/*
- LUFA Library
- Copyright (C) Dean Camera, 2010.
-
+ LUFA Library
+ Copyright (C) Dean Camera, 2017.
+
dean [at] fourwalledcubicle [dot] com
- www.fourwalledcubicle.com
+ www.lufa-lib.org
*/
/*
Copyright 2010 David Prentice (david.prentice [at] farming [dot] uk)
Copyright 2010 Peter Danneger
- Copyright 2010 Dean Camera (dean [at] fourwalledcubicle [dot] com)
+ Copyright 2017 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
+ The author disclaims all warranties with regard to this
software, including all implied warranties of merchantability
and fitness. In no event shall the author be liable for any
special, indirect or consequential damages or any damages
/** 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. */
void SoftUART_Init(void)
{
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 to -(1/2) of the total bit time, so that the first data bit is
+ * sampled mid way through the total bit time, making reception more robust.
+ */
+ TCNT1 = -(OCR1A >> 1);
- /* Clear reception channel ISR flag and enable the bit reception ISR */
- TIFR1 = (1 << OCF1A);
- TIMSK1 = (1 << OCIE1A);
+ /* Check to see that the pin is still low (prevents glitches from starting a frame reception) */
+ if (!(SRXPIN & (1 << SRX)))
+ {
+ /* Disable start bit detection ISR while the next byte is received */
+ EIMSK = 0;
- /* Disable start bit detection ISR while the next byte is received */
- 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