HAL_ChibiOS: flush all memory on chSysHalt()

this makes debugging a lot easier, as gdb can see the values in dcache

libraries/AP_HAL_ChibiOS/hwdef/common/chconf.h

@@ -520,11 +520,13 @@
  * @brief   System halt hook.
  * @details This hook is invoked in case to a system halting error before
  *          the system is halted.
+ *
+ * We flush all memory on STM32F7 to allow gdb to access variables currently
+ * in the dcache
  */
-
 #define CH_CFG_SYSTEM_HALT_HOOK(reason) do {                               \
-        extern int printf(const char *fmt, ...); \
-        printf(reason); \
+        extern void memory_flush_all(void); \
+        memory_flush_all(); \
 } while(0)
 
 /**

libraries/AP_HAL_ChibiOS/hwdef/common/stm32_util.c

@@ -17,6 +17,7 @@
 #include <stdint.h>
 #include <stdio.h>
 #include <string.h>
+#include <stm32_dma.h>
 
 void stm32_timer_set_input_filter(stm32_tim_t *tim, uint8_t channel, uint8_t filter_mode)
 {
@@ -54,3 +55,13 @@ void show_stack_usage(void)
   } while (tp != NULL);
 }
 #endif
+
+/*
+  flush all memory. Used in chSysHalt()
+ */
+void memory_flush_all(void)
+{
+#if defined(STM32F7) && STM32_DMA_CACHE_HANDLING == TRUE
+    dmaBufferFlush(HAL_RAM_BASE_ADDRESS, HAL_RAM_SIZE_KB * 1024U);
+#endif
+}