blueskull / ch552-jtag Goto Github PK

Hi blueskull.

First thanks for your work which has implemented a passthrough protocol of JTAG and gives much more flexibility.
Here I get a bit of confusion while I am reading the macro jtag_bit_read(mask) and hope you could give some claification.

Refer to IEEE Std 1149.1-2001 p20 "TDO shall occur only on the falling edge of TCK" which means after a falling edge of TCK, the output bit will be shifted out on the TDO then host can read it.

#define jtag_bit_read(mask) {TMS = tms & mask; TDI = tdi & mask; SAFE_MOD++; tdo |= TDO ? mask : 0; TCK = 1; TCK = 0;}

Here TDO is read before the falling edge (TCK=0), so if it is an issue? If so it shouldn't work, however, as you said it worked for GowinFPGA. Thanks in advance.