forked from mfulz_github/qmk_firmware
Add better documentation to the Software UART code in the XPLAINBridge project.
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Dean Camera
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1c407b9669
commit
bb9fb1051c
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@ -39,85 +39,121 @@
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#include "SoftUART.h"
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static uint8_t TX_BitsRemaining, TX_Data;
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static uint8_t RX_BitMask, RX_Data;
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/** Total number of bits remaining to be sent in the current frame */
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static uint8_t TX_BitsRemaining
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/** Temporary data variable to hold the byte being transmitted as it is shifted out */
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static uint8_t TX_Data;
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/** Current bit mask of the bit being shifted into the received data byte */
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static uint8_t RX_BitMask;
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/** Temporary data variable to hold the byte being received as it is shifted in */
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static uint8_t RX_Data;
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/** Initializes the software UART, ready for data transmission and reception into the global ring buffers. */
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void SoftUART_Init(void)
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{
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OCR1B = TCNT1 + 1; // force first compare
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TCCR1B = (1 << CS10); // CLK/1, T1 mode 0
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TCCR1C = (1 << FOC1B);
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TIMSK1 = (1 << OCIE1B); // enable tx and wait for start
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EICRA = (1 << ISC01); // -ve edge
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EIMSK = (1 << INT0); // enable INT0 interrupt
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/* Set TX pin to output high, enable RX pullup */
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STXPORT |= (1 << STX);
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STXDDR |= (1 << STX);
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SRXPORT |= (1 << SRX);
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STXPORT |= (1 << STX); // TX output
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STXDDR |= (1 << STX); // TX output
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SRXPORT |= (1 << SRX); // pullup on INT0
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/* Enable INT0 for the detection of incomming start bits that signal the start of a byte */
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EICRA = (1 << ISC01);
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EIMSK = (1 << INT0);
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/* Ensure that when the timer is enabled the transmission ISR runs immediately */
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OCR1B = TCNT1 + 1;
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/* Start timer 1 with transmission channel force-enabled so that it will immediatly fire */
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TCCR1C = (1 << FOC1B);
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TIMSK1 = (1 << OCIE1B);
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TCCR1B = (1 << CS10);
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}
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/* ISR to detect the start of a bit being sent to the software UART. */
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/** ISR to detect the start of a bit being sent to the software UART. */
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ISR(INT0_vect)
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{
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OCR1A = TCNT1 + ((BIT_TIME * 3) / 2) - 1; // scan 1.5 bits after start
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/* Set reception channel to fire 1.5 bits past the beginning of the start bit */
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OCR1A = TCNT1 + ((BIT_TIME * 3) / 2) - 1;
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/* Clear the received data temporary variable, reset the current received bit position mask */
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RX_Data = 0;
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RX_BitMask = (1 << 0);
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RX_Data = 0; // clear bit storage
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RX_BitMask = (1 << 0); // bit mask
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/* Clear reception channel ISR flag in case it is pending */
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TIFR1 = (1 << OCF1A);
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TIFR1 = (1 << OCF1A); // clear pending interrupt
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if (!(SRXPIN & (1 << SRX))) // still low
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{
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TIMSK1 = (1 << OCIE1A) | (1 << OCIE1B); // wait for first bit
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/* Check that the start bit is still low to prevent noise from triggering a reception */
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if (!(SRXPIN & (1 << SRX)))
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{
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/* Still low, enable both send and receive channels */
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TIMSK1 = (1 << OCIE1A) | (1 << OCIE1B);
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/* Clear the start bit detection ISR flag if it is pending */
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EIMSK &= ~(1 << INT0);
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}
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}
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/* ISR to manage the reception of bits to the software UART. */
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/** ISR to manage the reception of bits to the software UART. */
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ISR(TIMER1_COMPA_vect)
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{
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/* Move the reception ISR compare position one bit ahead */
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OCR1A += BIT_TIME;
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/* Check if reception has finished */
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if (RX_BitMask)
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{
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/* Store next bit into the received data variable */
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if (SRXPIN & (1 << SRX))
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RX_Data |= RX_BitMask;
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/* Shift the current received bit mask to the next bit position */
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RX_BitMask <<= 1;
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OCR1A += BIT_TIME; // next bit slice
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}
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else
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{
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/* Reception complete, store the received byte */
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RingBuffer_Insert(&UARTtoUSB_Buffer, RX_Data);
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TIMSK1 = (1 << OCIE1B); // enable tx and wait for start
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EIMSK |= (1 << INT0); // enable START irq
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EIFR = (1 << INTF0); // clear any pending
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/* Disable the reception ISR as all data has now been received, re-enable start bit detection ISR */
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TIMSK1 = (1 << OCIE1B);
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EIMSK |= (1 << INT0);
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EIFR = (1 << INTF0);
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}
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}
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/* ISR to manage the transmission of bits via the software UART. */
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/** ISR to manage the transmission of bits via the software UART. */
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ISR(TIMER1_COMPB_vect)
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{
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OCR1B += BIT_TIME; // next bit slice
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/* Move the transmission ISR compare position one bit ahead */
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OCR1B += BIT_TIME;
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/* Check if transmission has finished */
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if (TX_BitsRemaining)
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{
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if (--TX_BitsRemaining != 9) // no start bit
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/* Check if we are sending a data bit, or the start bit */
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if (--TX_BitsRemaining != 9)
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{
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if (TX_Data & (1 << 0)) // test inverted data
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/* Set the TX line to the value of the next bit in the byte to send */
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if (TX_Data & (1 << 0))
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STXPORT &= ~(1 << STX);
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else
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STXPORT = (1 << STX);
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STXPORT |= (1 << STX);
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TX_Data >>= 1; // shift zero in from left
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/* Shift the transmission byte to move the next bit into position */
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TX_Data >>= 1;
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}
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else
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{
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/* Start bit - keep TX line low */
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STXPORT &= ~(1 << STX);
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}
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}
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else if (USBtoUART_Buffer.Count)
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{
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/* Transmission complete, get the next byte to send (if available) */
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TX_Data = ~RingBuffer_Remove(&USBtoUART_Buffer);
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TX_BitsRemaining = 10;
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}
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