matemat/display/firmware/display.c

#include <avr/io.h>
#include <util/delay.h>
#include "display.h"

// VFDDB0 PB0
// VFDDB1 PB1
// VFDDB2 PB2
// VFDDB3 PB3
// VFDDB4 PB4
// VFDDB5 PB5
// VFDDB6 PB6
// VFDDB7 PB7
// VFDRS  PC5
// VFDRW  PC6
// VFDE   PC7
// VFDRST (PC4)

// maximum wait time until busy should be deasserted
// bail out if it takes longer than that
// unit: 10us (roughly)
// range: 0..255
#define DISPLAY_WAIT_MAX_10US 100

void display_init() {
	// PC5, PC6, PC7: output (VFD RS, RW, E), RS=0, RW=1, E=1
	// PC4: output, active low (VFD RESET), unused in display v2
	// PB0..7: output (VFD DB) - can be switched to input (pullup not needed)
	PORTB = 0x00;
	DDRB = 0xff;
	PORTC |= _BV(PC6) | _BV(PC7);
	DDRC |= _BV(PC5) | _BV(PC6) | _BV(PC7);

	display_wait_ready();
	_delay_ms(100);
	// initialize display: 8 bit, 2 lines, 50% brightness
	display_write_ir(0x3c);
	display_wait_ready();
}

static void display_set_rs(bool on) {
	if (on) {
		PORTC |= _BV(PC5);
	} else {
		PORTC &= ~_BV(PC5);
	}
}

static void display_set_rw(bool on) {
	if (on) {
		PORTC |= _BV(PC6);
	} else {
		PORTC &= ~_BV(PC6);
	}
}

static void display_set_e(bool on) {
	if (on) {
		PORTC |= _BV(PC7);
	} else {
		PORTC &= ~_BV(PC7);
	}
}

static void display_set_reset(bool on) {
	if (on) {
		PORTC |= _BV(PC4);
	} else {
		PORTC &= ~_BV(PC4);
	}
}

static void display_set_data(uint8_t data) {
	PORTB = data;
}

static uint8_t display_get_data() {
	uint8_t data = PINB;
	return data;
}

uint8_t display_read_ir() {
	// switch PD to input
	DDRB = 0x00;
	// E=0 (enable/clock) RS=0 (IR) RW=1 (read)
	PORTC = (PORTC & ~(_BV(PC5) | _BV(PC7))) | _BV(PC6);
	_delay_us(0.23);
	// E=1 (enable/clock)
	PORTC |= _BV(PC7);
	_delay_us(0.16);
	// read inputs
	uint8_t data = PINB;
	_delay_us(0.23 - 0.16);
	// E=0 (enable/clock)
	PORTC &= ~_BV(PC7);
	_delay_us(0.01);
	// reset to idle / output
	PORTC = _BV(PC6) | _BV(PC7);
	DDRB = 0xff;
	return data;
}

uint8_t display_read_dr() {
	// switch PD to input
	DDRB = 0x00;
	// E=0 (enable/clock) RS=1 (IR) RW=1 (read)
	PORTC = (PORTC & ~_BV(PC7)) | (_BV(PC5) | _BV(PC6));
	_delay_us(0.23);
	// E=1 (enable/clock)
	PORTC |= _BV(PC7);
	_delay_us(0.16);
	// read inputs
	uint8_t data = PINB;
	_delay_us(0.23 - 0.16);
	// E=0 (enable/clock)
	PORTC &= ~_BV(PC7);
	_delay_us(0.01);
	// reset to idle / output
	PORTC = _BV(PC6) | _BV(PC7);
	DDRB = 0xff;
	return data;
}

void display_write_ir(uint8_t data) {
	// RS=0 (IR) RW=0 (write)
	display_set_rs(false);
	display_set_rw(false);
	_delay_us(0.23);
	// E=1 (enable/clock)
	display_set_e(true);
	// send data
	display_set_data(data);
	_delay_us(0.23);
	// E=0 (enable/clock)
	display_set_e(false);
	_delay_us(0.01);
	// reset to idle
	display_set_rs(true);
	display_set_rw(true);
	display_set_data(0);
}

void display_write_dr(uint8_t data) {
	// RS=1 (DR) RW=0 (write)
	display_set_rs(true);
	display_set_rw(false);
	_delay_us(0.23);
	// E=1 (enable/clock)
	display_set_e(true);
	// send data
	display_set_data(data);
	_delay_us(0.23);
	// E=0 (enable/clock)
	display_set_e(false);
	_delay_us(0.01);
	// reset to idle
	display_set_rw(true);
	display_set_data(0);
}


bool display_wait_ready() {
	// FIXME hack to avoid read mode
	_delay_ms(1);
	return true;
	// FIXME

	// if the busy flag never goes high, we'll run into a deadlock here.
	// let's put a deadline on the wait loop.
	for (uint8_t i = 0; i < DISPLAY_WAIT_MAX_10US; i++) {
		// read_ir() takes about 500ns
		if (display_read_ir() & _BV(7)) return true;
		// wait 10us until the next status read
		_delay_us(10 - 0.5);
	}
	return false;
}

void display_write(uint8_t command, const uint8_t *data, uint8_t length) {
	if (display_wait_ready()) {
		display_write_ir(command);
		for (uint8_t i = 0; i < length; i++) {
			display_write_dr(data[i]);
		}
	}
}