On February 27, 2018 2:42:25 AM PST, Matthias Welwarsky <matthias.welwar...@sysgo.com> wrote: >I'm guessing that the BUSY check was done to explicitly to avoid a JTAG >WAIT, >which was an error condition not long ago. It might still break with >SWD.
Ah, I didn’t know that WAIT was ever considered an error. From reading the ARM debug infrastructure spec, it looked more like a flow control mechanism. I see now that OpenOCD appears to enable ORUNDETECT (at least I think it does, based on dap_dp_init in arm_adi_v5.c). According to the ADI specification, SWD also has a WAIT response, which it issues in case a previous transaction is outstanding. It says just the same as JTAG: if WAIT is received, normally a debugger just resends the same transaction. Although using sticky overrun mode changes the format a bit so that WAIT is followed by a data packet, which it would not be with ORUNDETECT cleared, and you have to clear the sticky status bit. -- Christopher Head
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