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 pull-up */
  58         STXPORT |= (1 << STX);
  59         STXDDR  |= (1 << STX);
  60         SRXPORT |= (1 << SRX);
  61
  62         /* Enable INT0 for the detection of incoming 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         /* Clear reception channel ISR flag and enable the bit reception ISR */
  83         TIFR1  = (1 << OCF1A);
  84         TIMSK1 = (1 << OCIE1A);
  85
  86         /* Disable start bit detection ISR while the next byte is received */
  87         EIMSK &= ~(1 << INT0);
  88 }
  89
  90 /** ISR to manage the reception of bits to the software UART. */
  91 ISR(TIMER1_COMPA_vect, ISR_BLOCK)
  92 {
  93         /* Move the reception ISR compare position one bit ahead */
  94         OCR1A += BIT_TIME;
  95
  96         /* Check if reception has finished */
  97         if (RX_BitMask)
  98         {
  99                 /* Store next bit into the received data variable */
 100                 if (SRXPIN & (1 << SRX))
 101                   RX_Data |= RX_BitMask;
 102
 103                 /* Shift the current received bit mask to the next bit position */
 104                 RX_BitMask <<= 1;
 105         }
 106         else
 107         {
 108                 /* Reception complete, store the received byte */
 109                 RingBuffer_Insert(&UARTtoUSB_Buffer, RX_Data);
 110
 111                 /* Disable the reception ISR as all data has now been received, re-enable start bit detection ISR */
 112                 TIMSK1 = 0;
 113                 EIFR   = (1 << INTF0);
 114                 EIMSK  = (1 << INT0);
 115         }
 116 }
 117
 118 /** ISR to manage the transmission of bits via the software UART. */
 119 ISR(TIMER3_COMPA_vect, ISR_NOBLOCK)
 120 {
 121         /* Move the transmission ISR compare position one bit ahead */
 122         OCR3A += BIT_TIME;
 123
 124         /* Check if transmission has finished */
 125         if (TX_BitsRemaining)
 126         {
 127                 /* Check if we are sending a data bit, or the start bit */
 128                 if (--TX_BitsRemaining != 9)
 129                 {
 130                         /* Set the TX line to the value of the next bit in the byte to send */
 131                         if (TX_Data & (1 << 0))
 132                           STXPORT &= ~(1 << STX);
 133                         else
 134                           STXPORT |=  (1 << STX);
 135
 136                         /* Shift the transmission byte to move the next bit into position */
 137                         TX_Data >>= 1;
 138                 }
 139                 else
 140                 {
 141                         /* Start bit - keep TX line low */
 142                         STXPORT &= ~(1 << STX);
 143                 }
 144         }
 145         else if (USBtoUART_Buffer.Count)
 146         {
 147                 /* Transmission complete, get the next byte to send (if available) */
 148                 TX_Data = ~RingBuffer_Remove(&USBtoUART_Buffer);
 149                 TX_BitsRemaining = 10;
 150         }
 151 }