fix software reset by writing in SYSRESETQ register when a reset is r…

…equested (#73)

Some debugger software (e.g. Keil) does not perform a software reset when
resetting the target. When this option enabled, a soft reset is attempted
when DAP_ResetTarget() is performed. This is done by writing to the
SYSRESETREQ field of the AIRCR register in the Cortex-M architecture.

This should work for ARMv6-m, ARMv7-m and ARMv8-m architecture. However,
there is no guarantee that the reset operation will be executed correctly.

Only available for SWD.

Links: #73
---------

Co-authored-by: windowsair <msdn_02@sina.com>

components/DAP/source/DAP.c

@@ -273,6 +273,22 @@ static uint32_t DAP_Disconnect(uint8_t *response) {
 //   return:   number of bytes in response
 static uint32_t DAP_ResetTarget(uint8_t *response) {
 
+#if (USE_FORCE_SYSRESETREQ_AFTER_FLASH)
+  if (DAP_Data.debug_port == DAP_PORT_SWD) {
+    /* Workaround for software reset when nRESET is not connected */
+    uint8_t ack;
+    uint32_t AIRCR_REG_ADDR = 0xE000ED0C;
+    uint32_t AIRCR_RESET_VAL = 0x05FA << 16 | 1 << 2; /* Vector key | SYSRESETREQ bit */
+    uint8_t req = DAP_TRANSFER_APnDP | 0 | DAP_TRANSFER_A2 | 0;
+    ack = SWD_Transfer(req,&AIRCR_REG_ADDR);
+    if (ack == DAP_TRANSFER_OK) {
+      dap_os_delay(2);
+      req = DAP_TRANSFER_APnDP | 0 | DAP_TRANSFER_A2 | DAP_TRANSFER_A3;
+      SWD_Transfer(req,&AIRCR_RESET_VAL);
+    }
+  }
+#endif
+
   *(response+1) = RESET_TARGET();
   *(response+0) = DAP_OK;
   return (2U);
@@ -1850,4 +1866,4 @@ void DAP_Setup(void) {
 void dap_os_delay(int ms)
 {
   vTaskDelay(pdMS_TO_TICKS(ms));
-}
+}

main/dap_configuration.h

@@ -39,5 +39,20 @@
     #define DAP_PACKET_SIZE 255U // 255 for USB HID
 #endif
 
+/**
+ * @brief Enable this option to force a software reset when resetting the device
+ *
+ * Some debugger software (e.g. Keil) does not perform a software reset when
+ * resetting the target. When this option enabled, a soft reset is attempted
+ * when DAP_ResetTarget() is performed. This is done by writing to the
+ * SYSRESETREQ field of the AIRCR register in the Cortex-M architecture.
+ *
+ * This should work for ARMv6-m, ARMv7-m and ARMv8-m architecture. However,
+ * there is no guarantee that the reset operation will be executed correctly.
+ *
+ * Only available for SWD.
+ *
+ */
+#define USE_FORCE_SYSRESETREQ_AFTER_FLASH 0
 
 #endif