From 2d03684b6d93a80d7f168bfe85ec820df8597f02 Mon Sep 17 00:00:00 2001
From: Gregor Riepl <onitake@gmail.com>
Date: Thu, 11 Mar 2021 12:47:38 +0100
Subject: [PATCH] Added separate display firmware driver

---
 display/firmware/display.c | 108 +++++++++++++++++++++++++++++++++++++
 display/firmware/display.h |  11 ++++
 2 files changed, 119 insertions(+)
 create mode 100644 display/firmware/display.c
 create mode 100644 display/firmware/display.h

diff --git a/display/firmware/display.c b/display/firmware/display.c
new file mode 100644
index 0000000..2b5f529
--- /dev/null
+++ b/display/firmware/display.c
@@ -0,0 +1,108 @@
+#include <avr/io.h>
+#include <util/delay.h>
+#include "display.h"
+
+void display_init() {
+	// PC5, PC6, PC7: output (VFD RS, RW, E), RS=0, RW=1, E=1
+	// PD: output (VFD DB) - can be switched to input (pullup not needed)
+	PORTC |= _BV(PC6) | _BV(PC7);
+	DDRC |= _BV(PC5) | _BV(PC6) | _BV(PC7);
+	PORTD = 0x00;
+	DDRD = 0xff;
+}
+
+uint8_t display_read_ir() {
+	// switch PD to input
+	DDRD = 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);
+	uint8_t data = PIND;
+	_delay_us(0.23 - 0.16);
+	// E=0 (enable/clock)
+	PORTC &= ~_BV(PC7);
+	_delay_us(0.01);
+	// reset to idle
+	PORTC = _BV(PC6) | _BV(PC7);
+	DDRD = 0xff;
+	return data;
+}
+
+uint8_t display_read_dr() {
+	// switch PD to input
+	DDRD = 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);
+	uint8_t data = PIND;
+	_delay_us(0.23 - 0.16);
+	// E=0 (enable/clock)
+	PORTC &= ~_BV(PC7);
+	_delay_us(0.01);
+	// reset to idle
+	PORTC = _BV(PC6) | _BV(PC7);
+	DDRD = 0xff;
+	return data;
+}
+
+void display_write_ir(uint8_t data) {
+	// E=0 (enable/clock) RS=0 (IR) RW=0 (write)
+	PORTC &= ~(_BV(PC5) | _BV(PC6) | _BV(PC7));
+	_delay_us(0.23);
+	// E=1 (enable/clock)
+	PORTC |= _BV(PC7);
+	// data
+	PORTD = data;
+	_delay_us(0.23);
+	// E=0 (enable/clock)
+	PORTC &= ~_BV(PC7);
+	_delay_us(0.01);
+	// reset to idle
+	PORTC = _BV(PC6) | _BV(PC7);
+	PORTD = 0x00;
+}
+
+void display_write_dr(uint8_t data) {
+	// E=0 (enable/clock) RS=1 (IR) RW=0 (write)
+	PORTC = (PORTC & ~(_BV(PC6) | _BV(PC7))) | _BV(PC5);
+	_delay_us(0.23);
+	// E=1 (enable/clock)
+	PORTC |= _BV(PC7);
+	// data
+	PORTD = data;
+	_delay_us(0.23);
+	// E=0 (enable/clock)
+	PORTC &= ~_BV(PC7);
+	_delay_us(0.01);
+	// reset to idle
+	PORTC = _BV(PC6) | _BV(PC7);
+	PORTD = 0x00;
+}
+
+
+bool display_wait_ready() {
+	// 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 < 100; 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]);
+		}
+	}
+}
diff --git a/display/firmware/display.h b/display/firmware/display.h
new file mode 100644
index 0000000..2169890
--- /dev/null
+++ b/display/firmware/display.h
@@ -0,0 +1,11 @@
+#include <stdint.h>
+#include <stdbool.h>
+
+void display_init();
+void display_write(uint8_t command, const uint8_t *data, uint8_t length);
+
+uint8_t display_read_ir();
+uint8_t display_read_dr();
+void display_write_ir(uint8_t data);
+void display_write_dr(uint8_t data);
+bool display_wait_ready();