4 files changed, 115 insertions, 0 deletions
diff --git a/tmk_core/common.mk b/tmk_core/common.mk
index fdf2aa0972..05839824c0 100644
--- a/tmk_core/common.mk
+++ b/tmk_core/common.mk
@@ -18,6 +18,7 @@ TMK_COMMON_SRC +=	$(COMMON_DIR)/host.c \
 	$(COMMON_DIR)/report.c \
 	$(PLATFORM_COMMON_DIR)/suspend.c \
 	$(PLATFORM_COMMON_DIR)/timer.c \
+	$(COMMON_DIR)/sync_timer.c \
 	$(PLATFORM_COMMON_DIR)/bootloader.c \
 
 ifeq ($(PLATFORM),AVR)
diff --git a/tmk_core/common/keyboard.c b/tmk_core/common/keyboard.c
index 8c7bdc8b55..a1fbc01da6 100644
--- a/tmk_core/common/keyboard.c
+++ b/tmk_core/common/keyboard.c
@@ -23,6 +23,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "led.h"
 #include "keycode.h"
 #include "timer.h"
+#include "sync_timer.h"
 #include "print.h"
 #include "debug.h"
 #include "command.h"
@@ -255,6 +256,7 @@ __attribute__((weak)) void housekeeping_task_user(void) {}
  */
 void keyboard_init(void) {
     timer_init();
+    sync_timer_init();
     matrix_init();
 #ifdef VIA_ENABLE
     via_init();
diff --git a/tmk_core/common/sync_timer.c b/tmk_core/common/sync_timer.c
new file mode 100644
index 0000000000..de24b463b6
--- /dev/null
+++ b/tmk_core/common/sync_timer.c
@@ -0,0 +1,58 @@
+/*
+Copyright (C) 2020 Ryan Caltabiano <https://github.com/XScorpion2>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the "Software"), to deal in
+the Software without restriction, including without limitation the rights to
+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
+of the Software, and to permit persons to whom the Software is furnished to do
+so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+If you happen to meet one of the copyright holders in a bar you are obligated
+to buy them one pint of beer.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+*/
+
+#include "sync_timer.h"
+#include "keyboard.h"
+
+#if defined(SPLIT_KEYBOARD) && !defined(DISABLE_SYNC_TIMER)
+volatile int32_t sync_timer_ms;
+
+void sync_timer_init(void) { sync_timer_ms = 0; }
+
+void sync_timer_update(uint32_t time) {
+    if (is_keyboard_master()) return;
+    sync_timer_ms = time - timer_read32();
+}
+
+uint16_t sync_timer_read(void) {
+    if (is_keyboard_master()) return timer_read();
+    return sync_timer_read32();
+}
+
+uint32_t sync_timer_read32(void) {
+    if (is_keyboard_master()) return timer_read32();
+    return sync_timer_ms + timer_read32();
+}
+
+uint16_t sync_timer_elapsed(uint16_t last) {
+    if (is_keyboard_master()) return timer_elapsed(last);
+    return TIMER_DIFF_16(sync_timer_read(), last);
+}
+
+uint32_t sync_timer_elapsed32(uint32_t last) {
+    if (is_keyboard_master()) return timer_elapsed32(last);
+    return TIMER_DIFF_32(sync_timer_read32(), last);
+}
+#endif
diff --git a/tmk_core/common/sync_timer.h b/tmk_core/common/sync_timer.h
new file mode 100644
index 0000000000..9ddef45bb2
--- /dev/null
+++ b/tmk_core/common/sync_timer.h
@@ -0,0 +1,54 @@
+/*
+Copyright (C) 2020 Ryan Caltabiano <https://github.com/XScorpion2>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the "Software"), to deal in
+the Software without restriction, including without limitation the rights to
+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
+of the Software, and to permit persons to whom the Software is furnished to do
+so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+If you happen to meet one of the copyright holders in a bar you are obligated
+to buy them one pint of beer.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+*/
+
+#pragma once
+
+#include <stdint.h>
+#include "timer.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#if defined(SPLIT_KEYBOARD) && !defined(DISABLE_SYNC_TIMER)
+void     sync_timer_init(void);
+void     sync_timer_update(uint32_t time);
+uint16_t sync_timer_read(void);
+uint32_t sync_timer_read32(void);
+uint16_t sync_timer_elapsed(uint16_t last);
+uint32_t sync_timer_elapsed32(uint32_t last);
+#else
+#    define sync_timer_init()
+#    define sync_timer_clear()
+#    define sync_timer_update(t)
+#    define sync_timer_read() timer_read()
+#    define sync_timer_read32() timer_read32()
+#    define sync_timer_elapsed(t) timer_elapsed(t)
+#    define sync_timer_elapsed32(t) timer_elapsed32(t)
+#endif
+
+#ifdef __cplusplus
+}
+#endif