From bd413f1d82dc80f93209dc82aab29bd45330584c Mon Sep 17 00:00:00 2001
From: Kevin Bracey <kevin.bracey@arm.com>
Date: Tue, 6 Nov 2018 16:45:45 +0200
Subject: [PATCH] Disable write buffer in debug builds (M3/M4)

As part of work to improve the debugging of exceptions, have
Mbed OS make an effort to make exceptions more precise in debug builds
at the cost of performance.

Related pyOCD work:

   https://github.com/mbedmicro/pyOCD/pull/430
---
 platform/mbed_application.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/platform/mbed_application.c b/platform/mbed_application.c
index b55519491b..41930fcd65 100644
--- a/platform/mbed_application.c
+++ b/platform/mbed_application.c
@@ -71,6 +71,17 @@ void mbed_start_application(uintptr_t address)
     powerdown_scb(address);
     mbed_mpu_free();
 
+#ifdef MBED_DEBUG
+    // Configs to make debugging easier
+#ifdef SCnSCB_ACTLR_DISDEFWBUF_Msk
+    // Disable write buffer to make BusFaults (eg write to ROM via NULL pointer) precise.
+    // Possible on Cortex-M3 and M4, not on M0, M7 or M33.
+    // Would be less necessary if ROM was write-protected in MPU to give a
+    // precise MemManage exception.
+    SCnSCB->ACTLR |= SCnSCB_ACTLR_DISDEFWBUF_Msk;
+#endif
+#endif
+
     sp = *((void **)address + 0);
     pc = *((void **)address + 1);
     start_new_application(sp, pc);