target/riscv: reset delays during batch scans

This commit is related to testing how OpenOCD responds to `dmi.busy`.

Consider testing on Spike (e.g. `riscv-tests/debug` testsuite). Spike
returns `dmi.busy` if there were less then a given number of RTI cycles
(`required_rti_cycles`) between DR_UPDATE and DR_CAPTURE:
https://github.com/riscv-software-src/riscv-isa-sim/blob/master/riscv/jtag_dtm.cc#L145
https://github.com/riscv-software-src/riscv-isa-sim/blob/master/riscv/jtag_dtm.cc#L202
`required_rti_cycles` gets it's value from `--dmi-rti` CLI argument and
is constant throughout the run.

OpenOCD learns this required number of RTI cycles by starting with zero
and increasing it if `dmi.busy` is encountered. So the required number
of RTI cycles is learned during the first DMI access in the `examine()`.

To induce `dmi.busy` on demand `riscv reset_delays <x>` command is
provided. This command initializes `riscv_info::reset_delays_wait`
counter to the provided `<x>` value. The counter is decreased before a
DMI access and when it reaches zero the learned value of RTI cycles
required is reset, so the DMI access results in `dmi.busy`.

Now consider running a batch of accesses.  Before the change all the
accesses in the batch had the same number of RIT cycles in between them.
So either:
* Number of accesses in the batch was greater then the value of
  `riscv_info::reset_delays_wait` counter and there was no `dmi.busy`
throughout the batch.
* Number of accesses in the batch was less or equal then the value of
  `riscv_info::reset_delays_wait` counter and the first access of the
batch resulted in `dmi.busy`.

Therefore it was impossible to encounter `dmi.busy` on any scan of the
batch except the first one.

Change-Id: Ib0714ecaf7d2e11878140d16d9aa6152ff20f1e9
Signed-off-by: Evgeniy Naydanov <evgeniy.naydanov@syntacore.com>

src/target/riscv/batch.c

@@ -89,7 +89,8 @@ bool riscv_batch_full(struct riscv_batch *batch)
 	return riscv_batch_available_scans(batch) == 0;
 }
 
-int riscv_batch_run(struct riscv_batch *batch)
+int riscv_batch_run(struct riscv_batch *batch, bool resets_delays,
+		size_t reset_delays_after)
 {
 	if (batch->used_scans == 0) {
 		LOG_TARGET_DEBUG(batch->target, "Ignoring empty batch.");
@@ -104,7 +105,9 @@ int riscv_batch_run(struct riscv_batch *batch)
 		else
 			jtag_add_dr_scan(batch->target->tap, 1, batch->fields + i, TAP_IDLE);
 
-		if (batch->idle_count > 0)
+		const bool delays_were_reset = resets_delays
+			&& (i >= reset_delays_after);
+		if (batch->idle_count > 0 && !delays_were_reset)
 			jtag_add_runtest(batch->idle_count, TAP_IDLE);
 	}
 

src/target/riscv/batch.h

@@ -55,8 +55,15 @@ void riscv_batch_free(struct riscv_batch *batch);
 /* Checks to see if this batch is full. */
 bool riscv_batch_full(struct riscv_batch *batch);
 
-/* Executes this scan batch. */
-int riscv_batch_run(struct riscv_batch *batch);
+/* Executes this batch of JTAG DTM DMI scans.
+ *
+ * If resets_delays is true, the algorithm will stop inserting idle cycles
+ * (JTAG Run-Test Idle) after "reset_delays_after" number of scans is
+ * performed.  This is useful for stress-testing of RISC-V algorithms in
+ * OpenOCD that are based on batches.
+ */
+int riscv_batch_run(struct riscv_batch *batch, bool resets_delays,
+		size_t reset_delays_after);
 
 /* Adds a DM register write to this batch. */
 void riscv_batch_add_dm_write(struct riscv_batch *batch, uint64_t address, uint32_t data,

src/target/riscv/riscv-013.c

@@ -496,6 +496,24 @@ static void increase_dmi_busy_delay(struct target *target)
 	dtmcontrol_scan(target, DTM_DTMCS_DMIRESET, NULL /* discard result */);
 }
 
+static void decrement_reset_delays_counter(struct target *target, size_t finished_scans)
+{
+	RISCV_INFO(r);
+	if (r->reset_delays_wait < 0) {
+		assert(r->reset_delays_wait == -1);
+		return;
+	}
+	if ((size_t)r->reset_delays_wait >= finished_scans) {
+		r->reset_delays_wait -= finished_scans;
+		return;
+	}
+	r->reset_delays_wait = -1;
+	LOG_TARGET_DEBUG(target,
+			"resetting learned delays (reset_delays_wait counter expired)");
+	RISCV013_INFO(info);
+	info->dmi_busy_delay = 0;
+	info->ac_busy_delay = 0;
+}
 /**
  * exec: If this is set, assume the scan results in an execution, so more
  * run-test/idle cycles may be required.
@@ -505,7 +523,6 @@ static dmi_status_t dmi_scan(struct target *target, uint32_t *address_in,
 		bool exec)
 {
 	riscv013_info_t *info = get_info(target);
-	RISCV_INFO(r);
 	unsigned num_bits = info->abits + DTM_DMI_OP_LENGTH + DTM_DMI_DATA_LENGTH;
 	size_t num_bytes = (num_bits + 7) / 8;
 	uint8_t in[num_bytes];
@@ -517,14 +534,7 @@ static dmi_status_t dmi_scan(struct target *target, uint32_t *address_in,
 	};
 	riscv_bscan_tunneled_scan_context_t bscan_ctxt;
 
-	if (r->reset_delays_wait >= 0) {
-		r->reset_delays_wait--;
-		if (r->reset_delays_wait < 0) {
-			LOG_TARGET_DEBUG(target, "reset_delays_wait done");
-			info->dmi_busy_delay = 0;
-			info->ac_busy_delay = 0;
-		}
-	}
+	decrement_reset_delays_counter(target, 1);
 
 	memset(in, 0, num_bytes);
 	memset(out, 0, num_bytes);
@@ -2617,19 +2627,16 @@ static int sb_write_address(struct target *target, target_addr_t address,
 		(uint32_t)address, false, ensure_success);
 }
 
-static int batch_run(const struct target *target, struct riscv_batch *batch)
+static int batch_run(struct target *target, struct riscv_batch *batch)
 {
-	RISCV013_INFO(info);
 	RISCV_INFO(r);
-	if (r->reset_delays_wait >= 0) {
-		r->reset_delays_wait -= batch->used_scans;
-		if (r->reset_delays_wait <= 0) {
-			batch->idle_count = 0;
-			info->dmi_busy_delay = 0;
-			info->ac_busy_delay = 0;
-		}
-	}
-	return riscv_batch_run(batch);
+	const int result = riscv_batch_run(batch, /*resets_delays*/  r->reset_delays_wait >= 0,
+			r->reset_delays_wait);
+	/* TODO: `finished_scans` should be the number of scans that have
+	 * finished, not the number of scans scheduled. */
+	const size_t finished_scans = batch->used_scans;
+	decrement_reset_delays_counter(target, finished_scans);
+	return result;
 }
 
 static int sba_supports_access(struct target *target, unsigned int size_bytes)

src/target/riscv/riscv.c

@@ -450,6 +450,7 @@ static int riscv_init_target(struct command_context *cmd_ctx,
 	LOG_TARGET_DEBUG(target, "riscv_init_target()");
 	RISCV_INFO(info);
 	info->cmd_ctx = cmd_ctx;
+	info->reset_delays_wait = -1;
 
 	select_dtmcontrol.num_bits = target->tap->ir_length;
 	select_dbus.num_bits = target->tap->ir_length;
@@ -3850,10 +3851,8 @@ COMMAND_HANDLER(riscv_reset_delays)
 {
 	int wait = 0;
 
-	if (CMD_ARGC > 1) {
-		LOG_ERROR("Command takes at most one argument");
+	if (CMD_ARGC > 1)
 		return ERROR_COMMAND_SYNTAX_ERROR;
-	}
 
 	if (CMD_ARGC == 1)
 		COMMAND_PARSE_NUMBER(int, CMD_ARGV[0], wait);
@@ -6455,7 +6454,7 @@ int riscv_init_registers(struct target *target)
 	return ERROR_OK;
 }
 
-void riscv_add_bscan_tunneled_scan(struct target *target, struct scan_field *field,
+void riscv_add_bscan_tunneled_scan(struct target *target, const struct scan_field *field,
 					riscv_bscan_tunneled_scan_context_t *ctxt)
 {
 	jtag_add_ir_scan(target->tap, &select_user4, TAP_IDLE);

src/target/riscv/riscv.h

@@ -454,7 +454,7 @@ void riscv_semihosting_init(struct target *target);
 
 enum semihosting_result riscv_semihosting(struct target *target, int *retval);
 
-void riscv_add_bscan_tunneled_scan(struct target *target, struct scan_field *field,
+void riscv_add_bscan_tunneled_scan(struct target *target, const struct scan_field *field,
 		riscv_bscan_tunneled_scan_context_t *ctxt);
 
 int riscv_read_by_any_size(struct target *target, target_addr_t address, uint32_t size, uint8_t *buffer);