mpu401.c

/*
   Library to access MPU-401 hardware

   Copyright (c) 2014,2015, Mateusz Viste
   All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice,
   this list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice,
   this list of conditions and the following disclaimer in the documentation
   and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
*/

#include <dos.h>
#include <conio.h>  /* inp() and outp() */
#include <stdlib.h> /* NULL */
#include <time.h>

#include "mpu401.h"  /* include self for control */


#define MPU_DATA mpuport
#define MPU_STAT mpuport+1


/* flush everything from the MPU port (if anything) */
void mpu401_flush(int mpuport) {
  while (mpu401_poll(mpuport) != 0) inp(MPU_DATA);
}


/* wait until it's okay for us to write to the MPU */
void mpu401_waitwrite(int mpuport) {
  int buff;
  for (;;) {
    mpu401_flush(mpuport); /* make sure to flush first, in case the MPU */
    buff = inp(MPU_STAT);  /* tries to talk to us */
    if ((buff & 0x40) == 0) break;
  }
}


/* wait until it's okay for us to write to the MPU - but no longer than
 * timeout seconds. returns 0 on success, non-zero otherwise. */
static int mpu401_waitwrite_timeout(int mpuport, int timeout) {
  int buff;
  time_t notafter;
  notafter = time(NULL) + timeout;
  for (;;) {
    buff = inp(MPU_STAT);
    if ((buff & 0x40) == 0) return(0);
    if (time(NULL) >= notafter) return(-1);
  }
}


/* polls the midi interface - returns 0 if nothing is available to be read, non-zero otherwise.
   note that this should be checked as often as possible - whenever UART have some bytes for you, you MUST read them out */
int mpu401_poll(int mpuport) {
  int buff;
  buff = inp(MPU_STAT);
  if ((buff & 0x80) == 0) return(1);
  return(0);
}


void mpu401_waitread(int mpuport) {
  while (mpu401_poll(mpuport) == 0);
}


/* resets the MPU-401. returns 0 on success, non-zero otherwise. */
int mpu401_rst(int mpuport) {
  time_t timeout;
  if (mpu401_waitwrite_timeout(mpuport, 2) != 0) return(-1);  /* wait for the MPU to accept bytes from us */
  outp(MPU_STAT, 0xFF); /* Send MPU-401 RESET Command */
  /* note that some cards do not ACK on 0xFF ! that's why I should wait for a timeout here, and skip waiting if no answer after 1 or 2s */
  /* puts("wait ack"); */
  timeout = time(NULL) + 2; /* timeout is 1-2s */
  while (time(NULL) < timeout) {
    /* wait for the MPU to hand a byte to us (we are waiting for an ACK) */
    if (mpu401_poll(mpuport) != 0) {
      if (inp(MPU_DATA) == 0xFE) break; /* if we got the ACK, continue */
    }
  }
  mpu401_flush(mpuport);
  return(0);
}

void mpu401_uart(int mpuport) {
  mpu401_waitwrite(mpuport); /* Wait for port ready */
  outp(MPU_STAT, 0x3F);      /* Set MPU-401 "Dumb UART" Mode */
  /* I don't read anything back here, because MPU is not supposed to acknowledge the UART command */
}