diff --git a/drivers/chibios/serial.c b/drivers/chibios/serial.c
new file mode 100644
index 0000000000..26c6806532
--- /dev/null
+++ b/drivers/chibios/serial.c
@@ -0,0 +1,290 @@
+/*
+ * WARNING: be careful changing this code, it is very timing dependent
+ */
+
+#include "quantum.h"
+#include "serial.h"
+#include "wait.h"
+
+#include "hal.h"
+
+// TODO: resolve/remove build warnings
+#if defined(RGBLIGHT_ENABLE) && defined(RGBLED_SPLIT) && defined(PROTOCOL_CHIBIOS) && defined(WS2812_DRIVER_BITBANG)
+# warning "RGBLED_SPLIT not supported with bitbang WS2812 driver"
+#endif
+
+// default wait implementation cannot be called within interrupt
+// this method seems to be more accurate than GPT timers
+#if PORT_SUPPORTS_RT == FALSE
+# error "chSysPolledDelayX method not supported on this platform"
+#else
+# undef wait_us
+# define wait_us(x) chSysPolledDelayX(US2RTC(STM32_SYSCLK, x))
+#endif
+
+#ifndef SELECT_SOFT_SERIAL_SPEED
+# define SELECT_SOFT_SERIAL_SPEED 1
+// TODO: correct speeds...
+// 0: about 189kbps (Experimental only)
+// 1: about 137kbps (default)
+// 2: about 75kbps
+// 3: about 39kbps
+// 4: about 26kbps
+// 5: about 20kbps
+#endif
+
+// Serial pulse period in microseconds. At the moment, going lower than 12 causes communication failure
+#if SELECT_SOFT_SERIAL_SPEED == 0
+# define SERIAL_DELAY 12
+#elif SELECT_SOFT_SERIAL_SPEED == 1
+# define SERIAL_DELAY 16
+#elif SELECT_SOFT_SERIAL_SPEED == 2
+# define SERIAL_DELAY 24
+#elif SELECT_SOFT_SERIAL_SPEED == 3
+# define SERIAL_DELAY 32
+#elif SELECT_SOFT_SERIAL_SPEED == 4
+# define SERIAL_DELAY 48
+#elif SELECT_SOFT_SERIAL_SPEED == 5
+# define SERIAL_DELAY 64
+#else
+# error invalid SELECT_SOFT_SERIAL_SPEED value
+#endif
+
+inline static void serial_delay(void) { wait_us(SERIAL_DELAY); }
+inline static void serial_delay_half(void) { wait_us(SERIAL_DELAY / 2); }
+inline static void serial_delay_blip(void) { wait_us(1); }
+inline static void serial_output(void) { setPinOutput(SOFT_SERIAL_PIN); }
+inline static void serial_input(void) { setPinInputHigh(SOFT_SERIAL_PIN); }
+inline static bool serial_read_pin(void) { return !!readPin(SOFT_SERIAL_PIN); }
+inline static void serial_low(void) { writePinLow(SOFT_SERIAL_PIN); }
+inline static void serial_high(void) { writePinHigh(SOFT_SERIAL_PIN); }
+
+void interrupt_handler(void *arg);
+
+// Use thread + palWaitLineTimeout instead of palSetLineCallback
+// - Methods like setPinOutput and palEnableLineEvent/palDisableLineEvent
+// cause the interrupt to lock up, which would limit to only receiving data...
+static THD_WORKING_AREA(waThread1, 128);
+static THD_FUNCTION(Thread1, arg) {
+ (void)arg;
+ chRegSetThreadName("blinker");
+ while (true) {
+ palWaitLineTimeout(SOFT_SERIAL_PIN, TIME_INFINITE);
+ interrupt_handler(NULL);
+ }
+}
+
+static SSTD_t *Transaction_table = NULL;
+static uint8_t Transaction_table_size = 0;
+
+void soft_serial_initiator_init(SSTD_t *sstd_table, int sstd_table_size) {
+ Transaction_table = sstd_table;
+ Transaction_table_size = (uint8_t)sstd_table_size;
+
+ serial_output();
+ serial_high();
+}
+
+void soft_serial_target_init(SSTD_t *sstd_table, int sstd_table_size) {
+ Transaction_table = sstd_table;
+ Transaction_table_size = (uint8_t)sstd_table_size;
+
+ serial_input();
+
+ palEnablePadEvent(PAL_PORT(SOFT_SERIAL_PIN), PAL_PAD(SOFT_SERIAL_PIN), PAL_EVENT_MODE_FALLING_EDGE);
+ chThdCreateStatic(waThread1, sizeof(waThread1), HIGHPRIO, Thread1, NULL);
+}
+
+// Used by the master to synchronize timing with the slave.
+static void __attribute__((noinline)) sync_recv(void) {
+ serial_input();
+ // This shouldn't hang if the slave disconnects because the
+ // serial line will float to high if the slave does disconnect.
+ while (!serial_read_pin()) {
+ }
+
+ serial_delay();
+}
+
+// Used by the slave to send a synchronization signal to the master.
+static void __attribute__((noinline)) sync_send(void) {
+ serial_output();
+
+ serial_low();
+ serial_delay();
+
+ serial_high();
+}
+
+// Reads a byte from the serial line
+static uint8_t __attribute__((noinline)) serial_read_byte(void) {
+ uint8_t byte = 0;
+ serial_input();
+ for (uint8_t i = 0; i < 8; ++i) {
+ byte = (byte << 1) | serial_read_pin();
+ serial_delay();
+ }
+
+ return byte;
+}
+
+// Sends a byte with MSB ordering
+static void __attribute__((noinline)) serial_write_byte(uint8_t data) {
+ uint8_t b = 8;
+ serial_output();
+ while (b--) {
+ if (data & (1 << b)) {
+ serial_high();
+ } else {
+ serial_low();
+ }
+ serial_delay();
+ }
+}
+
+// interrupt handle to be used by the slave device
+void interrupt_handler(void *arg) {
+ chSysLockFromISR();
+
+ sync_send();
+
+ // read mid pulses
+ serial_delay_blip();
+
+ uint8_t checksum_computed = 0;
+ int sstd_index = 0;
+
+#ifdef SERIAL_USE_MULTI_TRANSACTION
+ sstd_index = serial_read_byte();
+ sync_send();
+#endif
+
+ SSTD_t *trans = &Transaction_table[sstd_index];
+ for (int i = 0; i < trans->initiator2target_buffer_size; ++i) {
+ trans->initiator2target_buffer[i] = serial_read_byte();
+ sync_send();
+ checksum_computed += trans->initiator2target_buffer[i];
+ }
+ checksum_computed ^= 7;
+ uint8_t checksum_received = serial_read_byte();
+ sync_send();
+
+ // wait for the sync to finish sending
+ serial_delay();
+
+ uint8_t checksum = 0;
+ for (int i = 0; i < trans->target2initiator_buffer_size; ++i) {
+ serial_write_byte(trans->target2initiator_buffer[i]);
+ sync_send();
+ serial_delay_half();
+ checksum += trans->target2initiator_buffer[i];
+ }
+ serial_write_byte(checksum ^ 7);
+ sync_send();
+
+ // wait for the sync to finish sending
+ serial_delay();
+
+ *trans->status = (checksum_computed == checksum_received) ? TRANSACTION_ACCEPTED : TRANSACTION_DATA_ERROR;
+
+ // end transaction
+ serial_input();
+
+ // TODO: remove extra delay between transactions
+ serial_delay();
+
+ chSysUnlockFromISR();
+}
+
+/////////
+// start transaction by initiator
+//
+// int soft_serial_transaction(int sstd_index)
+//
+// Returns:
+// TRANSACTION_END
+// TRANSACTION_NO_RESPONSE
+// TRANSACTION_DATA_ERROR
+// this code is very time dependent, so we need to disable interrupts
+#ifndef SERIAL_USE_MULTI_TRANSACTION
+int soft_serial_transaction(void) {
+ int sstd_index = 0;
+#else
+int soft_serial_transaction(int sstd_index) {
+#endif
+
+ if (sstd_index > Transaction_table_size) return TRANSACTION_TYPE_ERROR;
+ SSTD_t *trans = &Transaction_table[sstd_index];
+
+ // TODO: remove extra delay between transactions
+ serial_delay();
+
+ // this code is very time dependent, so we need to disable interrupts
+ chSysLock();
+
+ // signal to the slave that we want to start a transaction
+ serial_output();
+ serial_low();
+ serial_delay_blip();
+
+ // wait for the slaves response
+ serial_input();
+ serial_high();
+ serial_delay();
+
+ // check if the slave is present
+ if (serial_read_pin()) {
+ // slave failed to pull the line low, assume not present
+ dprintf("serial::NO_RESPONSE\n");
+ chSysUnlock();
+ return TRANSACTION_NO_RESPONSE;
+ }
+
+ // if the slave is present syncronize with it
+
+ uint8_t checksum = 0;
+ // send data to the slave
+#ifdef SERIAL_USE_MULTI_TRANSACTION
+ serial_write_byte(sstd_index); // first chunk is transaction id
+ sync_recv();
+#endif
+ for (int i = 0; i < trans->initiator2target_buffer_size; ++i) {
+ serial_write_byte(trans->initiator2target_buffer[i]);
+ sync_recv();
+ checksum += trans->initiator2target_buffer[i];
+ }
+ serial_write_byte(checksum ^ 7);
+ sync_recv();
+
+ serial_delay();
+ serial_delay(); // read mid pulses
+
+ // receive data from the slave
+ uint8_t checksum_computed = 0;
+ for (int i = 0; i < trans->target2initiator_buffer_size; ++i) {
+ trans->target2initiator_buffer[i] = serial_read_byte();
+ sync_recv();
+ checksum_computed += trans->target2initiator_buffer[i];
+ }
+ checksum_computed ^= 7;
+ uint8_t checksum_received = serial_read_byte();
+
+ sync_recv();
+ serial_delay();
+
+ if ((checksum_computed) != (checksum_received)) {
+ dprintf("serial::FAIL[%u,%u,%u]\n", checksum_computed, checksum_received, sstd_index);
+ serial_output();
+ serial_high();
+
+ chSysUnlock();
+ return TRANSACTION_DATA_ERROR;
+ }
+
+ // always, release the line when not in use
+ serial_high();
+ serial_output();
+
+ chSysUnlock();
+ return TRANSACTION_END;
+}
diff --git a/quantum/stm32/halconf.h b/quantum/stm32/halconf.h
index 533803a25f..b6c7b392ca 100644
--- a/quantum/stm32/halconf.h
+++ b/quantum/stm32/halconf.h
@@ -203,7 +203,7 @@
* @note Disabling this option saves both code and data space.
*/
# if !defined(PAL_USE_CALLBACKS) || defined(__DOXYGEN__)
-# define PAL_USE_CALLBACKS FALSE
+# define PAL_USE_CALLBACKS TRUE
# endif
/**
@@ -211,7 +211,7 @@
* @note Disabling this option saves both code and data space.
*/
# if !defined(PAL_USE_WAIT) || defined(__DOXYGEN__)
-# define PAL_USE_WAIT FALSE
+# define PAL_USE_WAIT TRUE
# endif
/*===========================================================================*/