/*
- 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
/** Temporary data variable to hold the byte being transmitted as it is shifted out */
static uint8_t TX_Data;
-/** Current bit mask of the bit being shifted into the received data byte */
-static uint8_t RX_BitMask;
+/** 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;
-/** Initializes the software UART, ready for data transmission and reception into the global ring buffers. */
+/** Initialises the software UART, ready for data transmission and reception into the global ring buffers. */
void SoftUART_Init(void)
{
- /* Set TX pin to output high, enable RX pullup */
+ /* 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 incomming start bits that signal the start of a byte */
+ /* 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 */
+ /* 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);
- TCCR1B = (1 << CS10);
+ TCCR3B = ((1 << CS30) | (1 << WGM32));
}
/** ISR to detect the start of a bit being sent to the software UART. */
ISR(INT0_vect, ISR_BLOCK)
{
- /* Set reception channel to fire 1.5 bits past the beginning of the start bit */
- OCR1A = TCNT1 + (BIT_TIME + (BIT_TIME / 2));
+ /* Reset the number of reception bits remaining counter */
+ RX_BitsRemaining = 8;
- /* Clear the received data temporary variable, reset the current received bit position mask */
- RX_Data = 0;
- RX_BitMask = (1 << 0);
+ /* Reset the bit reception timer */
+ TCNT1 = 0;
- /* Check that the start bit is still low to prevent noise from triggering a reception */
+ /* Check to see that the pin is still low (prevents glitches from starting a frame reception) */
if (!(SRXPIN & (1 << SRX)))
{
- /* Clear reception channel ISR flag in case it is pending */
- TIFR1 = (1 << OCF1A);
-
- /* Still low, enable bit receive ISR */
- TIMSK1 = (1 << OCIE1A);
+ /* Disable start bit detection ISR while the next byte is received */
+ EIMSK = 0;
- /* Clear the start bit detection ISR flag */
- EIMSK &= ~(1 << INT0);
+ /* 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_BLOCK)
{
- /* Move the reception ISR compare position one bit ahead */
- OCR1A += BIT_TIME;
+ /* Cache the current RX pin value for later checking */
+ uint8_t SRX_Cached = (SRXPIN & (1 << SRX));
/* Check if reception has finished */
- if (RX_BitMask)
+ if (RX_BitsRemaining)
{
- /* Store next bit into the received data variable */
- if (SRXPIN & (1 << SRX))
- RX_Data |= RX_BitMask;
-
/* Shift the current received bit mask to the next bit position */
- RX_BitMask <<= 1;
+ RX_Data >>= 1;
+ RX_BitsRemaining--;
+
+ /* Store next bit into the received data variable */
+ if (SRX_Cached)
+ RX_Data |= (1 << 7);
}
else
{
- /* 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;
+ /* 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(TIMER3_COMPA_vect, ISR_NOBLOCK)
+ISR(TIMER3_COMPA_vect, ISR_BLOCK)
{
- /* Move the transmission ISR compare position one bit ahead */
- OCR3A += BIT_TIME;
-
/* Check if transmission has finished */
if (TX_BitsRemaining)
{
- /* Check if we are sending a data bit, or the start bit */
- if (--TX_BitsRemaining != 9)
- {
- /* 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);
-
- /* Shift the transmission byte to move the next bit into position */
- TX_Data >>= 1;
- }
+ /* 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
- {
- /* Start bit - keep TX line low */
- 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)))
{
+ /* 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 = 10;
+ TX_Data = ~RingBuffer_Remove(&USBtoUART_Buffer);
+ TX_BitsRemaining = 9;
}
-}
+}
+
projects / pub / USBasp.git / blobdiff