ETM: add "etm trigger_debug" command

In conjunction with manual register setup, this lets the ETM trigger
cause entry to debug state.   It should make it easier to test and
bugfix the ETM code, by enabling non-trace usage and isolating bugs
specific to thef ETM support.  (One current issue being that trace
data collection using the ETB doesn't yet behave.)

For example, many ARM9 cores with an ETM should be able to implement
four more (simple) breakpoints and two more (simple) watchpoints than
the EmbeddedICE supports.  Or, they should be able to support complex
breakpoints, incorporating ETM sequencer, counters, and/or subroutine
entry/exit criteria int criteria used to trigger debug entry.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>

NEWS

@@ -34,6 +34,7 @@ Target Layer:
 		- Exposed DWT registers like cycle counter
 	ETM, ETB
 		- "trigger_percent" command moved ETM --> ETB
+		- "etm trigger_debug" command added
 
 Flash Layer:
 	'flash bank' and 'nand device' take <bank_name> as first argument.

doc/openocd.texi

@@ -5512,6 +5512,17 @@ trace stream without an image of the code.
 @end itemize
 @end deffn
 
+@deffn Command {etm trigger_debug} (@option{enable}|@option{disable})
+Displays whether ETM triggering debug entry (like a breakpoint) is
+enabled or disabled, after optionally modifying that configuration.
+The default behaviour is @option{disable}.
+Any change takes effect after the next @command{etm start}.
+
+By using script commands to configure ETM registers, you can make the
+processor enter debug state automatically when certain conditions,
+more complex than supported by the breakpoint hardware, happen.
+@end deffn
+
 @subsection ETM Trace Operation
 
 After setting up the ETM, you can use it to collect data.

src/target/etm.c

@@ -446,12 +446,15 @@ int etm_setup(struct target *target)
 	etm_ctrl_value = (etm_ctrl_value
 			& ~ETM_PORT_WIDTH_MASK
 			& ~ETM_PORT_MODE_MASK
+			& ~ETM_CTRL_DBGRQ
 			& ~ETM_PORT_CLOCK_MASK)
 		| etm_ctx->control;
 
 	buf_set_u32(etm_ctrl_reg->value, 0, 32, etm_ctrl_value);
 	etm_store_reg(etm_ctrl_reg);
 
+	etm_ctx->control = etm_ctrl_value;
+
 	if ((retval = jtag_execute_queue()) != ERROR_OK)
 		return retval;
 
@@ -1338,8 +1341,6 @@ COMMAND_HANDLER(handle_etm_tracemode_command)
 		if (!etm_ctrl_reg)
 			return ERROR_FAIL;
 
-		etm_get_reg(etm_ctrl_reg);
-
 		etm->control &= ~TRACEMODE_MASK;
 		etm->control |= tracemode & TRACEMODE_MASK;
 
@@ -2016,6 +2017,56 @@ COMMAND_HANDLER(handle_etm_stop_command)
 	return ERROR_OK;
 }
 
+COMMAND_HANDLER(handle_etm_trigger_debug_command)
+{
+	struct target *target;
+	struct arm *arm;
+	struct etm_context *etm;
+
+	target = get_current_target(CMD_CTX);
+	arm = target_to_arm(target);
+	if (!is_arm(arm))
+	{
+		command_print(CMD_CTX, "ETM: %s isn't an ARM",
+				target_name(target));
+		return ERROR_FAIL;
+	}
+
+	etm = arm->etm;
+	if (!etm)
+	{
+		command_print(CMD_CTX, "ETM: no ETM configured for %s",
+				target_name(target));
+		return ERROR_FAIL;
+	}
+
+	if (CMD_ARGC == 1) {
+		struct reg *etm_ctrl_reg;
+		bool dbgrq;
+
+		etm_ctrl_reg = etm_reg_lookup(etm, ETM_CTRL);
+		if (!etm_ctrl_reg)
+			return ERROR_FAIL;
+
+		COMMAND_PARSE_ENABLE(CMD_ARGV[0], dbgrq);
+		if (dbgrq)
+			etm->control |= ETM_CTRL_DBGRQ;
+		else
+			etm->control &= ~ETM_CTRL_DBGRQ;
+
+		/* etm->control will be written to hardware
+		 * the next time an "etm start" is issued.
+		 */
+		buf_set_u32(etm_ctrl_reg->value, 0, 32, etm->control);
+	}
+
+	command_print(CMD_CTX, "ETM: %s debug halt",
+			(etm->control & ETM_CTRL_DBGRQ)
+				? "triggers"
+				: "does not trigger");
+	return ERROR_OK;
+}
+
 COMMAND_HANDLER(handle_etm_analyze_command)
 {
 	struct target *target;
@@ -2112,10 +2163,17 @@ static const struct command_registration etm_exec_command_handlers[] = {
 		.help = "stop ETM trace collection",
 	},
 	{
-		.name = "analyze",
+		.name = "trigger_debug",
-		.handler = &handle_etm_analyze_command,
+		.handler = handle_etm_trigger_debug_command,
 		.mode = COMMAND_EXEC,
-		.help = "anaylze collected ETM trace",
+		.help = "enable/disable debug entry on trigger",
+		.usage = "(enable | disable)",
+	},
+	{
+		.name = "analyze",
+		.handler = handle_etm_analyze_command,
+		.mode = COMMAND_EXEC,
+		.help = "analyze collected ETM trace",
 	},
 	{
 		.name = "image",