/*
- LUFA Library
- Copyright (C) Dean Camera, 2010.
-
+ LUFA Library
+ Copyright (C) Dean Camera, 2010.
+
dean [at] fourwalledcubicle [dot] com
- www.fourwalledcubicle.com
+ www.lufa-lib.org
*/
/*
Copyright 2010 Peter Danneger
Copyright 2010 Dean Camera (dean [at] fourwalledcubicle [dot] com)
- Permission to use, copy, modify, distribute, and sell this
+ Permission to use, copy, modify, distribute, and sell this
software and its documentation for any purpose is hereby granted
- without fee, provided that the above copyright notice appear in
+ without fee, provided that the above copyright notice appear in
all copies and that both that the copyright notice and this
- permission notice and warranty disclaimer appear in supporting
- documentation, and that the name of the author not be used in
- advertising or publicity pertaining to distribution of the
+ permission notice and warranty disclaimer appear in supporting
+ documentation, and that the name of the author not be used in
+ advertising or publicity pertaining to distribution of the
software without specific, written prior permission.
The author disclaim all warranties with regard to this
#include "SoftUART.h"
-static uint8_t TX_BitsRemaining, TX_Data;
-static uint8_t RX_BitMask, RX_Data;
+/** Total number of bits remaining to be sent in the current frame */
+static uint8_t TX_BitsRemaining;
+
+/** Temporary data variable to hold the byte being transmitted as it is shifted out */
+static uint8_t TX_Data;
+
+/** Total number of bits remaining to be received in the current frame */
+static uint8_t RX_BitsRemaining;
+/** Temporary data variable to hold the byte being received as it is shifted in */
+static uint8_t RX_Data;
+
+/** Initialises the software UART, ready for data transmission and reception into the global ring buffers. */
void SoftUART_Init(void)
{
- OCR1B = TCNT1 + 1; // force first compare
- TCCR1B = (1 << CS10); // CLK/1, T1 mode 0
- TCCR1C = (1 << FOC1B);
- TIMSK1 = (1 << OCIE1B); // enable tx and wait for start
- EICRA = (1 << ISC01); // -ve edge
- EIMSK = (1 << INT0); // enable INT0 interrupt
-
- 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);
+
+ /* Set the transmission and reception timer compare values for the default baud rate */
+ SoftUART_SetBaud(9600);
+
+ /* Setup reception timer compare ISR */
+ TIMSK1 = (1 << OCIE1A);
+
+ /* Setup transmission timer compare ISR and start the timer */
+ TIMSK3 = (1 << OCIE3A);
+ TCCR3B = ((1 << CS30) | (1 << WGM32));
}
-/* ISR to detect the start of a bit being sent to the software UART. */
-ISR(INT0_vect)
+/** ISR to detect the start of a bit being sent to the software UART. */
+ISR(INT0_vect, ISR_BLOCK)
{
- OCR1A = TCNT1 + ((BIT_TIME * 3) / 2) - 1; // scan 1.5 bits after start
-
- RX_Data = 0; // clear bit storage
- RX_BitMask = (1 << 0); // bit mask
+ /* Reset the number of reception bits remaining counter */
+ RX_BitsRemaining = 8;
- TIFR1 = (1 << OCF1A); // clear pending interrupt
+ /* Reset the bit reception timer */
+ TCNT1 = 0;
- if (!(SRXPIN & (1 << SRX))) // still low
+ /* Check to see that the pin is still low (prevents glitches from starting a frame reception) */
+ if (!(SRXPIN & (1 << SRX)))
{
- TIMSK1 = (1 << OCIE1A) | (1 << OCIE1B); // wait for first bit
- EIMSK &= ~(1 << INT0);
+ /* Disable start bit detection ISR while the next byte is received */
+ EIMSK = 0;
+
+ /* Start the reception timer */
+ TCCR1B = ((1 << CS10) | (1 << WGM12));
}
}
-/* ISR to manage the reception of bits to the software UART. */
-ISR(TIMER1_COMPA_vect)
+/** ISR to manage the reception of bits to the software UART. */
+ISR(TIMER1_COMPA_vect, ISR_BLOCK)
{
- if (RX_BitMask)
- {
- if (SRXPIN & (1 << SRX))
- RX_Data |= RX_BitMask;
+ /* Cache the current RX pin value for later checking */
+ uint8_t SRX_Cached = (SRXPIN & (1 << SRX));
- RX_BitMask <<= 1;
+ /* Check if reception has finished */
+ if (RX_BitsRemaining)
+ {
+ /* Shift the current received bit mask to the next bit position */
+ RX_Data >>= 1;
+ RX_BitsRemaining--;
- OCR1A += BIT_TIME; // next bit slice
+ /* Store next bit into the received data variable */
+ if (SRX_Cached)
+ RX_Data |= (1 << 7);
}
else
{
- RingBuffer_Insert(&UARTtoUSB_Buffer, RX_Data);
-
- TIMSK1 = (1 << OCIE1B); // enable tx and wait for start
- EIMSK |= (1 << INT0); // enable START irq
- EIFR = (1 << INTF0); // clear any pending
+ /* Disable the reception timer as all data has now been received, re-enable start bit detection ISR */
+ TCCR1B = 0;
+ EIFR = (1 << INTF0);
+ EIMSK = (1 << INT0);
+
+ /* Reception complete, store the received byte if stop bit valid */
+ if (SRX_Cached)
+ RingBuffer_Insert(&UARTtoUSB_Buffer, RX_Data);
}
}
-/* ISR to manage the transmission of bits via the software UART. */
-ISR(TIMER1_COMPB_vect)
+/** ISR to manage the transmission of bits via the software UART. */
+ISR(TIMER3_COMPA_vect, ISR_BLOCK)
{
- OCR1B += BIT_TIME; // next bit slice
-
+ /* Check if transmission has finished */
if (TX_BitsRemaining)
{
- if (--TX_BitsRemaining != 9) // no start bit
- {
- if (TX_Data & (1 << 0)) // test inverted data
- STXPORT &= ~(1 << STX);
- else
- STXPORT = (1 << STX);
-
- TX_Data >>= 1; // shift zero in from left
- }
+ /* 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
- {
- STXPORT &= ~(1 << STX);
- }
+ STXPORT |= (1 << STX);
+
+ /* Shift the transmission byte to move the next bit into position and decrement the bits remaining counter */
+ TX_Data >>= 1;
+ TX_BitsRemaining--;
}
- else if (USBtoUART_Buffer.Count)
+ else if (!(RX_BitsRemaining) && !(RingBuffer_IsEmpty(&USBtoUART_Buffer)))
{
- TX_Data = ~RingBuffer_Remove(&USBtoUART_Buffer);
- TX_BitsRemaining = 10;
+ /* Start bit - TX line low */
+ STXPORT &= ~(1 << STX);
+
+ /* Transmission complete, get the next byte to send (if available) */
+ TX_Data = ~RingBuffer_Remove(&USBtoUART_Buffer);
+ TX_BitsRemaining = 9;
}
-}
+}
+
projects / pub / USBasp.git / blobdiff