Low level function to read/write EEPROM on avr328p 8-bits microcontroler

eeprom.rs

// author: @FlavioVilante
// MIT License - Copyright 2022 

use ruduino::prelude::without_interrupts;

use crate::microcontroler::register:: {
    write_register,
    read_register,
};

use crate::common:: {
    word_to_byte,
    get_bit_at,
};

//EEPROM registers addresses and bits
const EEARH: *mut u8 = 0x42 as *mut u8;
const EEARL: *mut u8 = 0x41 as *mut u8;
const EECR: *mut u8 = 0x3F as *mut u8;
const EEDR: *mut u8 = 0x40 as *mut u8;
const EEPE: u8 =  0b0000010;
const EEMPE: u8 = 0b0000100;
const EERE: u8 =  0b0000001;

// normalize is to clamp the 16 bits address to a 9 bits address (1+8)
fn normalize_eeprom_address(address: u16) -> (u8, u8) {
    let (address_low, address_high) = word_to_byte(address);
    let bit9 = get_bit_at(address_high, 0); // only bit 9 of address16 are used, other bits are reserved by the microcontroller hardware
    (bit9, address_low)
}

pub fn read_eeprom(address: u16) -> u8 {
    let (bit9, address_low) = normalize_eeprom_address(address);
    // set EEPROM address register
    write_register(EEARH, bit9);
    write_register(EEARL, address_low); 
    //do read
    while (read_register(EECR) & (1<<EEPE)) == 1 { }; // wait until EEPE become to zero by hardware
    write_register(EECR, read_register(EECR) | (1<<EERE));
    read_register(EEDR)
}

pub fn write_eeprom(address: u16, data: u8) -> () {
    // set EEPROM address and data register
    let (bit9, address_low) = normalize_eeprom_address(address);
    write_register(EEARH, bit9);
    write_register(EEARL, address_low);
    write_register(EEDR, data); 
    // write operation
    while (read_register(EECR) & (1<<EEPE)) == 1 { }; // wait until EEPE become to zero
    without_interrupts(|| {
        write_register(EECR, read_register(EECR) | (1<<EEMPE));
        write_register(EECR, read_register(EECR) | (1<<EEPE));
    });
}

register.rs

// low level functions to read and write values direct on microcontroler registers
// for details on what work each register perform see microcontroler datasheet
// for example: ATMEL AVR328P DATASHEET -> https://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-7810-Automotive-Microcontrollers-ATmega328P_Datasheet.pdf

pub fn write_register(reg_address: *mut u8, value: u8) -> () {
    unsafe {
        core::ptr::write_volatile(reg_address, value);
    }
}

pub fn read_register(reg_address: *const u8) -> u8 {
    unsafe {
        core::ptr::read_volatile(reg_address)
    }
}