source: avrstuff/grip2hid/main.cpp@ 5b8020c

#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/wdt.h>
#include <avr/pgmspace.h>
#include <util/delay.h>

#include <string.h>
#include <stdbool.h>

#include "../libs/usart/usart.h"

#define GRIP_PORT PORTB
#define GRIP_DDR  DDRB
#define GRIP_PIN  PINB
#define GRIP_DAT_A  (1 << 0)
#define GRIP_CLK_A  (1 << 1)
#define GRIP_DAT_B  (1 << 3)
#define GRIP_CLK_B  (1 << 2)

class GrIP
{
public:
        GrIP()
        {
                word = 0;
                count = 0;
                state = 0;
        }

        bool PushBit(uint32_t bit)
        {
                word = (word << 1) | (bit & 1);
                count++;

                switch (state) {
                        case 0:
                                if ((word & 0x3F) != 0x1F) return false;
                                count = 6;
                                state = 1;
                                break;
                        case 1:
                                if (count == 24) {
                                        state = 0;
                                        count = 0;
                                        return true;
                                }
                                break;
                }

                return false;
        }

        void Dump() {
                USARTWriteHex(word >> 16);
                USARTWriteHex(word >> 8);
                USARTWriteHex(word);
        }

private:
        uint32_t word;
        uint8_t count;
        uint8_t state;
};


int main() {
        GrIP pad[2];

        wdt_enable(WDTO_2S);

        // debug LEDs - output
        DDRD |= 0x7C;
        PORTD = 0;

        // GrIP input
        GRIP_PORT = 0; // Disable pull-ups
        GRIP_DDR = 0;  // Port as input
        uint8_t oldv = GRIP_PIN;

        USARTInit();
        USARTWriteChar('h');
        USARTWriteChar('\r');
        USARTWriteChar('\n');


        for (;;) {
                // Because the CPU is too slow, if we try to scan all pads at once we
                // don't manage to decode them (missed transitions). So we scan them
                // one at a time.
                // To scan all 4 gamepads this will take about 4 milliseconds, which
                // is not the best we could do, but is okay. When we have the real
                // hardware (with the CPU running at full 16MHz speed instead of crappy
                // 1MHz here), we can try to interleave them again (one just has to put
                // them all into a single for loop instead of separate loops for each).
                // Then we get to 1ms to scan all 4 pads in parallel, cool! And it
                // also fixes the problem mentionned below that when less pads are
                // connected, it will not slowdown waiting for one of them to timeout.

                // FIXME the loop to 255 here to wait for a bit isn't too nice. We
                // should rather use a timer with a known period?
                // Process pad1
                uint8_t i;
                for (i = 0; i < 255; i++) {
                        wdt_reset();

                        uint8_t newv = GRIP_PIN;

                        if (!(newv & GRIP_CLK_A)) { // clock is down
                                if (oldv & GRIP_CLK_A) { // and it was up at previous read
                                        // Read bit
                                        uint32_t bit = (newv & GRIP_DAT_A) != 0;
                                        i = 0;
                                        if (pad[0].PushBit(bit)) {
                                                pad[0].Dump();
                                                USARTWriteChar(' ');
                                                break;
                                        }
                                }
                        }
                        oldv = newv;
                }

                // Process pad 2
                for (i = 0; i < 255; i++) {
                        wdt_reset();

                        uint8_t newv = GRIP_PIN;
                        if (!(newv & GRIP_CLK_B)) { // clock is down
                                if (oldv & GRIP_CLK_B) { // and it was up at previous read
                                        // Read bit
                                        uint32_t bit = (newv & GRIP_DAT_B) != 0;
                                        i = 0;
                                        if (pad[1].PushBit(bit)) {
                                                pad[1].Dump();
                                                USARTWriteChar(' ');
                                                break;
                                        }
                                }
                        }
                        oldv = newv;
                }
                USARTWriteChar('\r');
                USARTWriteChar('\n');
        }

        return 0;
}