this software.
*/
-#include "SoftUART.h"
+/** \file
+ *
+ * Software UART for both data transmission and reception. This
+ * code continuously monitors the ring buffers set up by the main
+ * project source file and reads/writes data as it becomes available.
+ */
-volatile bool srx_done;
-volatile uint8_t stx_count;
-static uint8_t srx_data, srx_mask, srx_tmp, stx_data;
+#include "SoftUART.h"
-void SoftUART_TxByte(uint8_t Byte)
-{
- while (stx_count);
+/** Total number of bits remaining to be sent in the current frame */
+static uint8_t TX_BitsRemaining;
- stx_data = ~Byte;
- stx_count = 10;
-}
+/** Temporary data variable to hold the byte being transmitted as it is shifted out */
+static uint8_t TX_Data;
-uint8_t SoftUART_RxByte(void)
-{
- while (!(srx_done));
- srx_done = false;
+/** Current bit mask of the bit being shifted into the received data byte */
+static uint8_t RX_BitMask;
- return srx_data;
-}
+/** Temporary data variable to hold the byte being received as it is shifted in */
+static uint8_t RX_Data;
+/** Initializes the software UART, ready for data transmission and reception into the global ring buffers. */
void SoftUART_Init(void)
{
- OCR2B = TCNT2 + 1; // force first compare
- TCCR2A = (1 << COM2B1) | (1 << COM2B0); // T1 mode 0
- TCCR2B = (1 << FOC2B) | (1 << CS21); // CLK/8, T1 mode 0
- TIMSK2 = (1 << OCIE2B); // enable tx and wait for start
- EICRA = (1 << ISC01); // -ve edge
- EIMSK = (1 << INT0); // enable INT0 interrupt
-
- stx_count = 0; // nothing to send
- srx_done = false; // nothing received
- STXPORT |= (1 << STX); // TX output
- STXDDR |= (1 << STX); // TX output
- SRXPORT |= (1 << SRX); // pullup on INT0
+ /* Set TX pin to output high, enable RX pull-up */
+ STXPORT |= (1 << STX);
+ STXDDR |= (1 << STX);
+ SRXPORT |= (1 << SRX);
+
+ /* Enable INT0 for the detection of incoming start bits that signal the start of a byte */
+ EICRA = (1 << ISC01);
+ EIMSK = (1 << INT0);
+
+ /* Start software UART transmission and reception timers */
+ TIMSK3 = (1 << OCIE3A);
+ TCCR3B = (1 << CS30);
+ TCCR1B = (1 << CS10);
}
-/* ISR to detect the start of a bit being sent from the transmitter. */
-ISR(INT0_vect)
+/** ISR to detect the start of a bit being sent to the software UART. */
+ISR(INT0_vect, ISR_BLOCK)
{
- OCR2A = TCNT2 + (BIT_TIME / 8 * 3 / 2); // scan 1.5 bits after start
+ /* Set reception channel to fire 1.5 bits past the beginning of the start bit */
+ OCR1A = TCNT1 + (BIT_TIME + (BIT_TIME / 2));
- srx_tmp = 0; // clear bit storage
- srx_mask = 1; // bit mask
+ /* Clear the received data temporary variable, reset the current received bit position mask */
+ RX_Data = 0;
+ RX_BitMask = (1 << 0);
- TIFR2 = (1 << OCF2A); // clear pending interrupt
+ /* Clear reception channel ISR flag and enable the bit reception ISR */
+ TIFR1 = (1 << OCF1A);
+ TIMSK1 = (1 << OCIE1A);
- if (!(SRXPIN & (1 << SRX))) // still low
- {
- TIMSK2 = (1 << OCIE2A) | (1 << OCIE2B); // wait for first bit
- EIMSK &= ~(1 << INT0);
- }
+ /* Disable start bit detection ISR while the next byte is received */
+ EIMSK &= ~(1 << INT0);
}
-/* ISR to manage the reception of bits to the transmitter. */
-ISR(TIMER2_COMPA_vect)
+/** ISR to manage the reception of bits to the software UART. */
+ISR(TIMER1_COMPA_vect, ISR_BLOCK)
{
- if (srx_mask)
+ /* Move the reception ISR compare position one bit ahead */
+ OCR1A += BIT_TIME;
+
+ /* Check if reception has finished */
+ if (RX_BitMask)
{
+ /* Store next bit into the received data variable */
if (SRXPIN & (1 << SRX))
- srx_tmp |= srx_mask;
+ RX_Data |= RX_BitMask;
- srx_mask <<= 1;
-
- OCR2A += BIT_TIME / 8; // next bit slice
+ /* Shift the current received bit mask to the next bit position */
+ RX_BitMask <<= 1;
}
else
{
- srx_done = true; // mark rx data valid
- srx_data = srx_tmp; // store rx data
- TIMSK2 = (1 << OCIE2B); // enable tx and wait for start
- EIMSK |= (1 << INT0); // enable START irq
- EIFR = (1 << INTF0); // clear any pending
+ /* Reception complete, store the received byte */
+ RingBuffer_Insert(&UARTtoUSB_Buffer, RX_Data);
+
+ /* Disable the reception ISR as all data has now been received, re-enable start bit detection ISR */
+ TIMSK1 = 0;
+ EIFR = (1 << INTF0);
+ EIMSK = (1 << INT0);
}
}
-/* ISR to manage the transmission of bits to the receiver. */
-ISR(TIMER2_COMPB_vect)
+/** ISR to manage the transmission of bits via the software UART. */
+ISR(TIMER3_COMPA_vect, ISR_NOBLOCK)
{
- OCR2B += BIT_TIME / 8; // next bit slice
+ /* Move the transmission ISR compare position one bit ahead */
+ OCR3A += BIT_TIME;
- if (stx_count)
+ /* Check if transmission has finished */
+ if (TX_BitsRemaining)
{
- if (--stx_count != 9) // no start bit
+ /* Check if we are sending a data bit, or the start bit */
+ if (--TX_BitsRemaining != 9)
{
- if (!(stx_data & 1)) // test inverted data
- TCCR2A = (1 << COM2B1) | (1 << COM2B0);
+ /* Set the TX line to the value of the next bit in the byte to send */
+ if (TX_Data & (1 << 0))
+ STXPORT &= ~(1 << STX);
else
- TCCR2A = (1 << COM2B1);
+ STXPORT |= (1 << STX);
- stx_data >>= 1; // shift zero in from left
+ /* Shift the transmission byte to move the next bit into position */
+ TX_Data >>= 1;
}
else
{
- TCCR2A = (1 << COM2B1); // START bit
+ /* Start bit - keep TX line low */
+ STXPORT &= ~(1 << STX);
}
}
+ else if (USBtoUART_Buffer.Count)
+ {
+ /* Transmission complete, get the next byte to send (if available) */
+ TX_Data = ~RingBuffer_Remove(&USBtoUART_Buffer);
+ TX_BitsRemaining = 10;
+ }
}
projects / pub / USBasp.git / blobdiff