diff --git a/software/sys_controller/ossc/av_controller.c b/software/sys_controller/ossc/av_controller.c
index 6e58c67..d4d7d81 100644
--- a/software/sys_controller/ossc/av_controller.c
+++ b/software/sys_controller/ossc/av_controller.c
@@ -1235,8 +1235,9 @@ int main()
         while (alt_timestamp() < start_ts + MAINLOOP_INTERVAL_US*(TIMER_0_FREQ/1000000)) {}
 
         // restart timer if past half-range
-        if (start_ts > 0x7fffffff) {
+        if ((start_ts > 0x7fffffff) && !SPI_Timer_Status()) {
             alt_timestamp_start();
+            SPI_Timer_Off();
             if (auto_input_timestamp > start_ts)
                 auto_input_timestamp -= start_ts;
             else
diff --git a/software/sys_controller/ulibSD/spi_io.c b/software/sys_controller/ulibSD/spi_io.c
index a9172b9..89f193e 100644
--- a/software/sys_controller/ulibSD/spi_io.c
+++ b/software/sys_controller/ulibSD/spi_io.c
@@ -58,8 +58,7 @@ inline void SPI_Freq_Low (void) {
 
 int SPI_Timer_On (WORD ms) {
     if (!sd_timer_ts) {
-        sd_timer_ts = ms*(ALT_CPU_FREQ/1000);
-        alt_timestamp_start();
+        sd_timer_ts = alt_timestamp() + ms*(TIMER_0_FREQ/1000);
         return 0;
     }
     return 1;