From cda7487cbe676e5d896ddf183a04f41e899f3f7a Mon Sep 17 00:00:00 2001
From: geeksville <kevinh@geeksville.com>
Date: Sun, 24 May 2020 16:08:58 -0700
Subject: [PATCH] add a NRF52 hardfault handler

---
 .vscode/settings.json       |  3 ++
 docs/software/nrf52-TODO.md |  2 +-
 src/nrf52/hardfault.cpp     | 78 +++++++++++++++++++++++++++++++++++++
 3 files changed, 82 insertions(+), 1 deletion(-)
 create mode 100644 src/nrf52/hardfault.cpp

diff --git a/.vscode/settings.json b/.vscode/settings.json
index 62c6cdf0f..aebb3d4a5 100644
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -51,9 +51,12 @@
     },
     "cSpell.words": [
         "Blox",
+        "HFSR",
         "Meshtastic",
         "NEMAGPS",
         "Ublox",
+        "bkpt",
+        "cfsr",
         "descs",
         "ocrypto",
         "protobufs"
diff --git a/docs/software/nrf52-TODO.md b/docs/software/nrf52-TODO.md
index 47df1ef5b..e48320ae7 100644
--- a/docs/software/nrf52-TODO.md
+++ b/docs/software/nrf52-TODO.md
@@ -7,7 +7,7 @@
 Minimum items needed to make sure hardware is good.
 
 - find out why we reboot while  debugging
-- install a hardfault handler for null ptrs (if one isn't already installed)
+- DONE install a hardfault handler for null ptrs (if one isn't already installed)
 - test my hackedup bootloader on the real hardware
 - Use the PMU driver on real hardware
 - Use new radio driver on real hardware
diff --git a/src/nrf52/hardfault.cpp b/src/nrf52/hardfault.cpp
new file mode 100644
index 000000000..4cf4dff79
--- /dev/null
+++ b/src/nrf52/hardfault.cpp
@@ -0,0 +1,78 @@
+#include "configuration.h"
+#include <core_cm4.h>
+
+// Based on reading/modifying https://blog.feabhas.com/2013/02/developing-a-generic-hard-fault-handler-for-arm-cortex-m3cortex-m4/
+
+enum { r0, r1, r2, r3, r12, lr, pc, psr };
+
+// Per http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0552a/Cihcfefj.html
+static void printUsageErrorMsg(uint32_t cfsr)
+{
+    DEBUG_MSG("Usage fault: ");
+    cfsr >>= SCB_CFSR_USGFAULTSR_Pos; // right shift to lsb
+    if ((cfsr & (1 << 9)) != 0)
+        DEBUG_MSG("Divide by zero\n");
+    if ((cfsr & (1 << 8)) != 0)
+        DEBUG_MSG("Unaligned\n");
+}
+
+static void printBusErrorMsg(uint32_t cfsr)
+{
+    DEBUG_MSG("Usage fault: ");
+    cfsr >>= SCB_CFSR_BUSFAULTSR_Pos; // right shift to lsb
+    if ((cfsr & (1 << 0)) != 0)
+        DEBUG_MSG("Instruction bus error\n");
+    if ((cfsr & (1 << 1)) != 0)
+        DEBUG_MSG("Precise data bus error\n");
+    if ((cfsr & (1 << 2)) != 0)
+        DEBUG_MSG("Imprecise data bus error\n");
+}
+
+static void printMemErrorMsg(uint32_t cfsr)
+{
+    DEBUG_MSG("Usage fault: ");
+    cfsr >>= SCB_CFSR_MEMFAULTSR_Pos; // right shift to lsb
+    if ((cfsr & (1 << 0)) != 0)
+        DEBUG_MSG("Instruction access violation\n");
+    if ((cfsr & (1 << 1)) != 0)
+        DEBUG_MSG("Data access violation\n");
+}
+
+static void HardFault_Impl(uint32_t stack[])
+{
+    DEBUG_MSG("In Hard Fault Handler\n");
+    DEBUG_MSG("SCB->HFSR = 0x%08lx\n", SCB->HFSR);
+
+    if ((SCB->HFSR & SCB_HFSR_FORCED_Msk) != 0) {
+        DEBUG_MSG("Forced Hard Fault\n");
+        DEBUG_MSG("SCB->CFSR = 0x%08lx\n", SCB->CFSR);
+
+        if ((SCB->CFSR & SCB_CFSR_USGFAULTSR_Msk) != 0) {
+            printUsageErrorMsg(SCB->CFSR);
+        }
+        if ((SCB->CFSR & SCB_CFSR_BUSFAULTSR_Msk) != 0) {
+            printBusErrorMsg(SCB->CFSR);
+        }
+        if ((SCB->CFSR & SCB_CFSR_MEMFAULTSR_Msk) != 0) {
+            printMemErrorMsg(SCB->CFSR);
+        }
+
+        DEBUG_MSG("r0  = 0x%08lx\n", stack[r0]);
+        DEBUG_MSG("r1  = 0x%08lx\n", stack[r1]);
+        DEBUG_MSG("r2  = 0x%08lx\n", stack[r2]);
+        DEBUG_MSG("r3  = 0x%08lx\n", stack[r3]);
+        DEBUG_MSG("r12 = 0x%08lx\n", stack[r12]);
+        DEBUG_MSG("lr  = 0x%08lx\n", stack[lr]);
+        DEBUG_MSG("pc  = 0x%08lx\n", stack[pc]);
+        DEBUG_MSG("psr = 0x%08lx\n", stack[psr]);
+        asm volatile("bkpt #01");
+        while (1)
+            ;
+    }
+}
+
+void HardFault_Handler(void)
+{
+    asm volatile(" mrs r0,msp\n"
+                 " b HardFault_Impl \n");
+}