Using SPI with 74HC595 and TPIC6B595

Using Arduino LEDs and Multiplexing
4

Thanks for the answer. It makes sense (afterwards!).

If the multiplexing can be fast enough without SPI, I would prefer not to use SPI. So I'm posting here my code and you can tell me if something makes it slow.

I represent a "picture" on my 8x8 matrix by a uint64_t. When a bit is high in int, so should be the corresponding LED.

First we loop on each bit:

void pic_display(pic_t pic)
{
    int line;
    int column;
    
    for(int i = 0; i < 64; i++) {
        line = i / 8;
        column = i % 8;

        if(pic & (0x8000000000000000 >> i)) {
            matrix_display_dot(line, column);
        }
    }
}

And then we call matrix_display_dot:

void matrix_display_dot(char line, char column)
{
    // set RCLK low; wait till we transmit the byte, and they moving it high will output the data
    digitalWrite(RCLKPin, LOW);
    digitalWrite(RCKPin_tpic6b595, LOW);
    
    // shift out the bits (MSBFIRST = most significant bit first)
    shiftOut(SERPin, SRCLKPin, MSBFIRST, 1 << line);
    shiftOut(SERPin_tpic6b595, SRCKPin_tpic6b595, MSBFIRST, 1 << column);
    
    // send shift register data to the storage register
    digitalWrite(RCLKPin, HIGH);
    digitalWrite(RCKPin_tpic6b595, HIGH);
}

Can this be made fast enough to have persistence of vision? For now it's just flickering.

P.S: I know I can mix C++ but I'm using a makefile without the Arduino IDE and would prefer to have it in plain C since I don't thing C++ is relevant for such small projects, I don't like C++ that much and I'm considering to learn the AVR behind Arduino in the long term.