I definitely don't miss it while writing my own code. In porting well, I think because we've got volatile flag nonsense, we need to do some significant surgery to even make this compile anyway, and so perhaps

  do { ... } while (((data & DAP_Data.transfer.match_mask) != match_value) && match_retry-- && !DAP_TransferAbort);

becomes something like

  loop {
    ...
    if data & DAP_Data.transfer.match_mask) == match_value {
      break;
    }
    match_retry -= 1;
    if match_retry == 0 {
      break;
    }
    if check_transfer_abort() { // Replaces DAP_TransferAbort
      break;
    }
  }

I think that's actually more clear, and my mental focus is DAP_TransferAbort. I think it's just C programmers being C programmers, and we just want AtomicBool for this but I'm more comfortable wrapping it in this check_transfer_abort() function while I investigate whether anybody thinks this is a counter, or there's actually physical hardware backing it despite the way it looks like it's just a global variable.