3 Copyright (C) Dean Camera, 2014.
5 dean [at] fourwalledcubicle [dot] com
10 Copyright 2010 David Prentice (david.prentice [at] farming [dot] uk)
11 Copyright 2010 Peter Danneger
12 Copyright 2014 Dean Camera (dean [at] fourwalledcubicle [dot] com)
14 Permission to use, copy, modify, distribute, and sell this
15 software and its documentation for any purpose is hereby granted
16 without fee, provided that the above copyright notice appear in
17 all copies and that both that the copyright notice and this
18 permission notice and warranty disclaimer appear in supporting
19 documentation, and that the name of the author not be used in
20 advertising or publicity pertaining to distribution of the
21 software without specific, written prior permission.
23 The author disclaims all warranties with regard to this
24 software, including all implied warranties of merchantability
25 and fitness. In no event shall the author be liable for any
26 special, indirect or consequential damages or any damages
27 whatsoever resulting from loss of use, data or profits, whether
28 in an action of contract, negligence or other tortious action,
29 arising out of or in connection with the use or performance of
35 * Software UART for both data transmission and reception. This
36 * code continuously monitors the ring buffers set up by the main
37 * project source file and reads/writes data as it becomes available.
42 /** Total number of bits remaining to be sent in the current frame */
43 static uint8_t TX_BitsRemaining;
45 /** Temporary data variable to hold the byte being transmitted as it is shifted out */
46 static uint8_t TX_Data;
48 /** Total number of bits remaining to be received in the current frame */
49 static uint8_t RX_BitsRemaining;
51 /** Temporary data variable to hold the byte being received as it is shifted in */
52 static uint8_t RX_Data;
55 /** Initializes the software UART, ready for data transmission and reception into the global ring buffers. */
56 void SoftUART_Init(void)
58 /* Set TX pin to output high, enable RX pull-up */
59 STXPORT |= (1 << STX);
61 SRXPORT |= (1 << SRX);
63 /* Enable INT0 for the detection of incoming start bits that signal the start of a byte */
67 /* Set the transmission and reception timer compare values for the default baud rate */
68 SoftUART_SetBaud(9600);
70 /* Setup reception timer compare ISR */
71 TIMSK1 = (1 << OCIE1A);
73 /* Setup transmission timer compare ISR and start the timer */
74 TIMSK3 = (1 << OCIE3A);
75 TCCR3B = ((1 << CS30) | (1 << WGM32));
78 /** ISR to detect the start of a bit being sent to the software UART. */
79 ISR(INT0_vect, ISR_BLOCK)
81 /* Reset the number of reception bits remaining counter */
84 /* Reset the bit reception timer to -(1/2) of the total bit time, so that the first data bit is
85 * sampled mid way through the total bit time, making reception more robust.
87 TCNT1 = -(OCR1A >> 1);
89 /* Check to see that the pin is still low (prevents glitches from starting a frame reception) */
90 if (!(SRXPIN & (1 << SRX)))
92 /* Disable start bit detection ISR while the next byte is received */
95 /* Start the reception timer */
96 TCCR1B = ((1 << CS10) | (1 << WGM12));
100 /** ISR to manage the reception of bits to the software UART. */
101 ISR(TIMER1_COMPA_vect, ISR_BLOCK)
103 /* Cache the current RX pin value for later checking */
104 uint8_t SRX_Cached = (SRXPIN & (1 << SRX));
106 /* Check if reception has finished */
107 if (RX_BitsRemaining)
109 /* Shift the current received bit mask to the next bit position */
113 /* Store next bit into the received data variable */
119 /* Disable the reception timer as all data has now been received, re-enable start bit detection ISR */
124 /* Reception complete, store the received byte if stop bit valid */
126 RingBuffer_Insert(&UARTtoUSB_Buffer, RX_Data);
130 /** ISR to manage the transmission of bits via the software UART. */
131 ISR(TIMER3_COMPA_vect, ISR_BLOCK)
133 /* Check if transmission has finished */
134 if (TX_BitsRemaining)
136 /* Set the TX line to the value of the next bit in the byte to send */
137 if (TX_Data & (1 << 0))
138 STXPORT &= ~(1 << STX);
140 STXPORT |= (1 << STX);
142 /* Shift the transmission byte to move the next bit into position and decrement the bits remaining counter */
146 else if (!(RX_BitsRemaining) && !(RingBuffer_IsEmpty(&USBtoUART_Buffer)))
148 /* Start bit - TX line low */
149 STXPORT &= ~(1 << STX);
151 /* Transmission complete, get the next byte to send (if available) */
152 TX_Data = ~RingBuffer_Remove(&USBtoUART_Buffer);
153 TX_BitsRemaining = 9;