Import code from old repository from 2018

Old repository: https://github.com/binaryDiv/z80_computer

firmware_src/eeprom.c

@@ -0,0 +1,117 @@
+#include "config.h"
+#include "eeprom.h"
+
+#include <avr/io.h>
+#include <util/delay.h>
+#include "BitIO.h"
+
+// Initialize EEPROM
+void eepromInit() {
+	// Set initial value for control port (all disabled -- INVERTED VALUES, ~CE, ~OE, ~WE)
+	BIT_SET(&EEP_CTRL_PORT, EEP_CTRL_BIT_CE);
+	BIT_SET(&EEP_CTRL_PORT, EEP_CTRL_BIT_OE);
+	BIT_SET(&EEP_CTRL_PORT, EEP_CTRL_BIT_WE);
+
+	// Set data direction register for control port
+	EEP_CTRL_DDR |= (1 << EEP_CTRL_BIT_CE)
+	             |  (1 << EEP_CTRL_BIT_OE)
+	             |  (1 << EEP_CTRL_BIT_WE);
+
+	// Set initial value for address (0x0000)
+	EEP_ADDR_LOW_PORT  = 0x00;
+	EEP_ADDR_HIGH_PORT = 0x00;
+
+	// Set data direction register for address ports
+	EEP_ADDR_LOW_DDR  = 0xFF;
+	EEP_ADDR_HIGH_DDR = 0xFF;
+
+	// Set data direction register and initial value for IO port (initialize in reading mode)
+	EEP_DATA_PORT = 0x00;
+	EEP_DATA_DDR  = 0x00;
+}
+
+// Enable read mode (set data direction registers and enable output)
+void eepromSetReadMode() {
+	// Reset control bits (shouldn't be necessary, but let's be safe)
+	BIT_SET(&EEP_CTRL_PORT, EEP_CTRL_BIT_CE);
+	BIT_SET(&EEP_CTRL_PORT, EEP_CTRL_BIT_OE);
+	BIT_SET(&EEP_CTRL_PORT, EEP_CTRL_BIT_WE);
+
+	// Set data pins as input, reset PORT to disable pullups
+	EEP_DATA_PORT = 0x00;
+	EEP_DATA_DDR  = 0x00;
+}
+
+// Enable write mode (set data direction registers)
+void eepromSetWriteMode() {
+	// Reset control bits (shouldn't be necessary, but let's be safe)
+	BIT_SET(&EEP_CTRL_PORT, EEP_CTRL_BIT_CE);
+	BIT_SET(&EEP_CTRL_PORT, EEP_CTRL_BIT_OE);
+	BIT_SET(&EEP_CTRL_PORT, EEP_CTRL_BIT_WE);
+
+	// Set data pins as output, reset data port
+	EEP_DATA_PORT = 0x00;
+	EEP_DATA_DDR  = 0xFF;
+}
+
+// Set address
+static inline void eepromSetAddress(address_t address) {
+	// Set low and high address bytes
+	// (We actually only have 15 bit, the 16th will just be ignored)
+	EEP_ADDR_LOW_PORT  = address & 0xFF;
+	EEP_ADDR_HIGH_PORT = address >> 8;
+}
+
+// Read byte (assumes we're in read mode)
+uint8_t eepromReadByte(address_t address) {
+	// Assume we're in read mode
+
+	// Set address
+	eepromSetAddress(address);
+
+	// Latch address
+	BIT_CLEAR(&EEP_CTRL_PORT, EEP_CTRL_BIT_CE);
+	BIT_CLEAR(&EEP_CTRL_PORT, EEP_CTRL_BIT_OE);
+
+	// 1 tick = 62.5 ns, EEPROM access time is 150 ns.
+	// 2 NOPs seem to be sufficient, but let's be sure.
+	_NOP();
+	_NOP();
+	_NOP();
+
+	// Get data
+	uint8_t byte = EEP_DATA_PIN;
+
+	// Reset ~OE, ~CE
+	BIT_SET(&EEP_CTRL_PORT, EEP_CTRL_BIT_OE);
+	BIT_SET(&EEP_CTRL_PORT, EEP_CTRL_BIT_CE);
+
+	// Read and return data byte
+	return byte;
+}
+
+// Write byte (assumes we're in write mode)
+void eepromWriteByte(address_t address, uint8_t data) {
+	// Assume we're in write mode
+
+	// Set address
+	eepromSetAddress(address);
+
+	// Falling edge: latch address
+	BIT_CLEAR(&EEP_CTRL_PORT, EEP_CTRL_BIT_CE);
+	BIT_CLEAR(&EEP_CTRL_PORT, EEP_CTRL_BIT_WE);
+
+	// Set data byte
+	EEP_DATA_PORT = data;
+
+	// Data setup time (50ns)
+	_NOP();
+
+	// Rising edge: latch data, start write cycle
+	BIT_SET(&EEP_CTRL_PORT, EEP_CTRL_BIT_WE);
+	BIT_SET(&EEP_CTRL_PORT, EEP_CTRL_BIT_CE);
+
+	// Write pulse width high (50ns)
+	_NOP();
+}
+