qmk-firmware/tmk_core/protocol/ibm4704.c

/*
Copyright 2010,2011,2012,2013 Jun WAKO <wakojun@gmail.com>
*/
#include <stdbool.h>
#include <util/delay.h>
#include "debug.h"
#include "ring_buffer.h"
#include "ibm4704.h"

#define WAIT(stat, us, err)      \
    do {                         \
        if (!wait_##stat(us)) {  \
            ibm4704_error = err; \
            goto ERROR;          \
        }                        \
    } while (0)

uint8_t ibm4704_error = 0;

void ibm4704_init(void) {
    inhibit();  // keep keyboard from sending
    IBM4704_INT_INIT();
    IBM4704_INT_ON();
    idle();  // allow keyboard sending
}

/*
Host to Keyboard
----------------
Data bits are LSB first and Parity is odd. Clock has around 60us high and 30us low part.

        ____        __   __   __   __   __   __   __   __   __   ________
Clock       \______/  \_/  \_/  \_/  \_/  \_/  \_/  \_/  \_/  \_/
            ^   ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ___
Data    ____|__/    X____X____X____X____X____X____X____X____X____X   \___
            |  Start   0    1    2    3    4    5    6    7    P   Stop
            Request by host

Start bit:  can be long as 300-350us.
Request:    Host pulls Clock line down to request to send a command.
Timing:     After Request keyboard pull up Data and down Clock line to low for start bit.
            After request host release Clock line once Data line becomes hi.
            Host writes a bit while Clock is hi and Keyboard reads while low.
Stop bit:   Host releases or pulls up Data line to hi after 9th clock and waits for keyboard pull down the line to lo.
*/
uint8_t ibm4704_send(uint8_t data) {
    bool parity   = true;  // odd parity
    ibm4704_error = 0;

    IBM4704_INT_OFF();

    /* Request to send */
    idle();
    clock_lo();

    /* wait for Start bit(Clock:lo/Data:hi) */
    WAIT(data_hi, 300, 0x30);

    /* Data bit */
    for (uint8_t i = 0; i < 8; i++) {
        WAIT(clock_hi, 100, 0x40 + i);
        if (data & (1 << i)) {
            parity = !parity;
            data_hi();
        } else {
            data_lo();
        }
        WAIT(clock_lo, 100, 0x48 + i);
    }

    /* Parity bit */
    WAIT(clock_hi, 100, 0x34);
    if (parity) {
        data_hi();
    } else {
        data_lo();
    }
    WAIT(clock_lo, 100, 0x35);

    /* Stop bit */
    WAIT(clock_hi, 100, 0x34);
    data_hi();

    /* End */
    WAIT(data_lo, 100, 0x36);

    idle();
    IBM4704_INT_ON();
    return 0;
ERROR:
    idle();
    if (ibm4704_error > 0x30) {
        xprintf("S:%02X ", ibm4704_error);
    }
    IBM4704_INT_ON();
    return -1;
}

/* wait forever to receive data */
uint8_t ibm4704_recv_response(void) {
    while (!rbuf_has_data()) {
        _delay_ms(1);
    }
    return rbuf_dequeue();
}

uint8_t ibm4704_recv(void) {
    if (rbuf_has_data()) {
        return rbuf_dequeue();
    } else {
        return -1;
    }
}

/*
Keyboard to Host
----------------
Data bits are LSB first and Parity is odd. Clock has around 60us high and 30us low part.

        ____       __   __   __   __   __   __   __   __   __   _______
Clock       \_____/  \_/  \_/  \_/  \_/  \_/  \_/  \_/  \_/  \_/
             ____ ____ ____ ____ ____ ____ ____ ____ ____ ____
Data    ____/    X____X____X____X____X____X____X____X____X____X________
            Start   0    1    2    3    4    5    6    7    P  Stop

Start bit:  can be long as 300-350us.
Inhibit:    Pull Data line down to inhibit keyboard to send.
Timing:     Host reads bit while Clock is hi.(rising edge)
Stop bit:   Keyboard pulls down Data line to lo after 9th clock.
*/
ISR(IBM4704_INT_VECT) {
    static enum { BIT0, BIT1, BIT2, BIT3, BIT4, BIT5, BIT6, BIT7, PARITY, STOP } state = BIT0;
    // LSB first
    static uint8_t data = 0;
    // Odd parity
    static uint8_t parity = false;

    ibm4704_error = 0;

    switch (state) {
        case BIT0:
        case BIT1:
        case BIT2:
        case BIT3:
        case BIT4:
        case BIT5:
        case BIT6:
        case BIT7:
            data >>= 1;
            if (data_in()) {
                data |= 0x80;
                parity = !parity;
            }
            break;
        case PARITY:
            if (data_in()) {
                parity = !parity;
            }
            if (!parity) goto ERROR;
            break;
        case STOP:
            // Data:Low
            WAIT(data_lo, 100, state);
            rbuf_enqueue(data);
            ibm4704_error = IBM4704_ERR_NONE;
            goto DONE;
            break;
        default:
            goto ERROR;
    }
    state++;
    goto RETURN;
ERROR:
    ibm4704_error = state;
    while (ibm4704_send(0xFE)) _delay_ms(1);  // resend
    xprintf("R:%02X%02X\n", state, data);
DONE:
    state  = BIT0;
    data   = 0;
    parity = false;
RETURN:
    return;
}