cortex_m3: add auto maskisr

This patch extends the cortex_m3 maskisr command by a new option 'auto'.
The 'auto' option handles interrupts during stepping in a way they are
processed but don't disturb the program flow during debugging.

Before one had to choose to either enable or disable interrupts. The former
steps into interrupt handlers when they trigger. This disturbs the flow during
debugging, making it hard to follow some piece of code when interrupts occur
often.

When interrupts are disabled, the flow isn't disturbed but code relying on
interrupt handlers to be processed will stop working. For example a delay
function counting the number of timer interrupts will never complete, RTOS
task switching will not occur and output I/O queues of interrupt driven
I/O will stall or overflow.

Using the 'maskisr' command also typically requires gdb hooks to be supplied
by the user to switch interrupts off during the step and to enable them again
afterward.

The new 'auto' option of the 'maskisr' command solves the above problems. When
set, the step command allows pending interrupt handlers to be executed before
the step, then the step is taken with interrupts disabled and finally interrupts
are enabled again. This way interrupt processing stays in the background without
disturbing the flow of debugging. No gdb hooks are required. The 'auto'
option is the default, since it's believed that handling interrupts in this
way is suitable for most users.

The principle used for interrupt handling could probably be used for other
targets too.

Signed-off-by: Spencer Oliver <ntfreak@users.sourceforge.net>

doc/openocd.texi

@@ -6720,8 +6720,21 @@ If @var{value} is defined, first assigns that.
 @subsection Cortex-M3 specific commands
 @cindex Cortex-M3
 
-@deffn Command {cortex_m3 maskisr} (@option{on}|@option{off})
+@deffn Command {cortex_m3 maskisr} (@option{auto}|@option{on}|@option{off})
 Control masking (disabling) interrupts during target step/resume.
+
+The @option{auto} option handles interrupts during stepping a way they get
+served but don't disturb the program flow. The step command first allows
+pending interrupt handlers to execute, then disables interrupts and steps over
+the next instruction where the core was halted. After the step interrupts
+are enabled again. If the interrupt handlers don't complete within 500ms,
+the step command leaves with the core running.
+
+Note that a free breakpoint is required for the @option{auto} option. If no
+breakpoint is available at the time of the step, then the step is taken
+with interrupts enabled, i.e. the same way the @option{off} option does.
+
+Default is @option{auto}.
 @end deffn
 
 @deffn Command {cortex_m3 vector_catch} [@option{all}|@option{none}|list]

src/target/cortex_m3.c

@@ -39,6 +39,7 @@
 #include "register.h"
 #include "arm_opcodes.h"
 #include "arm_semihosting.h"
+#include <helper/time_support.h>
 
 /* NOTE:  most of this should work fine for the Cortex-M1 and
  * Cortex-M0 cores too, although they're ARMv6-M not ARMv7-M.
@@ -858,6 +859,8 @@ static int cortex_m3_step(struct target *target, int current,
 	struct breakpoint *breakpoint = NULL;
 	struct reg *pc = armv7m->arm.pc;
 	bool bkpt_inst_found = false;
+	int retval;
+	bool isr_timed_out = false;
 
 	if (target->state != TARGET_HALTED)
 	{
@@ -891,11 +894,79 @@ static int cortex_m3_step(struct target *target, int current,
 	 * instruction - as such simulate a step */
 	if (bkpt_inst_found == false)
 	{
-		/* set step and clear halt */
-		cortex_m3_write_debug_halt_mask(target, C_STEP, C_HALT);
+		/* Automatic ISR masking mode off: Just step over the next instruction */
+		if ((cortex_m3->isrmasking_mode != CORTEX_M3_ISRMASK_AUTO))
+		{
+			cortex_m3_write_debug_halt_mask(target, C_STEP, C_HALT);
+		}
+		else
+		{
+			/* Process interrupts during stepping in a way they don't interfere
+			 * debugging.
+			 *
+			 * Principle:
+			 *
+			 * Set a temporary break point at the current pc and let the core run
+			 * with interrupts enabled. Pending interrupts get served and we run
+			 * into the breakpoint again afterwards. Then we step over the next
+			 * instruction with interrupts disabled.
+			 *
+			 * If the pending interrupts don't complete within time, we leave the
+			 * core running. This may happen if the interrupts trigger faster
+			 * than the core can process them or the handler doesn't return.
+			 *
+			 * If no more breakpoints are available we simply do a step with
+			 * interrupts enabled.
+			 *
+			 */
+
+			/* Set a temporary break point */
+			retval = breakpoint_add(target, pc_value , 2, BKPT_TYPE_BY_ADDR(pc_value));
+			bool tmp_bp_set = (retval == ERROR_OK);
+
+			/* No more breakpoints left, just do a step */
+			if (!tmp_bp_set)
+			{
+				cortex_m3_write_debug_halt_mask(target, C_STEP, C_HALT);
+			}
+			else
+			{
+				/* Start the core */
+				LOG_DEBUG("Starting core to serve pending interrupts");
+				int64_t t_start = timeval_ms();
+				cortex_m3_write_debug_halt_mask(target, 0, C_HALT | C_STEP);
+
+				/* Wait for pending handlers to complete or timeout */
+				do {
+					retval = mem_ap_read_atomic_u32(swjdp, DCB_DHCSR, &cortex_m3->dcb_dhcsr);
+					if (retval != ERROR_OK)
+					{
+						target->state = TARGET_UNKNOWN;
+						return retval;
+					}
+					isr_timed_out = ((timeval_ms() - t_start) > 500);
+				} while (!((cortex_m3->dcb_dhcsr & S_HALT) || isr_timed_out));
+
+				/* Remove the temporary breakpoint */
+				breakpoint_remove(target, pc_value);
+
+				if (isr_timed_out)
+				{
+					LOG_DEBUG("Interrupt handlers didn't complete within time, "
+							"leaving target running");
+				}
+				else
+				{
+					/* Step over next instruction with interrupts disabled */
+					cortex_m3_write_debug_halt_mask(target, C_HALT | C_MASKINTS, 0);
+					cortex_m3_write_debug_halt_mask(target, C_STEP, C_HALT);
+					/* Re-enable interrupts */
+					cortex_m3_write_debug_halt_mask(target, C_HALT, C_MASKINTS);
+				}
+			}
+		}
 	}
 
-	int retval;
 	retval = mem_ap_read_atomic_u32(swjdp, DCB_DHCSR, &cortex_m3->dcb_dhcsr);
 	if (retval != ERROR_OK)
 		return retval;
@@ -906,6 +977,13 @@ static int cortex_m3_step(struct target *target, int current,
 	if (breakpoint)
 		cortex_m3_set_breakpoint(target, breakpoint);
 
+	if (isr_timed_out) {
+		/* Leave the core running. The user has to stop execution manually. */
+		target->debug_reason = DBG_REASON_NOTHALTED;
+		target->state = TARGET_RUNNING;
+		return ERROR_OK;
+	}
+
 	LOG_DEBUG("target stepped dcb_dhcsr = 0x%" PRIx32
 			" nvic_icsr = 0x%" PRIx32,
 			cortex_m3->dcb_dhcsr, cortex_m3->nvic_icsr);
@@ -2104,6 +2182,15 @@ COMMAND_HANDLER(handle_cortex_m3_mask_interrupts_command)
 	struct cortex_m3_common *cortex_m3 = target_to_cm3(target);
 	int retval;
 
+	static const Jim_Nvp nvp_maskisr_modes[] = {
+		{ .name = "auto", .value = CORTEX_M3_ISRMASK_AUTO },
+		{ .name = "off" , .value = CORTEX_M3_ISRMASK_OFF },
+		{ .name = "on"  , .value = CORTEX_M3_ISRMASK_ON },
+		{ .name = NULL  , .value = -1 },
+	};
+	const Jim_Nvp *n;
+
+
 	retval = cortex_m3_verify_pointer(CMD_CTX, cortex_m3);
 	if (retval != ERROR_OK)
 		return retval;
@@ -2116,15 +2203,26 @@ COMMAND_HANDLER(handle_cortex_m3_mask_interrupts_command)
 
 	if (CMD_ARGC > 0)
 	{
-		bool enable;
-		COMMAND_PARSE_ON_OFF(CMD_ARGV[0], enable);
-		uint32_t mask_on = C_HALT | (enable ? C_MASKINTS : 0);
-		uint32_t mask_off = enable ? 0 : C_MASKINTS;
-		cortex_m3_write_debug_halt_mask(target, mask_on, mask_off);
+		n = Jim_Nvp_name2value_simple(nvp_maskisr_modes, CMD_ARGV[0]);
+		if (n->name == NULL)
+		{
+			return ERROR_COMMAND_SYNTAX_ERROR;
+		}
+		cortex_m3->isrmasking_mode = n->value;
+
+
+		if(cortex_m3->isrmasking_mode == CORTEX_M3_ISRMASK_ON)
+		{
+			cortex_m3_write_debug_halt_mask(target, C_HALT | C_MASKINTS, 0);
+		}
+		else
+		{
+			cortex_m3_write_debug_halt_mask(target, C_HALT, C_MASKINTS);
+		}
 	}
 
-	command_print(CMD_CTX, "cortex_m3 interrupt mask %s",
-			(cortex_m3->dcb_dhcsr & C_MASKINTS) ? "on" : "off");
+	n = Jim_Nvp_value2name_simple(nvp_maskisr_modes, cortex_m3->isrmasking_mode);
+	command_print(CMD_CTX, "cortex_m3 interrupt mask %s", n->name);
 
 	return ERROR_OK;
 }
@@ -2174,7 +2272,7 @@ static const struct command_registration cortex_m3_exec_command_handlers[] = {
 		.handler = handle_cortex_m3_mask_interrupts_command,
 		.mode = COMMAND_EXEC,
 		.help = "mask cortex_m3 interrupts",
-		.usage = "['on'|'off']",
+		.usage = "['auto'|'on'|'off']",
 	},
 	{
 		.name = "vector_catch",

src/target/cortex_m3.h

@@ -140,6 +140,13 @@ enum cortex_m3_soft_reset_config
 	CORTEX_M3_RESET_VECTRESET,
 };
 
+enum cortex_m3_isrmasking_mode
+{
+	CORTEX_M3_ISRMASK_AUTO,
+	CORTEX_M3_ISRMASK_OFF,
+	CORTEX_M3_ISRMASK_ON,
+};
+
 struct cortex_m3_common
 {
 	int common_magic;
@@ -166,6 +173,8 @@ struct cortex_m3_common
 
 	enum cortex_m3_soft_reset_config soft_reset_config;
 
+	enum cortex_m3_isrmasking_mode isrmasking_mode;
+
 	struct armv7m_common armv7m;
 };