Transfer a synchronization message to make I2C recovery more robust.

left/src/slave_protocol_handler.c

@@ -65,6 +65,11 @@ void SlaveTxHandler(void)
         case SlaveCommand_RequestProperty: {
             uint8_t propertyId = RxMessage.data[1];
             switch (propertyId) {
+                case SlaveProperty_Sync: {
+                    memcpy(TxMessage.data, SlaveSyncString, SLAVE_SYNC_STRING_LENGTH);
+                    TxMessage.length = SLAVE_SYNC_STRING_LENGTH;
+                    break;
+                }
                 case SlaveProperty_Features: {
                     uhk_module_features_t *moduleFeatures = (uhk_module_features_t*)&TxMessage.data;
                     moduleFeatures->keyCount = MODULE_KEY_COUNT;

right/src/slave_drivers/uhk_module_driver.c

@@ -51,7 +51,7 @@ void UhkModuleSlaveDriver_Init(uint8_t uhkModuleDriverId)
     uhkModuleTargetVars->ledPwmBrightness = 0;
 
     uhk_module_phase_t *uhkModulePhase = &uhkModuleState->phase;
-    *uhkModulePhase = UhkModulePhase_RequestModuleFeatures;
+    *uhkModulePhase = UhkModulePhase_RequestSync;
 
     uhk_module_i2c_addresses_t *uhkModuleI2cAddresses = moduleIdsToI2cAddresses + uhkModuleDriverId;
     uhkModuleState->firmwareI2cAddress = uhkModuleI2cAddresses->firmwareI2cAddress;
@@ -70,6 +70,28 @@ status_t UhkModuleSlaveDriver_Update(uint8_t uhkModuleDriverId)
 
     switch (*uhkModulePhase) {
 
+        // Sync communication
+        case UhkModulePhase_RequestSync:
+            txMessage.data[0] = SlaveCommand_RequestProperty;
+            txMessage.data[1] = SlaveProperty_Sync;
+            txMessage.length = 2;
+            status = tx(i2cAddress);
+            *uhkModulePhase = UhkModulePhase_ReceiveSync;
+            break;
+        case UhkModulePhase_ReceiveSync:
+            status = rx(rxMessage, i2cAddress);
+            *uhkModulePhase = UhkModulePhase_ProcessSync;
+            break;
+        case UhkModulePhase_ProcessSync: {
+            bool isMessageValid = CRC16_IsMessageValid(rxMessage);
+            bool isSyncValid = memcmp(rxMessage->data, SlaveSyncString, SLAVE_SYNC_STRING_LENGTH) == 0;
+            status = kStatus_Uhk_NoTransfer;
+            *uhkModulePhase = isSyncValid && isMessageValid
+                ? UhkModulePhase_RequestModuleFeatures
+                : UhkModulePhase_RequestSync;
+            break;
+        }
+
         // Get module features
         case UhkModulePhase_RequestModuleFeatures:
             txMessage.data[0] = SlaveCommand_RequestProperty;

right/src/slave_drivers/uhk_module_driver.h

@@ -20,6 +20,9 @@
     } uhk_module_id_t;
 
     typedef enum {
+        UhkModulePhase_RequestSync,
+        UhkModulePhase_ReceiveSync,
+        UhkModulePhase_ProcessSync,
         UhkModulePhase_RequestModuleFeatures,
         UhkModulePhase_ReceiveModuleFeatures,
         UhkModulePhase_ProcessModuleFeatures,

shared/slave_protocol.h

@@ -1,12 +1,19 @@
 #ifndef __SLAVE_PROTOCOL_H__
 #define __SLAVE_PROTOCOL_H__
 
+// Includes:
+
+    #include "fsl_common.h"
+
 // Macros:
 
     #define I2C_MESSAGE_HEADER_LENGTH 3
     #define I2C_MESSAGE_MAX_PAYLOAD_LENGTH 255
     #define I2C_MESSAGE_MAX_TOTAL_LENGTH (I2C_MESSAGE_HEADER_LENGTH + I2C_MESSAGE_MAX_PAYLOAD_LENGTH)
 
+    #define SLAVE_SYNC_STRING "SYNC"
+    #define SLAVE_SYNC_STRING_LENGTH (sizeof(SLAVE_SYNC_STRING) - 1)
+
 // Typedefs:
 
     typedef enum {
@@ -18,6 +25,7 @@
     } slave_command_t;
 
     typedef enum {
+        SlaveProperty_Sync,
         SlaveProperty_Features,
     } slave_property_t;
 
@@ -32,4 +40,8 @@
         uint8_t data[I2C_MESSAGE_MAX_PAYLOAD_LENGTH];
     } __attribute__ ((packed)) i2c_message_t;
 
+// Variables:
+
+    extern char SlaveSyncString[];
+
 #endif