PIC32: add software reset support

The PIC32MX does not support the ejtag software reset - it is
optional in the ejtag spec.

We perform the equivalent using the microchip specific MTAP cmd's.
Signed-off-by: Spencer Oliver <ntfreak@users.sourceforge.net>

src/target/mips_ejtag.c

@@ -127,6 +127,37 @@ int mips_ejtag_drscan_32(struct mips_ejtag *ejtag_info, uint32_t *data)
 	return ERROR_OK;
 }
 
+int mips_ejtag_drscan_8(struct mips_ejtag *ejtag_info, uint32_t *data)
+{
+	struct jtag_tap *tap;
+	tap  = ejtag_info->tap;
+
+	if (tap == NULL)
+		return ERROR_FAIL;
+	struct scan_field field;
+	uint8_t t[4], r[4];
+	int retval;
+
+	field.num_bits = 8;
+	field.out_value = t;
+	buf_set_u32(field.out_value, 0, field.num_bits, *data);
+	field.in_value = r;
+
+	jtag_add_dr_scan(tap, 1, &field, jtag_get_end_state());
+
+	if ((retval = jtag_execute_queue()) != ERROR_OK)
+	{
+		LOG_ERROR("register read failed");
+		return retval;
+	}
+
+	*data = buf_get_u32(field.in_value, 0, 32);
+
+	keep_alive();
+
+	return ERROR_OK;
+}
+
 int mips_ejtag_step_enable(struct mips_ejtag *ejtag_info)
 {
 	static const uint32_t code[] = {

src/target/mips_ejtag.h

@@ -43,6 +43,11 @@
 /* microchip PIC32MX specific instructions */
 #define MTAP_SW_MTAP			0x04
 #define MTAP_SW_ETAP			0x05
+#define MTAP_COMMAND			0x07
+
+/* microchip specific cmds */
+#define MCHP_ASERT_RST			0xd1
+#define MCHP_DE_ASSERT_RST		0xd0
 
 /* ejtag control register bits ECR */
 #define EJTAG_CTRL_TOF			(1 << 1)
@@ -130,6 +135,7 @@ int mips_ejtag_exit_debug(struct mips_ejtag *ejtag_info);
 int mips_ejtag_get_impcode(struct mips_ejtag *ejtag_info, uint32_t *impcode);
 int mips_ejtag_get_idcode(struct mips_ejtag *ejtag_info, uint32_t *idcode);
 int mips_ejtag_drscan_32(struct mips_ejtag *ejtag_info, uint32_t *data);
+int mips_ejtag_drscan_8(struct mips_ejtag *ejtag_info, uint32_t *data);
 int mips_ejtag_fastdata_scan(struct mips_ejtag *ejtag_info, int write, uint32_t *data);
 
 int mips_ejtag_init(struct mips_ejtag *ejtag_info);

src/target/mips_m4k.c

@@ -250,11 +250,30 @@ int mips_m4k_assert_reset(struct target *target)
 	}
 	else
 	{
+		if (mips_m4k->is_pic32mx)
+		{
+			uint32_t mchip_cmd;
+
+			LOG_DEBUG("Using MTAP reset to reset processor...");
+
+			/* use microchip specific MTAP reset */
+			mips_ejtag_set_instr(ejtag_info, MTAP_SW_MTAP, NULL);
+			mips_ejtag_set_instr(ejtag_info, MTAP_COMMAND, NULL);
+
+			mchip_cmd = MCHP_ASERT_RST;
+			mips_ejtag_drscan_8(ejtag_info, &mchip_cmd);
+			mchip_cmd = MCHP_DE_ASSERT_RST;
+			mips_ejtag_drscan_8(ejtag_info, &mchip_cmd);
+			mips_ejtag_set_instr(ejtag_info, MTAP_SW_ETAP, NULL);
+		}
+		else
+		{
 			/* use ejtag reset - not supported by all cores */
 			uint32_t ejtag_ctrl = ejtag_info->ejtag_ctrl | EJTAG_CTRL_PRRST | EJTAG_CTRL_PERRST;
 			LOG_DEBUG("Using EJTAG reset (PRRST) to reset processor...");
 			mips_ejtag_set_instr(ejtag_info, EJTAG_INST_CONTROL, NULL);
 			mips_ejtag_drscan_32(ejtag_info, &ejtag_ctrl);
+		}
 	}
 
 	target->state = TARGET_RESET;
@@ -878,7 +897,7 @@ int mips_m4k_init_target(struct command_context *cmd_ctx, struct target *target)
 int mips_m4k_init_arch_info(struct target *target, struct mips_m4k_common *mips_m4k,
 		struct jtag_tap *tap)
 {
-	struct mips32_common *mips32 = &mips_m4k->mips32_common;
+	struct mips32_common *mips32 = &mips_m4k->mips32;
 
 	mips_m4k->common_magic = MIPSM4K_COMMON_MAGIC;
 
@@ -901,8 +920,8 @@ int mips_m4k_target_create(struct target *target, Jim_Interp *interp)
 int mips_m4k_examine(struct target *target)
 {
 	int retval;
-	struct mips32_common *mips32 = target_to_mips32(target);
-	struct mips_ejtag *ejtag_info = &mips32->ejtag_info;
+	struct mips_m4k_common *mips_m4k = target_to_m4k(target);
+	struct mips_ejtag *ejtag_info = &mips_m4k->mips32.ejtag_info;
 	uint32_t idcode = 0;
 
 	if (!target_was_examined(target))
@@ -916,6 +935,7 @@ int mips_m4k_examine(struct target *target)
 			 * as it is not selected by default */
 			mips_ejtag_set_instr(ejtag_info, MTAP_SW_ETAP, NULL);
 			LOG_DEBUG("PIC32MX Detected - using EJTAG Interface");
+			mips_m4k->is_pic32mx = true;
 		}
 	}
 

src/target/mips_m4k.h

@@ -32,6 +32,7 @@ struct target;
 struct mips_m4k_common
 {
 	int common_magic;
+	bool is_pic32mx;
 	struct mips32_common mips32;
 };