PDC_RNCR
if (bus_space_read_4(iot, ioh, offset + PDC_RNCR))
bus_space_write_4(iot, ioh, offset + PDC_RNCR, chunk_size);
bus_space_write_4(iot, ioh, offset + PDC_RNCR, 0);
PUTREG(sc, SPI_PDC_BASE + PDC_RNCR, 0);
PUTREG(sc, SPI_PDC_BASE + PDC_RNCR, len);
at91usart_writereg(sc, US_PDC + PDC_RNCR, 0);
at91usart_writereg(sc, US_PDC + PDC_RNCR, 0); \