Projects/XPLAINBridge/Lib/SoftUART.c

   1 /*
   2                          LUFA Library
   3          Copyright (C) Dean Camera, 2010.
   4
   5   dean [at] fourwalledcubicle [dot] com
   6           www.fourwalledcubicle.com
   7 */
   8
   9 /*
  10   Copyright 2010  David Prentice (david.prentice [at] farming [dot] uk)
  11   Copyright 2010  Peter Danneger
  12   Copyright 2010  Dean Camera (dean [at] fourwalledcubicle [dot] com)
  13
  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.
  22
  23   The author disclaim 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
  30   this software.
  31 */
  32
  33 /** \file
  34  *
  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.
  38  */
  39
  40 #include "SoftUART.h"
  41
  42 /** Total number of bits remaining to be sent in the current frame */
  43 static uint8_t TX_BitsRemaining;
  44
  45 /** Temporary data variable to hold the byte being transmitted as it is shifted out */
  46 static uint8_t TX_Data;
  47
  48 /** Current bit mask of the bit being shifted into the received data byte */
  49 static uint8_t RX_BitMask;
  50
  51 /** Temporary data variable to hold the byte being received as it is shifted in */
  52 static uint8_t RX_Data;
  53
  54 /** Initializes the software UART, ready for data transmission and reception into the global ring buffers. */
  55 void SoftUART_Init(void)
  56 {
  57         /* Set TX pin to output high, enable RX pullup */
  58         STXPORT |= (1 << STX);
  59         STXDDR  |= (1 << STX);
  60         SRXPORT |= (1 << SRX);
  61
  62         /* Enable INT0 for the detection of incomming start bits that signal the start of a byte */
  63         EICRA  = (1 << ISC01);
  64         EIMSK  = (1 << INT0);
  65
  66         /* Start software UART transmission and reception timers */
  67         TIMSK3 = (1 << OCIE3A);
  68         TCCR3B = (1 << CS30);
  69         TCCR1B = (1 << CS10);
  70 }
  71
  72 /** ISR to detect the start of a bit being sent to the software UART. */
  73 ISR(INT0_vect, ISR_BLOCK)
  74 {
  75         /* Set reception channel to fire 1.5 bits past the beginning of the start bit */
  76         OCR1A = TCNT1 + (BIT_TIME + (BIT_TIME / 2));
  77
  78         /* Clear the received data temporary variable, reset the current received bit position mask */
  79         RX_Data    = 0;
  80         RX_BitMask = (1 << 0);
  81
  82         /* Check that the start bit is still low to prevent noise from triggering a reception */
  83         if (!(SRXPIN & (1 << SRX)))
  84         {
  85                 /* Clear reception channel ISR flag in case it is pending */
  86                 TIFR1 = (1 << OCF1A);
  87
  88                 /* Still low, enable bit receive ISR */
  89                 TIMSK1 =  (1 << OCIE1A);
  90
  91                 /* Clear the start bit detection ISR flag */
  92                 EIMSK &= ~(1 << INT0);
  93         }
  94 }
  95
  96 /** ISR to manage the reception of bits to the software UART. */
  97 ISR(TIMER1_COMPA_vect, ISR_BLOCK)
  98 {
  99         /* Move the reception ISR compare position one bit ahead */
 100         OCR1A += BIT_TIME;
 101
 102         /* Check if reception has finished */
 103         if (RX_BitMask)
 104         {
 105                 /* Store next bit into the received data variable */
 106                 if (SRXPIN & (1 << SRX))
 107                   RX_Data |= RX_BitMask;
 108
 109                 /* Shift the current received bit mask to the next bit position */
 110                 RX_BitMask <<= 1;
 111         }
 112         else
 113         {
 114                 /* Reception complete, store the received byte */
 115                 RingBuffer_Insert(&UARTtoUSB_Buffer, RX_Data);
 116
 117                 /* Disable the reception ISR as all data has now been received, re-enable start bit detection ISR */
 118                 TIMSK1 = 0;
 119                 EIFR   = (1 << INTF0);
 120                 EIMSK  = (1 << INT0);
 121         }
 122 }
 123
 124 /** ISR to manage the transmission of bits via the software UART. */
 125 ISR(TIMER3_COMPA_vect, ISR_NOBLOCK)
 126 {
 127         /* Move the transmission ISR compare position one bit ahead */
 128         OCR3A += BIT_TIME;
 129
 130         /* Check if transmission has finished */
 131         if (TX_BitsRemaining)
 132         {
 133                 /* Check if we are sending a data bit, or the start bit */
 134                 if (--TX_BitsRemaining != 9)
 135                 {
 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);
 139                         else
 140                           STXPORT |=  (1 << STX);
 141
 142                         /* Shift the transmission byte to move the next bit into position */
 143                         TX_Data >>= 1;
 144                 }
 145                 else
 146                 {
 147                         /* Start bit - keep TX line low */
 148                         STXPORT &= ~(1 << STX);
 149                 }
 150         }
 151         else if (USBtoUART_Buffer.Count)
 152         {
 153                 /* Transmission complete, get the next byte to send (if available) */
 154                 TX_Data = ~RingBuffer_Remove(&USBtoUART_Buffer);
 155                 TX_BitsRemaining = 10;
 156         }
 157 }