refine xor flip to ensure we only flip once per millisecond (#479)

Author: trentgill

ll/status_led.c

@@ -1,9 +1,12 @@
 #include "status_led.h"
 
+#include <stdbool.h>
+
 // LED on GPIO A15
 
 static GPIO_InitTypeDef GPIO_IS;
 static LED_SPEED fast_blink;
+static bool do_flip = false;
 
 void status_led_init(void){
     // activate peripheral clock
@@ -21,9 +24,12 @@ void status_led_init(void){
 // call this at a regular interval (designed for 1ms interval)
 uint32_t next_flip = 0;
 void status_led_tick(uint32_t time_now){
-    if(time_now > next_flip){
-        status_led_xor();
+    if(time_now > next_flip // time to animate timer
+    || (do_flip && fast_blink)){ // xor event & USB connected
+        // status_led_xor();
+        HAL_GPIO_TogglePin(GPIOA, GPIO_PIN_15);
         next_flip = time_now + (fast_blink ? 2000 : 500);
+        do_flip = false;
     }
 }
 
@@ -36,5 +42,6 @@ void status_led_set(uint8_t is_on){
 }
 
 void status_led_xor(void){
-    HAL_GPIO_TogglePin(GPIOA, GPIO_PIN_15);
+    // HAL_GPIO_TogglePin(GPIOA, GPIO_PIN_15);
+    do_flip = true;
 }