From 6f0009cfbbc76fd7216570bbf6115e2700083aed Mon Sep 17 00:00:00 2001
From: Hector van der Aa <hector@h3cx.dev>
Date: Wed, 3 Jun 2026 19:11:50 +0200
Subject: [PATCH] Fixed critical ring buffer underflow bug

---
 STM32/CM7/Core/Inc/global_state.h | 2 +-
 STM32/CM7/Core/Src/ring_buffer.c  | 4 +++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/STM32/CM7/Core/Inc/global_state.h b/STM32/CM7/Core/Inc/global_state.h
index 0840d00..d7bd3d6 100644
--- a/STM32/CM7/Core/Inc/global_state.h
+++ b/STM32/CM7/Core/Inc/global_state.h
@@ -7,7 +7,7 @@
 #include <stdint.h>
 
 #define MAX_CAM_MISS 2
-#define SPARK_ADVANCE 20
+#define SPARK_ADVANCE 40
 #define INJECTION_PHASE 0
 
 typedef enum { SYNC_OK = 0, SYNC_PENDING = 1, SYNC_NOT_OK = 2 } sync_state_t;
diff --git a/STM32/CM7/Core/Src/ring_buffer.c b/STM32/CM7/Core/Src/ring_buffer.c
index f42d79a..e8e3127 100644
--- a/STM32/CM7/Core/Src/ring_buffer.c
+++ b/STM32/CM7/Core/Src/ring_buffer.c
@@ -5,6 +5,7 @@
 #include <assert.h>
 #include <ring_buffer.h>
 #include <stdbool.h>
+#include <stdint.h>
 
 void ringBufferPush(volatile ring_buffer_t *rb, uint32_t value) {
   rb->buffer[rb->w_head] = value;
@@ -13,7 +14,8 @@ void ringBufferPush(volatile ring_buffer_t *rb, uint32_t value) {
 }
 
 uint32_t ringBufferRead(volatile ring_buffer_t *rb, uint8_t neg_idx) {
-  return rb->buffer[rb->w_head - 1 - neg_idx];
+  uint8_t idx = (uint8_t)(rb->w_head - 1u - neg_idx);
+  return rb->buffer[idx];
 }
 
 void ringBufferRevert(volatile ring_buffer_t *rb, uint8_t val) {