#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()
	
}