| 1 | #include <avr/io.h>
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| 2 |
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| 3 | #include <stdbool.h>
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| 4 |
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| 5 | // The UART is on PD2 (Rx) and PD3 (Tx)
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| 6 | // The gamepads are all connected on port B
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| 7 | #define GRIP_PORT PORTD
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| 8 | #define GRIP_DDR DDRD
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| 9 | #define GRIP_PIN PIND
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| 10 | #define GRIP_CLK_A (1 << 0)
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| 11 | #define GRIP_DAT_A (1 << 1)
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| 12 | #define GRIP_CLK_B (1 << 2)
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| 13 | #define GRIP_DAT_B (1 << 3)
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| 14 | #define GRIP_CLK_C (1 << 4)
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| 15 | #define GRIP_DAT_C (1 << 5)
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| 16 | #define GRIP_CLK_D (1 << 6)
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| 17 | #define GRIP_DAT_D (1 << 7)
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| 18 |
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| 19 | class GrIP
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| 20 | {
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| 21 | public:
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| 22 | GrIP()
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| 23 | {
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| 24 | word = 0;
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| 25 | count = 0;
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| 26 | state = 0;
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| 27 | }
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| 28 |
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| 29 | // Push the next bit and returns true if it completes a word.
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| 30 | // The whole 24 bit word is stored in "word" and consists of:
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| 31 | // - One 7-bit sync pattern: always 0111111
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| 32 | // - Three 6-bit blocks starting with a 0 followed by 5 button bits
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| 33 | bool PushBit(uint32_t bit)
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| 34 | {
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| 35 | word = (word >> 1) | ((bit & 1) << 31);
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| 36 | count++;
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| 37 |
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| 38 | switch (state) {
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| 39 | case 0:
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| 40 | if ((word & 0xFE000000) != 0x7C000000) return false;
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| 41 | count = 7;
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| 42 | state = 1;
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| 43 | break;
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| 44 | case 1:
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| 45 | if (count == 24) {
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| 46 | state = 0;
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| 47 | count = 0;
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| 48 | return true;
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| 49 | }
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| 50 | break;
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| 51 | }
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| 52 |
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| 53 | return false;
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| 54 | }
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| 55 |
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| 56 | public:
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| 57 | uint32_t word;
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| 58 | private:
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| 59 | uint8_t count;
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| 60 | uint8_t state; // 0 = looking for sync, 1 = synchronized (we received 0111111)
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| 61 | };
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| 62 |
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| 63 |
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| 64 | extern "C" void GrIP_Init() {
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| 65 | // GrIP input
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| 66 | GRIP_PORT = 0xFF; // Enable pull-ups
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| 67 | GRIP_DDR = 0; // Port as input
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| 68 | }
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| 69 |
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| 70 | extern "C" uint8_t GrIP_Read(uint32_t* v, uint8_t k2) {
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| 71 | // Initial value of oldv for edge detection
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| 72 | uint8_t oldv = GRIP_PIN;
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| 73 | static uint8_t k = 0;
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| 74 | if (k2 != 0)
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| 75 | k = k2 - 1;
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| 76 | else {
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| 77 | k++; if (k > 3) k = 0;
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| 78 | }
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| 79 |
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| 80 | // Because the CPU is too slow, if we try to scan all pads at once we
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| 81 | // don't manage to decode them (missed transitions). So we scan them
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| 82 | // one at a time.
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| 83 | // To scan all 4 gamepads this will take about 4 milliseconds, which
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| 84 | // is not the best we could do, but is okay. When we have the real
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| 85 | // hardware (with the CPU running at full 16MHz speed instead of crappy
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| 86 | // 1MHz here), we can try to interleave them again (one just has to put
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| 87 | // them all into a single for loop instead of separate loops for each).
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| 88 | // Then we get to 1ms to scan all 4 pads in parallel, cool! And it
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| 89 | // also fixes the problem mentionned below that when less pads are
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| 90 | // connected, it will not slowdown waiting for one of them to timeout.
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| 91 | //
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| 92 | // When a gamepad is plugged, the loop seems to complete in around 1000 iterations.
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| 93 | // When no gamepad is plugged, that's a timeout.
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| 94 |
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| 95 | // Process pad1
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| 96 | GrIP pad;
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| 97 | uint16_t i;
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| 98 |
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| 99 | if (k == 0)
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| 100 | for (i = 0; i < 2048; i++) {
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| 101 | uint8_t newv = GRIP_PIN;
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| 102 | if (!(newv & GRIP_CLK_A)) { // clock is down
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| 103 | if (oldv & GRIP_CLK_A) { // and it was up at previous read
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| 104 | // Read bit
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| 105 | uint32_t bit = (newv & GRIP_DAT_A) != 0;
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| 106 | if (pad.PushBit(bit)) {
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| 107 | *v = pad.word;
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| 108 | break;
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| 109 | }
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| 110 | }
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| 111 | }
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| 112 | oldv = newv;
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| 113 | }
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| 114 |
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| 115 | // Process pad 2
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| 116 | if (k == 1)
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| 117 | for (i = 0; i < 2048; i++) {
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| 118 | uint8_t newv = GRIP_PIN;
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| 119 | if (!(newv & GRIP_CLK_B)) { // clock is down
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| 120 | if (oldv & GRIP_CLK_B) { // and it was up at previous read
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| 121 | // Read bit
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| 122 | uint32_t bit = (newv & GRIP_DAT_B) != 0;
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| 123 | if (pad.PushBit(bit)) {
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| 124 | *v = pad.word;
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| 125 | break;
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| 126 | }
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| 127 | }
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| 128 | }
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| 129 | oldv = newv;
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| 130 | }
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| 131 |
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| 132 | // Process pad 3
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| 133 | if (k == 2)
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| 134 | for (i = 0; i < 2048; i++) {
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| 135 | uint8_t newv = GRIP_PIN;
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| 136 | if (!(newv & GRIP_CLK_C)) { // clock is down
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| 137 | if (oldv & GRIP_CLK_C) { // and it was up at previous read
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| 138 | // Read bit
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| 139 | uint32_t bit = (newv & GRIP_DAT_C) != 0;
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| 140 | if (pad.PushBit(bit)) {
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| 141 | *v = pad.word;
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| 142 | break;
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| 143 | }
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| 144 | }
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| 145 | }
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| 146 | oldv = newv;
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| 147 | }
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| 148 |
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| 149 | // Process pad 4
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| 150 | if (k == 3)
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| 151 | for (i = 0; i < 2048; i++) {
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| 152 | uint8_t newv = GRIP_PIN;
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| 153 | if (!(newv & GRIP_CLK_D)) { // clock is down
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| 154 | if (oldv & GRIP_CLK_D) { // and it was up at previous read
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| 155 | // Read bit
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| 156 | uint32_t bit = (newv & GRIP_DAT_D) != 0;
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| 157 | if (pad.PushBit(bit)) {
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| 158 | *v = pad.word;
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| 159 | break;
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| 160 | }
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| 161 | }
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| 162 | }
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| 163 | oldv = newv;
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| 164 | }
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| 165 |
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| 166 | return k;
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| 167 | }
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| 168 |
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| 169 |
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