Dump EPROM over serial with AVR

avr_eprom_dump_over_serial.c

/**
 * Thrown together program to dump 512 kbit EPROMs from an AVR ATMega64A/128A
 * More specifically, a bunch of ST M27C512 from the early 90's
 *
 * Connections:
 *
 *   Port A 0-7: low address byte (output)
 *   Port B 0-7: high address byte (output)
 *   Port D 0-7: data (input)
 *
 * Written for this expedition:
 * https://twitter.com/stecman/status/1019167609051213824
 */

#include <avr/interrupt.h>
#include <avr/io.h>
#include <util/delay.h>

void init_usart(void)
{
    cli();

    // Set baud rate to 38400 (with 16MHz clock)
    UBRR0H = (uint8_t)(25 >> 8);
    UBRR0L = (uint8_t)(25);

    // Enable receiver and transmitter
    UCSR0B = _BV(RXEN0) | _BV(TXEN0);

    // Set frame format: 8 data, 1 stop bit
    UCSR0C = (3<<UCSZ00);
    UCSR0C &= ~(1<<USBS0);

    sei();
}

void usart_transmit(uint8_t data)
{
    // Wait for empty transmit buffer
    while ( !( UCSR0A & (1<<UDRE0)) );

    // Put data into buffer, sends the data
    UDR0 = data;
}

uint8_t usart_receive(void)
{
    // Wait for data to be received
    while ( !(UCSR0A & (1<<RXC0)) );

    // Get and return received data from buffer
    return UDR0;
}

int main(void)
{
    init_usart();

    // Port A: low address byte output (start at 0x0)
    DDRA = 0xFF;
    PORTA = 0x0;

    // Port B: high address byte output (start at 0x0)
    DDRB = 0xFF;
    PORTB = 0x0;

    // Port D: data input with no pull-up
    DDRD = 0x0;
    PORTD = 0x0;

    // Wait half a second for humans
    _delay_ms(500);

    for (uint16_t address = 0; address < 0xFFFF; ++address) {

        // Set address
        PORTA = address & 0xFF;
        PORTB = address >> 8;

        // Wait 10x longer than necessary for the output to stablise (because why not)
        _delay_us(1);

        // Read and send data over serial
        usart_transmit( PIND );
    }

    return 0;
}