common/spi_slave_spi.c

   1 /*
   2  * avrtest - A simple interface to usbtinyisp to act as a 'console'
   3  *           using SPI, target software to test for attiny84.
   4  * Copyright (C) 2008 Matt Anderson.
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation; either version 2 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program; if not, write to the Free Software
  18  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  19  */
  20
  21 #include <stdint.h>
  22
  23 #include <avr/io.h>
  24 #include <avr/interrupt.h>
  25 #include <avr/power.h>
  26
  27 #include "spislave.h"
  28
  29 #define NUM_BUFFER_BYTES 32
  30
  31 struct buffer_type
  32 {
  33   uint8_t buf[NUM_BUFFER_BYTES];
  34   uint8_t cur;
  35   uint8_t len;
  36 };
  37
  38 static volatile struct buffer_type tx, rx;
  39
  40 ISR(SIG_SPI)
  41 {
  // If byte in USIDR is non zero and space is available in the
  42   // rx queue, read byte from USIDR and place in rx queue.
  43   uint8_t spdr = SPDR;
  44   if (spdr && rx.len < NUM_BUFFER_BYTES)
  45   {
  46     uint8_t pos = rx.cur + rx.len;
  47     while (pos >= NUM_BUFFER_BYTES) {
  48       pos -= NUM_BUFFER_BYTES;
  49     }
  50     rx.buf[pos] = spdr;
  51     ++rx.len;
  52   }
  53
  54   // If bytes are pending in the tx queue place in USIDR.
  55   if (tx.len)
  56   {
  57     SPDR = tx.buf[tx.cur];
  58
  59     uint8_t cur = tx.cur+1;
  60     while (cur >= NUM_BUFFER_BYTES) {
  61       cur -= NUM_BUFFER_BYTES;
  62     }
  63     tx.cur = cur;
  64
  65     --tx.len;
  66   }
  67
  68   // Otherwise clear USIDR.
  69   else
  70     SPDR = 0;
  71
  72 }
  73
  74 void
  75 spi_slave_init(void)
  76 {
  77   power_spi_enable();
  78   // Enable three wire mode, external positive edge clock,
  79   // Interrupt on counter overflow
  80   // Interupt, enable, msb first, slave, leading edge on rise, sample on leading edge.
  81
  82
  83   DDRB&=~(1<<5)|(1<<7)|(1<<4); // inputs
  84   DDRB|= (1<<6);        // outputs
  85   PORTB&=~(1<<5)|(1<<7)|(1<<4)|(1<<6); // disable pullups & start low
  86   SPCR = (1<<SPIE) | (1<<SPE) | (1 << DORD) | (0 << MSTR) | (0 << CPOL) | (0 << CPHA);
  87   SPDR = 0;
  88 }
  89
  90 #include <spi_slave_common.c>