converter/x68k_usb/x68k.c

   1 /*
   2 Copyright 2012 Jun WAKO <wakojun@gmail.com>
   3
   4 This software is licensed with a Modified BSD License.
   5 All of this is supposed to be Free Software, Open Source, DFSG-free,
   6 GPL-compatible, and OK to use in both free and proprietary applications.
   7 Additions and corrections to this file are welcome.
   8
   9
  10 Redistribution and use in source and binary forms, with or without
  11 modification, are permitted provided that the following conditions are met:
  12
  13 * Redistributions of source code must retain the above copyright
  14   notice, this list of conditions and the following disclaimer.
  15
  16 * Redistributions in binary form must reproduce the above copyright
  17   notice, this list of conditions and the following disclaimer in
  18   the documentation and/or other materials provided with the
  19   distribution.
  20
  21 * Neither the name of the copyright holders nor the names of
  22   contributors may be used to endorse or promote products derived
  23   from this software without specific prior written permission.
  24
  25 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  26 AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  27 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  28 ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
  29 LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  30 CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  31 SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  32 INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  33 CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  34 ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  35 POSSIBILITY OF SUCH DAMAGE.
  36 */
  37
  38 #include <stdbool.h>
  39 #include <avr/io.h>
  40 #include <avr/interrupt.h>
  41 #include "x68k.h"
  42
  43
  44 void x68k_init(void)
  45 {
  46     KBD_RX_INIT();
  47 }
  48
  49 // RX ring buffer
  50 #define RBUF_SIZE   8
  51 static uint8_t rbuf[RBUF_SIZE];
  52 static uint8_t rbuf_head = 0;
  53 static uint8_t rbuf_tail = 0;
  54
  55 uint8_t x68k_recv(void)
  56 {
  57     uint8_t data = 0;
  58     if (rbuf_head == rbuf_tail) {
  59         return 0;
  60     }
  61
  62     data = rbuf[rbuf_tail];
  63     rbuf_tail = (rbuf_tail + 1) % RBUF_SIZE;
  64     return data;
  65 }
  66
  67 // USART RX complete interrupt
  68 ISR(KBD_RX_VECT)
  69 {
  70     uint8_t next = (rbuf_head + 1) % RBUF_SIZE;
  71     if (next != rbuf_tail) {
  72         rbuf[rbuf_head] = KBD_RX_DATA;
  73         rbuf_head = next;
  74     }
  75 }