firmware/s88w-r.c

   1 /* $Id$
   2
   3 This file is part of the MSP Märklin suite
   4 Copyright © 2010  Mikkosoft Productions, Mikko Rasa
   5 Distributed under the GPL
   6
   7 Firmware for wireless S88 receiver module
   8
   9 S88 pinout:
  10 1 - DATA
  11 2 - GND
  12 3 - CLOCK
  13 4 - LOAD
  14 5 - RESET
  15 6 - POWER
  16
  17 ATMega pinout:
  18 D0 - serial RX
  19 D1 - serial TX
  20 D2 - S88 DATA
  21 D3 - S88 CLOCK
  22 D4 - S88 LOAD
  23 D5 - S88 RESET
  24 */
  25
  26 #include <avr/io.h>
  27 #include <avr/interrupt.h>
  28
  29 #define DATA_OUT PORTD2
  30 #define CLOCK    PIND3
  31 #define LOAD     PIND4
  32 #define RESET    PIND5
  33
  34 #define BIT(n)   (1<<(n))
  35
  36 uint8_t decode_hex(uint8_t);
  37
  38 volatile uint8_t rx_buf[3];
  39 volatile uint8_t rx_fill = 0;
  40 volatile uint8_t input = 0;
  41 volatile uint8_t latch = 0;
  42
  43 int main()
  44 {
  45         uint8_t clock_high = 0;
  46         uint8_t bits = 0;
  47
  48         DDRD = 0x06;  // 00000110
  49         PIND = 0xC0;  // 11000000
  50         DDRB = 0x20;  // 00100000
  51         PINB = 0x1F;  // 00011111
  52
  53         // 9600 baud, 8N1
  54         UBRR0H = 0;
  55         UBRR0L = 103;
  56         UCSR0C = BIT(UCSZ00) | BIT(UCSZ01);
  57         UCSR0B = BIT(RXEN0) | BIT(TXEN0) | BIT(RXCIE0);
  58
  59         sei();
  60
  61         while(1)
  62         {
  63                 uint8_t d_pins;
  64
  65                 d_pins = PIND;
  66
  67                 if(d_pins&BIT(CLOCK))
  68                 {
  69                         if(!clock_high)
  70                         {
  71                                 if(d_pins&BIT(LOAD))
  72                                         bits = latch;
  73                                 else
  74                                         bits >>= 1;
  75
  76                                 if(bits&1)
  77                                         PORTD |= BIT(DATA_OUT);
  78                                 else
  79                                         PORTD &= ~BIT(DATA_OUT);
  80
  81                                 clock_high = 1;
  82                         }
  83                 }
  84                 else if(clock_high)
  85                         clock_high = 0;
  86
  87                 if(d_pins&BIT(RESET))
  88                         latch = input;
  89         }
  90 }
  91
  92 ISR(USART_RX_vect)
  93 {
  94         uint8_t c = UDR0;
  95         if(rx_fill==0)
  96         {
  97                 if(c==':')
  98                         rx_buf[rx_fill++] = c;
  99         }
 100         else
 101         {
 102                 rx_buf[rx_fill++] = c;
 103                 if(rx_buf[0]==':' && rx_fill==3)
 104                 {
 105                         input = (decode_hex(rx_buf[1])<<4) | decode_hex(rx_buf[2]);
 106                         latch |= input;
 107                         rx_fill = 0;
 108                 }
 109         }
 110 }
 111
 112 uint8_t decode_hex(uint8_t c)
 113 {
 114         if(c>='0' && c<='9')
 115                 return c-'0';
 116         else if(c>='A' && c<='F')
 117                 return 0xA+(c-'A');
 118         else
 119                 return 0;
 120 }