Projects/XPLAINBridge/Lib/SoftUART.c

   1 /*
   2              LUFA Library
   3      Copyright (C) Dean Camera, 2013.
   4
   5   dean [at] fourwalledcubicle [dot] com
   6            www.lufa-lib.org
   7 */
   8
   9 /*
  10   Copyright 2010  David Prentice (david.prentice [at] farming [dot] uk)
  11   Copyright 2010  Peter Danneger
  12   Copyright 2013  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 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
  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 /** Total number of bits remaining to be received in the current frame */
  49 static uint8_t RX_BitsRemaining;
  50
  51 /** Temporary data variable to hold the byte being received as it is shifted in */
  52 static uint8_t RX_Data;
  53
  54
  55 /** Initializes the software UART, ready for data transmission and reception into the global ring buffers. */
  56 void SoftUART_Init(void)
  57 {
  58         /* Set TX pin to output high, enable RX pull-up */
  59         STXPORT |= (1 << STX);
  60         STXDDR  |= (1 << STX);
  61         SRXPORT |= (1 << SRX);
  62
  63         /* Enable INT0 for the detection of incoming start bits that signal the start of a byte */
  64         EICRA  = (1 << ISC01);
  65         EIMSK  = (1 << INT0);
  66
  67         /* Set the transmission and reception timer compare values for the default baud rate */
  68         SoftUART_SetBaud(9600);
  69
  70         /* Setup reception timer compare ISR */
  71         TIMSK1 = (1 << OCIE1A);
  72
  73         /* Setup transmission timer compare ISR and start the timer */
  74         TIMSK3 = (1 << OCIE3A);
  75         TCCR3B = ((1 << CS30) | (1 << WGM32));
  76 }
  77
  78 /** ISR to detect the start of a bit being sent to the software UART. */
  79 ISR(INT0_vect, ISR_BLOCK)
  80 {
  81         /* Reset the number of reception bits remaining counter */
  82         RX_BitsRemaining = 8;
  83
  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.
  86          */
  87         TCNT1 = -(OCR1A >> 1);
  88
  89         /* Check to see that the pin is still low (prevents glitches from starting a frame reception) */
  90         if (!(SRXPIN & (1 << SRX)))
  91         {
  92                 /* Disable start bit detection ISR while the next byte is received */
  93                 EIMSK = 0;
  94
  95                 /* Start the reception timer */
  96                 TCCR1B = ((1 << CS10) | (1 << WGM12));
  97         }
  98 }
  99
 100 /** ISR to manage the reception of bits to the software UART. */
 101 ISR(TIMER1_COMPA_vect, ISR_BLOCK)
 102 {
 103         /* Cache the current RX pin value for later checking */
 104         uint8_t SRX_Cached = (SRXPIN & (1 << SRX));
 105
 106         /* Check if reception has finished */
 107         if (RX_BitsRemaining)
 108         {
 109                 /* Shift the current received bit mask to the next bit position */
 110                 RX_Data >>= 1;
 111                 RX_BitsRemaining--;
 112
 113                 /* Store next bit into the received data variable */
 114                 if (SRX_Cached)
 115                   RX_Data |= (1 << 7);
 116         }
 117         else
 118         {
 119                 /* Disable the reception timer as all data has now been received, re-enable start bit detection ISR */
 120                 TCCR1B = 0;
 121                 EIFR   = (1 << INTF0);
 122                 EIMSK  = (1 << INT0);
 123
 124                 /* Reception complete, store the received byte if stop bit valid */
 125                 if (SRX_Cached)
 126                   RingBuffer_Insert(&UARTtoUSB_Buffer, RX_Data);
 127         }
 128 }
 129
 130 /** ISR to manage the transmission of bits via the software UART. */
 131 ISR(TIMER3_COMPA_vect, ISR_BLOCK)
 132 {
 133         /* Check if transmission has finished */
 134         if (TX_BitsRemaining)
 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 and decrement the bits remaining counter */
 143                 TX_Data >>= 1;
 144                 TX_BitsRemaining--;
 145         }
 146         else if (!(RX_BitsRemaining) && !(RingBuffer_IsEmpty(&USBtoUART_Buffer)))
 147         {
 148                 /* Start bit - TX line low */
 149                 STXPORT &= ~(1 << STX);
 150
 151                 /* Transmission complete, get the next byte to send (if available) */
 152                 TX_Data          = ~RingBuffer_Remove(&USBtoUART_Buffer);
 153                 TX_BitsRemaining = 9;
 154         }
 155 }
 156