Extensible split data sync (#11930)

* Extensible split data sync capability through transactions.

- Split common transport has been split up between the transport layer
  and data layer.
- Split "transactions" model used, with convergence between I2C and
  serial data definitions.
- Slave matrix "generation count" is used to determine if the full slave
  matrix needs to be retrieved.
- Encoders get the same "generation count" treatment.
- All other blocks of data are synchronised when a change is detected.
- All transmissions have a globally-configurable deadline before a
  transmission is forced (`FORCED_SYNC_THROTTLE_MS`, default 100ms).
- Added atomicity for all core-synced data, preventing partial updates
- Added retries to AVR i2c_master's i2c_start, to minimise the number of
  failed transactions when interrupts are disabled on the slave due to
  atomicity checks.
- Some keyboards have had slight modifications made in order to ensure
  that they still build due to firmware size restrictions.

* Fixup LED_MATRIX compile.

* Parameterise ERROR_DISCONNECT_COUNT.

1 files changed, 18 insertions, 1 deletions

diff --git a/drivers/avr/i2c_master.c b/drivers/avr/i2c_master.c
index b1e4885298..2773e00778 100644
--- a/drivers/avr/i2c_master.c
+++ b/drivers/avr/i2c_master.c
@@ -28,8 +28,14 @@
 #    define F_SCL 400000UL  // SCL frequency
 #endif
 
+#ifndef I2C_START_RETRY_COUNT
+#    define I2C_START_RETRY_COUNT 20
+#endif  // I2C_START_RETRY_COUNT
+
 #define TWBR_val (((F_CPU / F_SCL) - 16) / 2)
 
+#define MAX(X, Y) ((X) > (Y) ? (X) : (Y))
+
 void i2c_init(void) {
     TWSR = 0; /* no prescaler */
     TWBR = (uint8_t)TWBR_val;
@@ -47,7 +53,7 @@ void i2c_init(void) {
 #endif
 }
 
-i2c_status_t i2c_start(uint8_t address, uint16_t timeout) {
+static i2c_status_t i2c_start_impl(uint8_t address, uint16_t timeout) {
     // reset TWI control register
     TWCR = 0;
     // transmit START condition
@@ -86,6 +92,17 @@ i2c_status_t i2c_start(uint8_t address, uint16_t timeout) {
     return I2C_STATUS_SUCCESS;
 }
 
+i2c_status_t i2c_start(uint8_t address, uint16_t timeout) {
+    // Retry i2c_start_impl a bunch times in case the remote side has interrupts disabled.
+    uint16_t     timeout_timer = timer_read();
+    uint16_t     time_slice    = MAX(1, (timeout == (I2C_TIMEOUT_INFINITE)) ? 5 : (timeout / (I2C_START_RETRY_COUNT)));  // if it's infinite, wait 1ms between attempts, otherwise split up the entire timeout into the number of retries
+    i2c_status_t status;
+    do {
+        status = i2c_start_impl(address, time_slice);
+    } while ((status < 0) && ((timeout == I2C_TIMEOUT_INFINITE) || (timer_elapsed(timeout_timer) < timeout)));
+    return status;
+}
+
 i2c_status_t i2c_write(uint8_t data, uint16_t timeout) {
     // load data into data register
     TWDR = data;