1 files changed, 175 insertions, 0 deletions
diff --git a/keyboards/handwired/lagrange/transport.c b/keyboards/handwired/lagrange/transport.c
new file mode 100644
index 0000000000..2a567f24b9
--- /dev/null
+++ b/keyboards/handwired/lagrange/transport.c
@@ -0,0 +1,175 @@
+/* Copyright 2020 Dimitris Papavasiliou <dpapavas@protonmail.ch>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <spi_master.h>
+
+#include "quantum.h"
+#include "split_util.h"
+#include "timer.h"
+
+#include "lagrange.h"
+
+struct led_context {
+    led_t led_state;
+    layer_state_t layer_state;
+};
+
+uint8_t transceive(uint8_t b) {
+    for (SPDR = b ; !(SPSR & _BV(SPIF)) ; );
+    return SPDR;
+}
+
+/* The SPI bus, doens't have any form of protocol built in, so when
+ * the other side isn't present, any old noise on the line will appear
+ * as matrix data.  To avoid interpreting data as keystrokes, we do a
+ * simple n-way (8-way here) handshake before each scan, where each
+ * side sends a prearranged sequence of bytes. */
+
+void shake_hands(bool master) {
+    const uint8_t m = master ? 0xf8 : 0;
+    const uint8_t a = 0xa8 ^ m, b = 0x50 ^ m;
+
+    uint8_t i;
+
+    i = SPSR;
+    i = SPDR;
+
+    do {
+        /* Cylcling the SS pin on each attempt is necessary, as it
+         * resets the AVR's SPI core and guarantees proper
+         * alignment. */
+
+        if (master) {
+            writePinLow(SPI_SS_PIN);
+        }
+
+        for (i = 0 ; i < 8 ; i += 1) {
+            if (transceive(a + i) != b + i) {
+                break;
+            }
+        }
+
+        if (master) {
+            writePinHigh(SPI_SS_PIN);
+        }
+    } while (i < 8);
+}
+
+bool transport_master(matrix_row_t matrix[]) {
+    const struct led_context context = {
+        host_keyboard_led_state(),
+        layer_state
+    };
+
+    uint8_t i;
+
+    /* Shake hands and then receive the matrix from the other side,
+     * while transmitting LED and layer states. */
+
+    shake_hands(true);
+
+    spi_start(SPI_SS_PIN, 0, 0, 4);
+
+    for (i = 0 ; i < sizeof(matrix_row_t[MATRIX_ROWS / 2]) ; i += 1) {
+        spi_status_t x;
+
+        x = spi_write(i < sizeof(struct led_context) ?
+                      ((uint8_t *)&context)[i] : 0);
+
+        if (x == SPI_STATUS_TIMEOUT) {
+            return false;
+        }
+
+        ((uint8_t *)matrix)[i] = (uint8_t)x;
+    }
+
+    spi_stop();
+
+    return true;
+}
+
+void transport_slave(matrix_row_t matrix[]) {
+    static struct led_context context;
+    struct led_context new_context;
+
+    uint8_t i;
+
+    /* Do the reverse of master above.  Note that timing is critical,
+     * so interrupts must be turned off. */
+
+    cli();
+    shake_hands(false);
+
+    for (i = 0 ; i < sizeof(matrix_row_t[MATRIX_ROWS / 2]) ; i += 1) {
+        uint8_t b;
+
+        b = transceive(((uint8_t *)matrix)[i]);
+
+        if (i < sizeof(struct led_context)) {
+            ((uint8_t *)&new_context)[i] = b;
+        }
+    }
+
+    sei();
+
+    /* Update the layer and LED state if necessary. */
+
+    if (!isLeftHand) {
+        if (context.led_state.raw != new_context.led_state.raw) {
+            context.led_state.raw = new_context.led_state.raw;
+            led_update_kb(context.led_state);
+        }
+
+        if (context.layer_state != new_context.layer_state) {
+            context.layer_state = new_context.layer_state;
+            layer_state_set_kb(context.layer_state);
+        }
+    }
+}
+
+void transport_master_init(void) {
+    /* We need to set the SS pin as output as the handshake logic
+     * above depends on it and the SPI master driver won't do it
+     * before we call spi_start(). */
+
+    writePinHigh(SPI_SS_PIN);
+    setPinOutput(SPI_SS_PIN);
+
+    spi_init();
+
+    shake_hands(true);
+}
+
+void transport_slave_init(void) {
+    /* The datasheet isn't very clear on whether the internal pull-up
+     * is selectable when the SS pin is used by the SPI slave, but
+     * experimentations shows that it is, at least on the ATMega32u4.
+     * We enable the pull-up to guard against the case where both
+     * halves end up as slaves.  In that case the SS pin would
+     * otherwise be floating and free to fluctuate due to picked up
+     * noise, etc. When reading low it would make both halves think
+     * they're asserted making the MISO pin an output on both ends and
+     * leading to potential shorts. */
+
+    setPinInputHigh(SPI_SS_PIN);
+    setPinInput(SPI_SCK_PIN);
+    setPinInput(SPI_MOSI_PIN);
+    setPinOutput(SPI_MISO_PIN);
+
+    SPCR = _BV(SPE);
+
+    shake_hands(false);
+}