// Utility to unlock 28C256 Software Data Protection (SDP) for the Ben Eater EEPROM
// programmer design.  This hardware is similar to the TommyPROM hardware, but it uses
// different shift register chips and different pin assignments.
//
// To meet the timing requirements of the SDP unlock, this code uses direct port writes
// to set and read values on the data bus.  It will work Arduino Uno and Nano hardware,
// but would require changes for other platforms.
#define SHIFT_DATA 2
#define SHIFT_CLK 3
#define SHIFT_LATCH 4
#define WRITE_EN 13


// 32 byte test pattern to verify the EEPROM device.  The pattern includes a walking one
// and a walking zero, which may help to detect pins that are tied together or swapped.
byte data[] = {
    'A',  'B',  'C',  'D',  'E',  'F',  'G',  'H',
    0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80,
    0x7f, 0xbf, 0xdf, 0xef, 0xf7, 0xfb, 0xfd, 0xfe,
    0x00, 0xff, 0x55, 0xaa, '0',  '1',  '2',  '3'
};

void enableWrite()      { digitalWrite(WRITE_EN, LOW);}
void disableWrite()     { digitalWrite(WRITE_EN, HIGH);}

void setup() {
    // put your setup code here, to run once:
    pinMode(SHIFT_DATA, OUTPUT);
    pinMode(SHIFT_CLK, OUTPUT);
    pinMode(SHIFT_LATCH, OUTPUT);
    disableWrite();
    pinMode(WRITE_EN, OUTPUT);
    Serial.begin(57600);

    Serial.print("\nDisabling EEPROM Software Data Protection(SDP)...");
    disableSoftwareWriteProtect();
    Serial.println(" done\n");

    // Program a test pattern and fill the remainder of the first block with 0xff
    Serial.print("Programming EEPROM...");
    for (word address = 0; (address < sizeof(data)); address++) {
        writeEEPROM(address, data[address]);
    }
    for (word address = sizeof(data); (address < 256); address++) {
        writeEEPROM(address, 0xff);
    }
    Serial.println(" done\n");

    // Read and print out the contents of the EERPROM
    Serial.println("Reading EEPROM");
    printContents();
}

void loop() {
}


// Output the address bits and outputEnable signal using shift registers.
void setAddress(int addr, bool outputEnable) {
    // Set the highest bit as the output enable bit (active low)
    if (outputEnable) {
        addr &= ~0x8000;
    } else {
        addr |= 0x8000;
    }
    byte dataMask = 0x04;
    byte clkMask = 0x08;
    byte latchMask = 0x10;

    // Make sure the clock is low to start.
    PORTD &= ~clkMask;

    // Shift 16 bits in, starting with the MSB.
    for (uint16_t ix = 0; (ix < 16); ix++)
    {
        // Set the data bit
        if (addr & 0x8000)
        {
            PORTD |= dataMask;
        }
        else
        {
            PORTD &= ~dataMask;
        }

        // Toggle the clock high then low
        PORTD |= clkMask;
        delayMicroseconds(3);
        PORTD &= ~clkMask;
        addr <<= 1;
    }

    // Latch the shift register contents into the output register.
    PORTD &= ~latchMask;
    delayMicroseconds(1);
    PORTD |= latchMask;
    delayMicroseconds(1);
    PORTD &= ~latchMask;
}



// Read a byte from the EEPROM at the specified address.
byte readEEPROM(int address) {
    setDataBusMode(INPUT);
    setAddress(address, /*outputEnable*/ true);
    return readDataBus();
}

// Write a byte to the EEPROM at the specified address.
void writeEEPROM(int address, byte data) {
    setAddress(address, /*outputEnable*/ false);
    setDataBusMode(OUTPUT);
    writeDataBus(data);
    enableWrite();
    delayMicroseconds(1);
    disableWrite();
    delay(10);
}

// Read the first 256 byte block of the EEPROM and dump it to the serial monitor.
void printContents() {
    for (int base = 0; (base < 256); base += 16) {
        byte data[16];
        for (int offset = 0; offset <= 15; offset += 1) {
            data[offset] = readEEPROM(base + offset);
        }

        char buf[80];
        sprintf(buf, "%04x:  %02x %02x %02x %02x %02x %02x %02x %02x   %02x %02x %02x %02x %02x %02x %02x %02x",
            base, data[0], data[1], data[2], data[3], data[4], data[5], data[6], data[7],
            data[8], data[9], data[10], data[11], data[12], data[13], data[14], data[15]);
        Serial.println(buf);
    }
}

// Write the special six-byte code to turn off Software Data Protection.
void disableSoftwareWriteProtect() {
    disableWrite();
    setDataBusMode(OUTPUT);

    setByte(0xaa, 0x5555);
    setByte(0x55, 0x2aaa);
    setByte(0x80, 0x5555);
    setByte(0xaa, 0x5555);
    setByte(0x55, 0x2aaa);
    setByte(0x20, 0x5555);

    setDataBusMode(INPUT);
    delay(10);
}

// Write the special three-byte code to turn on Software Data Protection.
void enableSoftwareWriteProtect() {
    disableWrite();
    setDataBusMode(OUTPUT);

    setByte(0xaa, 0x5555);
    setByte(0x55, 0x2aaa);
    setByte(0xa0, 0x5555);

    setDataBusMode(INPUT);
    delay(10);
}

// Set the I/O state of the data bus.
// The 8 bits data bus are is on pins D5..D12.
void setDataBusMode(uint8_t mode) {
    // On the Uno and Nano, D5..D12 maps to the upper 3 bits of port D and the
    // lower 5 bits of port B.
    if (mode == OUTPUT) {
        DDRB |= 0x1f;
        DDRD |= 0xe0;
    } else {
        DDRB &= 0xe0;
        DDRD &= 0x1f;
    }
}

// Read a byte from the data bus.  The caller must set the bus to input_mode
// before calling this or no useful data will be returned.
byte readDataBus() {
    return (PINB << 3) | (PIND >> 5);
}

// Write a byte to the data bus.  The caller must set the bus to output_mode
// before calling this or no data will be written.
void writeDataBus(byte data) {
     PORTB = (PORTB & 0xe0) | (data >> 3);
     PORTD = (PORTD & 0x1f) | (data << 5);
}

// Set an address and data value and toggle the write control.  This is used
// to write control sequences, like the software write protect.  This is not a
// complete byte write function because it does not set the chip enable or the
// mode of the data bus.
void setByte(byte value, word address) {
    setAddress(address, false);
    writeDataBus(value);

    delayMicroseconds(1);
    enableWrite();
    delayMicroseconds(1);
    disableWrite();
}