keybrd/src/Scanner_ShiftRegsReadStrobed.cpp

#include "Scanner_ShiftRegsReadStrobed.h"

Scanner_ShiftRegsReadStrobed::Scanner_ShiftRegsReadStrobed(const bool activeState,
        const uint8_t slaveSelect, const uint8_t byte_count)
    : activeState(activeState),
      slaveSelect(slaveSelect), byte_count(byte_count)
{
    pinMode(slaveSelect, OUTPUT);
    SPI.begin();
}

/* init() is called once for each row from Row constructor.
Configures controller to communicate with shift register matrix.

slaveSelect initialize not needed, only affects first scan, which is before USB is detected by OS.
    digitalWrite(slaveSelect, HIGH);
*/
void Scanner_ShiftRegsReadStrobed::init(const uint8_t strobePin)
{
    pinMode(strobePin, OUTPUT);
}

/* scan() strobes the row's strobePin and returns state of the shift register's input pins.
strobePin is Arduino pin number connected to this row.
Bit patterns are 1 bit per key.

Scanner_ShiftRegsReadStrobed class was tested on two sets of 74HC165 shift registers
and 74AHC1G126 tri-state buffer chips

74HC165 is not an SPI device.
The 74HC165 SH/LD polarity is the inverse of SPI slave-select convention.
Most SPI chips will high-Z their MISO pin when their slave select signal is high.
To use SPI-like protocol, 74HC*126 will high-Z the MISO pin when the slave select signal is low.

SPI.beginTransaction() and SPI.endTransaction() are not needed,
but would be needed if trackball uses interrupts.
*/
read_pins_t Scanner_ShiftRegsReadStrobed::scan(const uint8_t strobePin)
{
    read_pins_t readState = 0;                  //bits, 1 means key is pressed, 0 means released

//strobe off here NOT release continuously
    digitalWrite(strobePin, activeState);       //strobe on

    //SPI.beginTransaction( SPISettings(5000000, MSBFIRST, SPI_MODE0) ); //control SPI bus, 5 MHz

                                                //photo-transistor at 3.3v needs 20 ms to stabilize
    delayMicroseconds(20);                      //monitor trackball here

    digitalWrite(slaveSelect, HIGH);            //shift the data toward a serial output

    digitalWrite(strobePin, !activeState);      //strobe off to preserve IR LED life

    SPI.transfer(&readState, byte_count);

    //SPI.endTransaction();

    digitalWrite(slaveSelect, LOW);             //load parallel inputs to registers

//strobe off here still releases continuously
    return readState;
}