static void tx_ack() {
// wait for ack timeslot
last_frame_end += TAG_ACK_WAIT;
legic_prng_forward(TAG_ACK_WAIT/TAG_BIT_PERIOD - 1);
while(GetCountSspClk() < last_frame_end) { };
// transmit ack (ack is not encrypted)
tx_bit(true);
legic_prng_forward(1);
// disable subcarrier
LOW(GPIO_SSC_DOUT);
}
unsigned char spi_slow_wr(register unsigned char data)
{
register int cnt;
for (cnt = 0; cnt < 8; cnt++) {
tx_bit(data & MSB);
delay1u5();
cts_bit(1); /* SPI clock ON */
data = (data << 1) | rx_bit(); /* SPI data input */
delay1u5();
cts_bit(0); /* SPI clock OFF */
}
return(data);
}
static void tx_frame(uint32_t frame, uint8_t len) {
// wait for next tx timeslot
last_frame_end += TAG_FRAME_WAIT;
legic_prng_forward(TAG_FRAME_WAIT/TAG_BIT_PERIOD - 1);
while(GetCountSspClk() < last_frame_end) { };
// transmit frame, MSB first
for(uint8_t i = 0; i < len; ++i) {
bool bit = (frame >> i) & 0x01;
tx_bit(bit ^ legic_prng_get_bit());
legic_prng_forward(1);
};
// disable subcarrier
LOW(GPIO_SSC_DOUT);
}
