// This controls the shift register that generates the address lines for A0..A15 for most
// chip families.
//
// Note that this uses direct port control instead of digitalWrite calls so that the code
// can run fast enough to meet the tBLC requirements for SDP and block writes.  This
// sacrifices portability and readability for speed. 
//
// This code will only work on Arduino Uno and Nano hardware.  The ports for other
// Arduinos map to different IO pins.

#include "PromAddressDriver.h"

#define ADDR_CLK_HI     A3
#define ADDR_CLK_LO     A4
#define ADDR_DATA       A5

// Define masks for the address clk and data lines on PC3..PC5 for direct port control.
#define ADDR_CLK_HI_MASK    0x08
#define ADDR_CLK_LO_MASK    0x10
#define ADDR_DATA_MASK      0x20

// When using the 74LS595 shift registers, the RCLK lines of both shift registers can be
// connected to D13 (PB5).
#define RCLK_595_MASK       0x20


void PromAddressDriver::begin()
{
    // The address control pins are always outputs.
    pinMode(ADDR_DATA, OUTPUT);
    pinMode(ADDR_CLK_LO, OUTPUT);
    pinMode(ADDR_CLK_HI, OUTPUT);
    digitalWrite(ADDR_DATA, LOW);
    digitalWrite(ADDR_CLK_LO, LOW);
    digitalWrite(ADDR_CLK_HI, LOW);
    DDRB |= RCLK_595_MASK; // Set D13 as output

    // To save time, the setAddress only writes the hi byte if it has changed.
    // The value used to detect the change is initialized to a non-zero value,
    // so set an initial address to avoid the the case where the first address
    // written is the 'magic' initial address.
    setAddress(0x0000);
}


// Set a 16 bit address in the two address shift registers.
void PromAddressDriver::setAddress(word address)
{
    static byte lastHi = 0xca;
    byte hi = address >> 8;
    byte lo = address & 0xff;

    if (hi != lastHi)
    {
        setAddressRegister(ADDR_CLK_HI, hi);
        lastHi = hi;
    }
    setAddressRegister(ADDR_CLK_LO, lo);
}

// Shift an 8-bit value into one of the address shift registers.  Note that
// the data pins are tied together, selecting the high or low address register
// is a matter of using the correct clock pin to shift the data in.
void PromAddressDriver::setAddressRegister(uint8_t clkPin, byte addr)
{
    byte mask = 0;
    if (clkPin == ADDR_CLK_HI)
        mask = ADDR_CLK_HI_MASK;
    else if (clkPin == ADDR_CLK_LO)
        mask = ADDR_CLK_LO_MASK;

    // Make sure the clock is low to start.
    PORTC &= ~mask;

    // Shift 8 bits in, starting with the MSB.
    for (int ix = 0; (ix < 8); ix++)
    {
        // Set the data bit
        if (addr & 0x80)
        {
            PORTC |= ADDR_DATA_MASK;
        }
        else
        {
            PORTC &= ~ADDR_DATA_MASK;
        }

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

    // Toggle the output latch for 74LS595 hardware.  For the default TommyPROM hardware
    // this just harmlessly writes to the D13 line that isn't connected to anything.
    PORTB &= ~RCLK_595_MASK;
    delayMicroseconds(1);
    PORTB |= RCLK_595_MASK;
    delayMicroseconds(1);
    PORTB &= ~RCLK_595_MASK;
}