finally get split keyboard comms working

keyboards/rkb1/config.h

@@ -17,6 +17,11 @@
 
 #define ONESHOT_TAP_TOGGLE 2
 
+#define SERIAL_USART_HALF_DUPLEX
+#define SERIAL_USART_TX_PIN GP18
+//#define SERIAL_USART_RX_PIN GP19
+//#define SERIAL_USART_PIN_SWAP
+
 /*
  * Feature disable options
  *  These options are also useful to firmware size reduction.

keyboards/rkb1/info.json

@@ -36,7 +36,7 @@
             }
         },
         "transport": {
-            "protocol": "custom"
+            "protocol": "serial"
         },
         "usb_detect": {
             "enabled": true

keyboards/rkb1/rules.mk

@@ -1,15 +1,17 @@
 UNICODE_ENABLE = yes
 
-OLED_ENABLE = yes
-OLED_DRIVER = SSD1306
+#OLED_ENABLE = yes
+#OLED_DRIVER = SSD1306
 
-SRC += i2c_slave.c i2c_master.c
-QUANTUM_SRC += $(QUANTUM_DIR)/split_common/transport.c $(QUANTUM_DIR)/split_common/transactions.c
-OPT_DEFS += -DSPLIT_COMMON_TRANSACTIONS
-COMMON_VPATH += $(QUANTUM_PATH)/split_common
-EXTRAINCDIRS += $(BOARD_PATH)
+#SRC += i2c_slave.c i2c_master.c
+#QUANTUM_SRC += $(QUANTUM_DIR)/split_common/transport.c $(QUANTUM_DIR)/split_common/transactions.c
+#OPT_DEFS += -DSPLIT_COMMON_TRANSACTIONS
+#COMMON_VPATH += $(QUANTUM_PATH)/split_common
+#EXTRAINCDIRS += $(BOARD_PATH)
 
 CFLAGS += -Wl,--defsym=__unhandled_user_irq=_unhandled_exception
 
 #SRC += matrix.c
 #CUSTOM_MATRIX = lite
+
+SERIAL_DRIVER = vendor

platforms/chibios/drivers/vendor/RP/RP2040/serial_vendor.c

@@ -3,6 +3,8 @@
 
 #include "serial_usart.h"
 #include "serial_protocol.h"
+#undef PARAM_ASSERTIONS_ENABLED
+#define PARAM_ASSERTIONS_ENABLED(x) 0
 #include "hardware/pio.h"
 #include "hardware/clocks.h"
 #include "wait.h"

quantum/split_common/transport.c

@@ -22,7 +22,7 @@
 #include "transaction_id_define.h"
 #include "atomic_util.h"
 
-#if 1
+#if USE_I2C
 
 #    ifndef SLAVE_I2C_TIMEOUT
 #        define SLAVE_I2C_TIMEOUT 100