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208 lines
6.1 KiB
208 lines
6.1 KiB
/* Copyright 2020 Dimitris Papavasiliou <dpapavas@protonmail.ch>
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <https://www.gnu.org/licenses/>.
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*/
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#include <spi_master.h>
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#include "quantum.h"
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#include "split_util.h"
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#include "transport.h"
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#include "timer.h"
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#include "lagrange.h"
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struct led_context {
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led_t led_state;
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layer_state_t layer_state;
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};
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uint8_t transceive(uint8_t b) {
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for (SPDR = b ; !(SPSR & _BV(SPIF)) ; );
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return SPDR;
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}
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/* The SPI bus, doesn't have any form of protocol built in, so when
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* the other side isn't present, any old noise on the line will appear
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* as matrix data. To avoid interpreting data as keystrokes, we do a
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* simple n-way (8-way here) handshake before each scan, where each
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* side sends a prearranged sequence of bytes. */
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bool shake_hands(bool master) {
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const uint8_t m = master ? 0xf8 : 0;
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const uint8_t a = 0xa8 ^ m, b = 0x50 ^ m;
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bool synchronized = true;
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uint8_t i;
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i = SPSR;
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i = SPDR;
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do {
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/* Cycling the SS pin on each attempt is necessary, as it
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* resets the AVR's SPI core and guarantees proper
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* alignment. */
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if (master) {
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writePinLow(SPI_SS_PIN);
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}
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for (i = 0 ; i < 8 ; i += 1) {
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if (transceive(a + i) != b + i) {
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synchronized = false;
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break;
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}
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}
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if (master) {
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writePinHigh(SPI_SS_PIN);
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}
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} while (i < 8);
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return synchronized;
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}
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bool transport_master(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]) {
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const struct led_context context = {
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host_keyboard_led_state(),
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layer_state
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};
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uint8_t i;
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/* We shake hands both before and after transmitting the matrix.
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* Doing it before transmitting is necessary to ensure
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* synchronization: Due to the master-slave nature of the SPI bus,
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* the master calls the shots. If we just go ahead and start
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* clocking bits, the slave side might be otherwise engaged at
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* that moment, so we'll initially read zeros, or garbage. Then
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* when the slave gets around to transmitting its matrix, we'll
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* misinterpret the keys it sends, leading to spurious
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* keypresses. */
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/* The handshake forces the master to wait for the slave to be
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* ready to start transmitting. */
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do {
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shake_hands(true);
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/* Receive the matrix from the other side, while transmitting
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* LED and layer states. */
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spi_start(SPI_SS_PIN, 0, 0, 4);
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for (i = 0 ; i < sizeof(matrix_row_t[MATRIX_ROWS / 2]) ; i += 1) {
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spi_status_t x;
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x = spi_write(i < sizeof(struct led_context) ?
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((uint8_t *)&context)[i] : 0);
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if (x == SPI_STATUS_TIMEOUT) {
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return false;
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}
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((uint8_t *)slave_matrix)[i] = (uint8_t)x;
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}
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spi_stop();
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/* In case of errors during the transmission, e.g. if the
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* cable was disconnected and since there is no inherent
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* error-checking protocol, we would simply interpret noise as
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* data. */
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/* To avoid this, both sides shake hands after transmitting.
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* If synchronization was lost during transmission, the (first)
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* handshake will fail. In that case we go around and
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* re-transmit. */
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} while (!shake_hands(true));
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return true;
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}
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void transport_slave(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]) {
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static struct led_context context;
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struct led_context new_context;
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uint8_t i;
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/* Do the reverse of master above. Note that timing is critical,
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* so interrupts must be turned off. */
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cli();
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shake_hands(false);
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do {
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for (i = 0 ; i < sizeof(matrix_row_t[MATRIX_ROWS / 2]) ; i += 1) {
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uint8_t b;
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b = transceive(((uint8_t *)slave_matrix)[i]);
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if (i < sizeof(struct led_context)) {
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((uint8_t *)&new_context)[i] = b;
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}
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}
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} while (!shake_hands(false));
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sei();
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/* Update the layer and LED state if necessary. */
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if (!isLeftHand) {
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if (context.led_state.raw != new_context.led_state.raw) {
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context.led_state.raw = new_context.led_state.raw;
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led_update_kb(context.led_state);
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}
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if (context.layer_state != new_context.layer_state) {
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context.layer_state = new_context.layer_state;
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layer_state_set_kb(context.layer_state);
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}
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}
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}
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void transport_master_init(void) {
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/* We need to set the SS pin as output as the handshake logic
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* above depends on it and the SPI master driver won't do it
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* before we call spi_start(). */
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writePinHigh(SPI_SS_PIN);
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setPinOutput(SPI_SS_PIN);
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spi_init();
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shake_hands(true);
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}
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void transport_slave_init(void) {
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/* The datasheet isn't very clear on whether the internal pull-up
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* is selectable when the SS pin is used by the SPI slave, but
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* experimentations shows that it is, at least on the ATMega32u4.
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* We enable the pull-up to guard against the case where both
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* halves end up as slaves. In that case the SS pin would
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* otherwise be floating and free to fluctuate due to picked up
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* noise, etc. When reading low it would make both halves think
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* they're asserted making the MISO pin an output on both ends and
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* leading to potential shorts. */
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setPinInputHigh(SPI_SS_PIN);
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setPinInput(SPI_SCK_PIN);
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setPinInput(SPI_MOSI_PIN);
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setPinOutput(SPI_MISO_PIN);
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SPCR = _BV(SPE);
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shake_hands(false);
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}
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