hhkb lift distance (devoi)

#define F_CPU 16000000
#include <avr/io.h>
#include <util/delay.h>

#define CSBAR 0 //PC0 for CS
#define SKBAR 1 //PC1 for SK
#define DIO 2   //PC2 for DIO
#define Tclk 2  // clock period 4us

//ASSUMES PORTC USED FOR ALL CSBAR, SKBAR, DIO
//REQUIRES MODIFICATION


void write16bit(uint16_t data){

    for(uint8_t i = 0; i < 16; i++){    // write out data onto DIO

        if(data & (0x8000)){    // set DIO pin to data MSB
            PORTC |= (1 << DIO);
        }else{
            PORTC &= ~(1 << DIO);
        }
        data = data << 1;   // shift MSB next in line

        PORTC |= (1 << SKBAR);  // pulse clock high
        _delay_us(Tclk);
        PORTC &= ~(1 << SKBAR); // set clock low
        _delay_us(Tclk);
    }
}

void WriteEnable(uint8_t status){   // status = 1 for write, 0 for read

    PORTC &= ~(1 << CSBAR); // enable chip

    PORTC &= ~(1 << SKBAR); // clock must start low
    _delay_us(Tclk);

    write16bit(status ? 0xA300 : 0xA000);   // 1010 0011 XXXX XXXX per datasheet is write
                                            // 1010 0000 XXXX XXXX per datasheet is read

    PORTC |= (1 << SKBAR);  // end clock high
    _delay_us(Tclk);

    PORTC |= (1 << CSBAR); // set CS off

    _delay_us(5*Tclk);  // short delay to keep CS high for a required amount of time, can likely be lessened
}

uint8_t WCRead(){   // return wiper position 0-127

    PORTC &= ~(1 << CSBAR); // enable chip

    PORTC &= ~(1 << SKBAR); // clock must start low
    _delay_us(Tclk);

    write16bit(0xAB00);     // 1010 1011 XXXX XXXX per datasheet

    DDRC &= ~(1 << DIO);    // set DIO for reading

    uint8_t buf = 0;        // output buffer
    for(uint8_t i = 0; i < 8; i++){ // read 8 bits in via DIO

        if(PINC & (1 << DIO)){ // read bit is a 1
            buf |= (1 << i);
        }

        PORTC |= (1 << SKBAR);  // set clock high
        _delay_us(Tclk);

        PORTC &= ~(1 << SKBAR); // set clock low
        _delay_us(Tclk);
    }

    DDRC |= (1 << DIO);     // set DIO for writing (rest of commands)
    PORTC |= (1 << SKBAR) | (1 << CSBAR);   // end clock high and turn chip off
    return buf;
}

uint8_t WCWrite(uint8_t step){  // write wiper, step 0 to 127

    step = (step & 0xF0) >> 4 | (step & 0x0F) << 4; // byte indicating step count is sent out LSB-first
    step = (step & 0xCC) >> 2 | (step & 0x33) << 2; // meaning it must be reversed as commands are sent MSB-first
    step = (step & 0xAA) >> 1 | (step & 0x55) << 1;

    uint16_t data_fix = step << 8;  // needs empty byte afterward

    PORTC &= ~(1 << CSBAR); // enable chip
    PORTC &= ~(1 << SKBAR); // set clock low
    _delay_us(Tclk);

    write16bit(0xA600); // send write command then empty address byte
    write16bit(data_fix); // send wiper value then empty unused byte

    PORTC |= (1 << SKBAR);  // datasheet shows two extra empty clock pulses
    _delay_us(Tclk);        // seem to be ignored, but kept just in case
    PORTC &= ~(1 << SKBAR);
    _delay_us(Tclk);
    PORTC |= (1 << SKBAR);  // end clock high
    _delay_us(Tclk);

    PORTC |= (1 << CSBAR);  // disable chip
}

int main(){

    DDRC = (1 << CSBAR) | (1 << SKBAR) | (1 << DIO);
    PORTC = (1 << CSBAR) | (1 << SKBAR);

    // example read
    uint8_t read_wiper = WCRead();  // chip starts in read-mode so this is okay
                                    // can use tmk/qmk to write value as keystrokes to screen
                                    // is good to know default value

    // example write
    WriteEnable(1);     // put chip into write mode
    _delay_us(Tclk*5);  // let settle, just in case, likely not needed
    WCWrite(0x40);      // uses example value 0x40, my "default" value was 0x27 but it likely differs per-board
    _delay_us(Tclk*5);  // let settle, likely not needed
    WriteEnable(0);     // put back in read_mode

    // here would be a good place to verify that it wrote correctly with WCRead()

}