DBGU_SR_RXRDY
if (sr & DBGU_SR_RXRDY) {
while (DBGUREG(DBGU_SR) & DBGU_SR_RXRDY
#define DBGU_PEEKC() ((DBGUREG(DBGU_SR) & DBGU_SR_RXRDY) ? DBGUREG(DBGU_RHR) : -1)