ps2_usart.c

/*
Copyright 2010,2011,2012,2013 Jun WAKO <wakojun@gmail.com>

This software is licensed with a Modified BSD License.
All of this is supposed to be Free Software, Open Source, DFSG-free,
GPL-compatible, and OK to use in both free and proprietary applications.
Additions and corrections to this file are welcome.


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

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

* 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.

* Neither the name of the copyright holders nor the names of
  contributors may be used to endorse or promote products derived
  from this software without specific prior written permission.

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 OWNER 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.
*/

/*
 * PS/2 protocol USART version
 */

#include <stdbool.h>
#include <avr/interrupt.h>
#include <util/delay.h>
#include "ps2.h"
#include "ps2_io.h"
#include "print.h"


#define WAIT(stat, us, err) do { \
    if (!wait_##stat(us)) { \
        ps2_error = err; \
        goto ERROR; \
    } \
} while (0)


uint8_t ps2_error = PS2_ERR_NONE;


static inline uint8_t pbuf_dequeue(void);
static inline void pbuf_enqueue(uint8_t data);
static inline bool pbuf_has_data(void);
static inline void pbuf_clear(void);


void ps2_host_init(void)
{
    idle(); // without this many USART errors occur when cable is disconnected
    PS2_USART_INIT();
    PS2_USART_RX_INT_ON();
    // POR(150-2000ms) plus BAT(300-500ms) may take 2.5sec([3]p.20)
    //_delay_ms(2500);
}

uint8_t ps2_host_send(uint8_t data)
{
    bool parity = true;
    ps2_error = PS2_ERR_NONE;

    PS2_USART_OFF();

    /* terminate a transmission if we have */
    inhibit();
    _delay_us(100); // [4]p.13

    /* 'Request to Send' and Start bit */
    data_lo();
    clock_hi();
    WAIT(clock_lo, 10000, 10);   // 10ms [5]p.50

    /* Data bit[2-9] */
    for (uint8_t i = 0; i < 8; i++) {
        _delay_us(15);
        if (data&(1<<i)) {
            parity = !parity;
            data_hi();
        } else {
            data_lo();
        }
        WAIT(clock_hi, 50, 2);
        WAIT(clock_lo, 50, 3);
    }

    /* Parity bit */
    _delay_us(15);
    if (parity) { data_hi(); } else { data_lo(); }
    WAIT(clock_hi, 50, 4);
    WAIT(clock_lo, 50, 5);

    /* Stop bit */
    _delay_us(15);
    data_hi();

    /* Ack */
    WAIT(data_lo, 50, 6);
    WAIT(clock_lo, 50, 7);

    /* wait for idle state */
    WAIT(clock_hi, 50, 8);
    WAIT(data_hi, 50, 9);

    idle();
    PS2_USART_INIT();
    PS2_USART_RX_INT_ON();
    return ps2_host_recv_response();
ERROR:
    idle();
    PS2_USART_INIT();
    PS2_USART_RX_INT_ON();
    return 0;
}

uint8_t ps2_host_recv_response(void)
{
    // Command may take 25ms/20ms at most([5]p.46, [3]p.21)
    uint8_t retry = 25;
    while (retry-- && !pbuf_has_data()) {
        _delay_ms(1);
    }
    return pbuf_dequeue();
}

uint8_t ps2_host_recv(void)
{
    if (pbuf_has_data()) {
        ps2_error = PS2_ERR_NONE;
        return pbuf_dequeue();
    } else {
        ps2_error = PS2_ERR_NODATA;
        return 0;
    }
}

ISR(PS2_USART_RX_VECT)
{
    // TODO: request RESEND when error occurs?
    uint8_t error = PS2_USART_ERROR;    // USART error should be read before data
    uint8_t data = PS2_USART_RX_DATA;
    if (!error) {
        pbuf_enqueue(data);
    } else {
        xprintf("PS2 USART error: %02X data: %02X\n", error, data);
    }
}

/* send LED state to keyboard */
void ps2_host_set_led(uint8_t led)
{
    ps2_host_send(0xED);
    ps2_host_send(led);
}


/*--------------------------------------------------------------------
 * Ring buffer to store scan codes from keyboard
 *------------------------------------------------------------------*/
#define PBUF_SIZE 32
static uint8_t pbuf[PBUF_SIZE];
static uint8_t pbuf_head = 0;
static uint8_t pbuf_tail = 0;
static inline void pbuf_enqueue(uint8_t data)
{
    uint8_t sreg = SREG;
    cli();
    uint8_t next = (pbuf_head + 1) % PBUF_SIZE;
    if (next != pbuf_tail) {
        pbuf[pbuf_head] = data;
        pbuf_head = next;
    } else {
        print("pbuf: full\n");
    }
    SREG = sreg;
}
static inline uint8_t pbuf_dequeue(void)
{
    uint8_t val = 0;

    uint8_t sreg = SREG;
    cli();
    if (pbuf_head != pbuf_tail) {
        val = pbuf[pbuf_tail];
        pbuf_tail = (pbuf_tail + 1) % PBUF_SIZE;
    }
    SREG = sreg;

    return val;
}
static inline bool pbuf_has_data(void)
{
    uint8_t sreg = SREG;
    cli();
    bool has_data = (pbuf_head != pbuf_tail);
    SREG = sreg;
    return has_data;
}
static inline void pbuf_clear(void)
{
    uint8_t sreg = SREG;
    cli();
    pbuf_head = pbuf_tail = 0;
    SREG = sreg;
}