diff --git a/.envrc b/.envrc
new file mode 100644
index 0000000000..1d953f4bd7
--- /dev/null
+++ b/.envrc
@@ -0,0 +1 @@
+use nix
diff --git a/.gitignore b/.gitignore
index ca9f00a733..38791a7412 100644
--- a/.gitignore
+++ b/.gitignore
@@ -116,3 +116,4 @@ compile_commands.json
 # VIA(L) files that don't belong in QMK repo
 via*.json
 /keyboards/**/keymaps/vial/*
+.direnv
diff --git a/keyboards/rkb1/config.h b/keyboards/rkb1/config.h
index c3c99a357b..f3a6d47385 100644
--- a/keyboards/rkb1/config.h
+++ b/keyboards/rkb1/config.h
@@ -3,6 +3,10 @@
 
 #pragma once
 
+#define SPLIT_HAND_PIN GP21
+#define SPLIT_HAND_PIN_LOW_IS_LEFT 
+#define SPLIT_USB_DETECT
+
 /*
  * Feature disable options
  *  These options are also useful to firmware size reduction.
diff --git a/keyboards/rkb1/i2c_master.c b/keyboards/rkb1/i2c_master.c
new file mode 100644
index 0000000000..8a6aebf98e
--- /dev/null
+++ b/keyboards/rkb1/i2c_master.c
@@ -0,0 +1,74 @@
+// rp2040 implementation of i2c_master.c
+#include "i2c_master.h"
+#include "hardware/i2c.h"
+#include "hardware/gpio.h"
+#include <string.h>
+
+void cos_i2c_init(void) {
+    static bool is_initialized = false;
+    if (!is_initialized) {
+        is_initialized = true;
+
+        gpio_set_function(24, GPIO_FUNC_I2C);
+        gpio_set_function(25, GPIO_FUNC_I2C);
+        gpio_pull_up(24);
+        gpio_pull_up(25);
+    }
+}
+
+static bool enabled = false;
+static void init_i2c(void) {
+    if(!enabled)  {
+        i2c_init(i2c0, 100 * 1000); // 100kb/s
+        enabled = true;
+    }
+}
+
+static uint8_t i2c_address;
+
+static i2c_status_t pico_to_qmk(int result) {
+    if(result == PICO_ERROR_TIMEOUT)
+        return I2C_STATUS_TIMEOUT;
+    if(result < 0)
+        return I2C_STATUS_ERROR;
+    return I2C_STATUS_SUCCESS;
+}
+
+i2c_status_t cos_i2c_start(uint8_t address) {
+    i2c_address = address;
+    init_i2c();
+    return I2C_STATUS_SUCCESS;
+}
+
+i2c_status_t cos_i2c_transmit(uint8_t address, const uint8_t *data, uint16_t length, uint16_t timeout) {
+    cos_i2c_start(address);
+    return pico_to_qmk(i2c_write_timeout_us(i2c0, address, data, (size_t)length, false, (uint32_t)timeout * 1000));
+}
+
+i2c_status_t cos_i2c_receive(uint8_t address, uint8_t * data, uint16_t length, uint16_t timeout) {
+    cos_i2c_start(address);
+    return pico_to_qmk(i2c_read_timeout_us(i2c0, address, data, (size_t)length, false, (uint32_t)timeout * 1000));
+}
+
+i2c_status_t cos_i2c_writeReg(uint8_t devaddr, uint8_t regaddr, const uint8_t* data, uint16_t length, uint16_t timeout) {
+    cos_i2c_start(devaddr);
+    uint8_t complete_packet[length + 1];
+    memcpy(complete_packet + 1, data, (size_t)length);
+    complete_packet[0] = regaddr;
+
+    return cos_i2c_transmit(devaddr, complete_packet, length + 1, timeout);
+}
+
+i2c_status_t cos_i2c_readReg(uint8_t devaddr, uint8_t regaddr, uint8_t* data, uint16_t length, uint16_t timeout){
+    cos_i2c_start(devaddr);
+    // TODO: uses 2x timeout
+    i2c_status_t reg_result = cos_i2c_transmit(devaddr, &regaddr, 1, timeout);
+    if(reg_result != I2C_STATUS_SUCCESS)
+        return reg_result;
+    return cos_i2c_receive(devaddr, data, length, timeout);
+}
+
+void cos_i2c_stop(void) {
+    enabled = false;
+    i2c_deinit(i2c0);
+}
diff --git a/keyboards/rkb1/i2c_slave.c b/keyboards/rkb1/i2c_slave.c
new file mode 100644
index 0000000000..63a6f69a9c
--- /dev/null
+++ b/keyboards/rkb1/i2c_slave.c
@@ -0,0 +1,119 @@
+#include "i2c_slave.h"
+#include "hardware/i2c.h"
+#include "hardware/gpio.h"
+#include "hardware/irq.h"
+#include <string.h>
+#include "transactions.h"
+
+// Code taken from here: https://github.com/harsha-vk/weeder_bot/blob/0bb2ac3f627dc2b3867480d210c0536ae0f684a5/assets/raspberry_pi_pico_code/src/i2c_slave.cpp
+
+static volatile bool is_callback_executor = false;
+volatile uint8_t i2c_slave_reg[I2C_SLAVE_REG_COUNT];
+static volatile uint8_t buffer_address;
+static volatile bool    sub_has_register_set = false;
+
+static volatile bool transfer_in_progress = false;
+enum i2c_event_t {
+    I2C_SUB_RECEIVE,
+    I2C_SUB_REQUEST,
+    I2C_SUB_FINISH
+};
+
+static void i2c_sub_handler(enum i2c_event_t event) {
+    //uint8_t ack = 1;
+    switch(event) {
+        case I2C_SUB_RECEIVE: {
+            while(i2c_get_read_available(i2c0)) {
+                if(!sub_has_register_set) {
+                    i2c_read_raw_blocking(i2c0, (uint8_t *)&buffer_address, 1);
+                    if (buffer_address >= I2C_SLAVE_REG_COUNT) {
+                        //ack = 0;
+                        buffer_address = 0;
+                    }
+                    sub_has_register_set = true;
+                    is_callback_executor = buffer_address == split_transaction_table[I2C_EXECUTE_CALLBACK].initiator2target_offset;
+                } else {
+                    // find out how many bytes we can safely read
+                    uint32_t bytes_left = I2C_SLAVE_REG_COUNT - buffer_address;
+                    uint32_t bytes_to_read = i2c_get_read_available(i2c0);
+                    uint32_t num_bytes = (bytes_left < bytes_to_read) ? bytes_left : bytes_to_read;
+                    i2c_read_raw_blocking(i2c0, (uint8_t *)i2c_slave_reg + buffer_address, num_bytes);
+                    buffer_address += num_bytes;
+                    if(buffer_address >= I2C_SLAVE_REG_COUNT)
+                        buffer_address = 0;    
+                    // If we're intending to execute a transaction callback, do so, as we've just received the transaction ID
+                    if (is_callback_executor) {
+                        split_transaction_desc_t *trans = &split_transaction_table[split_shmem->transaction_id];
+                        if (trans->slave_callback) {
+                            trans->slave_callback(trans->initiator2target_buffer_size, split_trans_initiator2target_buffer(trans), trans->target2initiator_buffer_size, split_trans_target2initiator_buffer(trans));
+                        }
+                    }
+                }
+            }
+        }
+        break;
+        case I2C_SUB_REQUEST: {
+            i2c_write_raw_blocking(i2c0, (uint8_t*)i2c_slave_reg + buffer_address, 1);
+            buffer_address++;
+            break;
+        }
+        case I2C_SUB_FINISH:
+            sub_has_register_set = false;
+            is_callback_executor = false;
+            break;
+    }
+    // TODO: ack??
+}
+
+static void finish_transfer(void) {
+    transfer_in_progress = false;
+    i2c_sub_handler(I2C_SUB_FINISH);
+}
+
+static void i2c_handler(void) {
+    i2c_hw_t *hw = i2c_get_hw(i2c0);
+    uint32_t intr_stat = hw->intr_stat;
+    if(intr_stat == 0) return; // spurious
+    if(intr_stat & I2C_IC_INTR_STAT_R_TX_ABRT_BITS) {
+        hw->clr_tx_abrt;
+        finish_transfer();
+    }
+    if(intr_stat & I2C_IC_INTR_STAT_R_START_DET_BITS) {
+        hw->clr_start_det;
+        finish_transfer();
+    }
+    if(intr_stat & I2C_IC_INTR_STAT_R_STOP_DET_BITS) {
+        hw->clr_stop_det;
+        finish_transfer();
+    }
+    if(intr_stat & I2C_IC_INTR_STAT_R_RX_FULL_BITS) {
+        transfer_in_progress = true;
+        i2c_sub_handler(I2C_SUB_RECEIVE);
+    }
+    if(intr_stat & I2C_IC_INTR_STAT_R_RD_REQ_BITS) {
+        hw->clr_rd_req;
+        transfer_in_progress = true;
+        i2c_sub_handler(I2C_SUB_REQUEST);
+    }
+}
+
+void cos_i2c_slave_init(uint8_t address) {
+    i2c_init(i2c0, 100 * 1000);
+    i2c_set_slave_mode(i2c0, true, address);
+    gpio_set_function(24, GPIO_FUNC_I2C);
+    gpio_set_function(25, GPIO_FUNC_I2C);
+    gpio_pull_up(24);
+    gpio_pull_up(25);
+
+    i2c_hw_t *hw = i2c_get_hw(i2c0);
+    hw->intr_mask = I2C_IC_INTR_MASK_M_RX_FULL_BITS | I2C_IC_INTR_MASK_M_RD_REQ_BITS | I2C_IC_RAW_INTR_STAT_TX_ABRT_BITS | I2C_IC_INTR_MASK_M_STOP_DET_BITS | I2C_IC_INTR_MASK_M_START_DET_BITS;
+    irq_set_exclusive_handler(I2C0_IRQ, i2c_handler);
+    irq_set_enabled(I2C0_IRQ, true);
+}
+
+void cos_i2c_slave_stop(void) {
+    i2c_set_slave_mode(i2c0, false, 0);
+    i2c_deinit(i2c0);
+}
+
+
diff --git a/keyboards/rkb1/i2c_slave.h b/keyboards/rkb1/i2c_slave.h
new file mode 100644
index 0000000000..e1f390eef8
--- /dev/null
+++ b/keyboards/rkb1/i2c_slave.h
@@ -0,0 +1,41 @@
+/*  Copyright (C) 2019 Elia Ritterbusch
+ +
+ *  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/>.
+ */
+/* Library made by: g4lvanix
+ * GitHub repository: https://github.com/g4lvanix/I2C-slave-lib
+
+ Info: Inititate the library by giving the required address.
+       Read or write to the necessary buffer according to the opperation.
+ */
+
+#pragma once
+
+#ifndef I2C_SLAVE_REG_COUNT
+
+#    if defined(USE_I2C) && defined(SPLIT_COMMON_TRANSACTIONS)
+#        include "transport.h"
+#        define I2C_SLAVE_REG_COUNT sizeof(split_shared_memory_t)
+#    else // defined(USE_I2C) && defined(SPLIT_COMMON_TRANSACTIONS)
+#        define I2C_SLAVE_REG_COUNT 30
+#    endif // defined(USE_I2C) && defined(SPLIT_COMMON_TRANSACTIONS)
+
+#endif // I2C_SLAVE_REG_COUNT
+
+_Static_assert(I2C_SLAVE_REG_COUNT < 256, "I2C target registers must be single byte");
+
+extern volatile uint8_t i2c_slave_reg[I2C_SLAVE_REG_COUNT];
+
+void cos_i2c_slave_init(uint8_t address);
+void cos_i2c_slave_stop(void);
diff --git a/keyboards/rkb1/rules.mk b/keyboards/rkb1/rules.mk
index 6e7633bfe0..cf1cb994a5 100644
--- a/keyboards/rkb1/rules.mk
+++ b/keyboards/rkb1/rules.mk
@@ -1 +1,9 @@
-# This file intentionally left blank
+SPLIT_KEYBOARD = yes
+SPLIT_TRANSPORT = custom
+RP2040_INTRINSICS_ENABLED = yes
+
+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)
diff --git a/platforms/chibios/drivers/i2c_master.c b/platforms/chibios/drivers/i2c_master.c
index ad11d850dd..c0f2d6c726 100644
--- a/platforms/chibios/drivers/i2c_master.c
+++ b/platforms/chibios/drivers/i2c_master.c
@@ -207,4 +207,4 @@ __attribute__((weak)) i2c_status_t i2c_ping_address(uint8_t address, uint16_t ti
     // This approach may produce false negative results for I2C devices that do not respond to a register 0 read request.
     uint8_t data = 0;
     return i2c_readReg(address, 0, &data, sizeof(data), timeout);
-}
\ No newline at end of file
+}
diff --git a/platforms/chibios/drivers/wear_leveling/wear_leveling_rp2040_flash_config.h b/platforms/chibios/drivers/wear_leveling/wear_leveling_rp2040_flash_config.h
index e1e2433601..88dd369b4e 100644
--- a/platforms/chibios/drivers/wear_leveling/wear_leveling_rp2040_flash_config.h
+++ b/platforms/chibios/drivers/wear_leveling/wear_leveling_rp2040_flash_config.h
@@ -3,6 +3,13 @@
 #pragma once
 
 #ifndef __ASSEMBLER__
+#define _PICO_ASSERT_H
+#include <stdbool.h>
+#include <assert.h>
+#define PARAM_ASSERTIONS_ENABLED(x) /* x */
+#define invalid_params_if(x, test) /* x test */
+#define valid_params_if(x, test) /* x test */
+#define hard_assert_if(x, test) /* x test */
 #    include "hardware/flash.h"
 #endif
 
@@ -30,3 +37,4 @@
 #ifndef WEAR_LEVELING_RP2040_FLASH_BASE
 #    define WEAR_LEVELING_RP2040_FLASH_BASE ((WEAR_LEVELING_RP2040_FLASH_SIZE) - (WEAR_LEVELING_BACKING_SIZE))
 #endif
+
diff --git a/platforms/chibios/vendors/RP/RP2040.mk b/platforms/chibios/vendors/RP/RP2040.mk
index 94f023d72b..df450704ba 100644
--- a/platforms/chibios/vendors/RP/RP2040.mk
+++ b/platforms/chibios/vendors/RP/RP2040.mk
@@ -31,7 +31,20 @@ PICOSDKSRC     = $(PICOSDKROOT)/src/rp2_common/hardware_clocks/clocks.c \
                  $(PICOSDKROOT)/src/rp2_common/hardware_claim/claim.c \
                  $(PICOSDKROOT)/src/rp2_common/hardware_watchdog/watchdog.c \
                  $(PICOSDKROOT)/src/rp2_common/hardware_xosc/xosc.c \
-                 $(PICOSDKROOT)/src/rp2_common/pico_bootrom/bootrom.c
+                 $(PICOSDKROOT)/src/rp2_common/hardware_i2c/i2c.c \
+                 $(PICOSDKROOT)/src/rp2_common/hardware_irq/irq.c \
+                 $(PICOSDKROOT)/src/rp2_common/hardware_irq/irq_handler_chain.S \
+                 $(PICOSDKROOT)/src/rp2_common/hardware_timer/timer.c \
+                 $(PICOSDKROOT)/src/rp2_common/pico_bootrom/bootrom.c \
+                 $(PICOSDKROOT)/src/common/pico_time/time.c \
+                 $(PICOSDKROOT)/src/common/pico_time/timeout_helper.c \
+                 $(PICOSDKROOT)/src/common/pico_util/datetime.c \
+                 $(PICOSDKROOT)/src/common/pico_util/pheap.c \
+                 $(PICOSDKROOT)/src/common/pico_util/queue.c \
+                 $(PICOSDKROOT)/src/common/pico_sync/critical_section.c \
+                 $(PICOSDKROOT)/src/common/pico_sync/lock_core.c \
+                 $(PICOSDKROOT)/src/common/pico_sync/mutex.c \
+                 $(PICOSDKROOT)/src/common/pico_sync/sem.c \
 
 PICOSDKINC     = $(CHIBIOS)//os/various/pico_bindings/dumb/include \
                  $(PICOSDKROOT)/src/common/pico_base/include \
@@ -49,10 +62,15 @@ PICOSDKINC     = $(CHIBIOS)//os/various/pico_bindings/dumb/include \
                  $(PICOSDKROOT)/src/rp2_common/hardware_resets/include \
                  $(PICOSDKROOT)/src/rp2_common/hardware_watchdog/include \
                  $(PICOSDKROOT)/src/rp2_common/hardware_xosc/include \
+                 $(PICOSDKROOT)/src/rp2_common/hardware_i2c/include \
+                 $(PICOSDKROOT)/src/rp2_common/hardware_timer/include \
                  $(PICOSDKROOT)/src/rp2040/hardware_regs/include \
                  $(PICOSDKROOT)/src/rp2040/hardware_structs/include \
                  $(PICOSDKROOT)/src/boards/include \
-                 $(PICOSDKROOT)/src/rp2_common/pico_bootrom/include
+                 $(PICOSDKROOT)/src/rp2_common/pico_bootrom/include \
+                 $(PICOSDKROOT)/src/common/pico_time/include \
+                 $(PICOSDKROOT)/src/common/pico_util/include \
+                 $(PICOSDKROOT)/src/common/pico_sync/include 
 
 PLATFORM_SRC += $(PICOSDKSRC)
 EXTRAINCDIRS += $(PICOSDKINC)
diff --git a/quantum/split_common/transport.c b/quantum/split_common/transport.c
index 83edc34859..6eb981ac94 100644
--- a/quantum/split_common/transport.c
+++ b/quantum/split_common/transport.c
@@ -128,3 +128,4 @@ bool transport_master(matrix_row_t master_matrix[], matrix_row_t slave_matrix[])
 void transport_slave(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]) {
     transactions_slave(master_matrix, slave_matrix);
 }
+