 'OK' response.  But when I read the value, it gives all zeroes. After  that I tried to read the Read Buffer register. Still the same answer.  Also when I try to write one of the AP registers, it gives an 'OK'  response. Then I sent some 32 bits with a parity bit to be written. But  after that the 'STICKYERR' bit got set in the CTRL/STATUS register  with the data not being written I hope,which means some bus error has  occurred. What may be the problem? At least I should be able to do read  and write accesses in the CSW-AP register. Am I right? I thing I may not  be aware of some important issue. I would be very much grateful to you  if you could spend a little time in clarifying my doubt.

What is the importance of the Clock signal in AP access? Will it be a reason for the above issue?


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