HAL_ChibiOS: fixed bouncebuffer code on STM32F7

libraries/AP_HAL_ChibiOS/hwdef/common/bouncebuffer.c

@@ -24,9 +24,10 @@
 #if defined(STM32H7)
 // always use a bouncebuffer on H7, to ensure alignment and padding
 #define IS_DMA_SAFE(addr) false
-#elif defined(DTCM_RAM_SIZE_KB)
-// on F7 and H7 we check we are in the DTCM region, and 16 bit aligned
-#define IS_DMA_SAFE(addr) ((((uint32_t)(addr)) & ((0xFFFFFFFF & ~(DTCM_RAM_SIZE_KB*1024U-1)) | 1U)) == 0x20000000)
+#elif defined(STM32F7)
+// on F76x we only consider first half of DTCM memory as DMA safe, 2nd half is used as fast memory for EKF
+// on F74x we only have 64k of DTCM
+#define IS_DMA_SAFE(addr) ((((uint32_t)(addr)) & ((0xFFFFFFFF & ~(64*1024U-1)) | 1U)) == 0x20000000)
 #else
 // this checks an address is in main memory and 16 bit aligned
 #define IS_DMA_SAFE(addr) ((((uint32_t)(addr)) & 0xF0000001) == 0x20000000)

libraries/AP_HAL_ChibiOS/hwdef/scripts/STM32F767xx.py

@@ -35,7 +35,9 @@ mcu = {
     # flags of 2 means faster memory for CPU intensive work
     'RAM_MAP' : [
         (0x20020000, 384, 0), # SRAM1/SRAM2
-        (0x20000000, 128, 1), # DTCM, DMA
+        # split DTCM in two to allow for fast checking of IS_DMA_SAFE in bouncebuffer code
+        (0x20000000,  64, 1), # DTCM, DMA safe
+        (0x20010000,  64, 2), # DTCM, 2nd half, used as fast memory. This lowers memory contention in the EKF code
     ]
 }