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6 years, 5 months ago.
SWDAP fails with M4 device
The SWDAP hardware didn't work for my Cortex M4F processor in the PAC5523 from Active-Semi.com. The problem appears with Keil, IAR, and OpenOCD. The DAPLINK code does the following: 50 1s reset JTAG to SWD swtich sequence 50 1s reset IDCODE read But, when it tries to read the IDCODE, the M4F responds with an ack of 5 or b101, which is not a valid ack response. So, this leads me to believe the JTAG to SWD switch didn't take. The signals on an oscilloscope seem to look fine, but it wasn't working.
I ran the same DAPLINK code on the IBDAP, and everything worked. The IBDAP also uses the LPC11u35. So, I suspected the SWDAP's 470R series resistors on the SWDIO and SWCLK signals. After I replaced them with 33R, now it works. The IBDAP uses 33R series resistors.
Has anyone else seen issues like this?
Also, I've seen other SWD debugger designs that use 22R series resistors. So, perhaps lower series resistor values may help the SWDAP work across more devices.