target: if polling fails, back off

back-off algorithm for polling. Double polling
interval up to 5000ms when it fails.

when polling succeeds, reset backoff.

This avoids flooding logs(as much) when working
with conditions where the target polling will fail.

Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>

1 files changed, 29 insertions, 8 deletions

diff --git a/src/target/target.c b/src/target/target.c
index f178ae36..d7607e3a 100644
--- a/src/target/target.c
+++ b/src/target/target.c
@@ -96,6 +96,7 @@ static struct target_type *target_types[] =
 struct target *all_targets = NULL;
 static struct target_event_callback *target_event_callbacks = NULL;
 static struct target_timer_callback *target_timer_callbacks = NULL;
+static const int polling_interval = 100;
 
 static const Jim_Nvp nvp_assert[] = {
 	{ .name = "assert", NVP_ASSERT },
@@ -862,7 +863,7 @@ static int target_init(struct command_context *cmd_ctx)
 		return retval;
 
 	retval = target_register_timer_callback(&handle_target,
-			100, 1, cmd_ctx->interp);
+			polling_interval, 1, cmd_ctx->interp);
 	if (ERROR_OK != retval)
 		return retval;
 
@@ -1800,6 +1801,9 @@ static int sense_handler(void)
 	return ERROR_OK;
 }
 
+static int backoff_times = 0;
+static int backoff_count = 0;
+
 /* process target state changes */
 static int handle_target(void *priv)
 {
@@ -1862,6 +1866,14 @@ static int handle_target(void *priv)
 		recursive = 0;
 	}
 
+	if (backoff_times > backoff_count)
+	{
+		/* do not poll this time as we failed previously */
+		backoff_count++;
+		return ERROR_OK;
+	}
+	backoff_count = 0;
+
 	/* Poll targets for state changes unless that's globally disabled.
 	 * Skip targets that are currently disabled.
 	 */
@@ -1878,17 +1890,26 @@ static int handle_target(void *priv)
 			/* polling may fail silently until the target has been examined */
 			if ((retval = target_poll(target)) != ERROR_OK)
 			{
-				/* FIX!!!!! If we add a LOG_INFO() here to output a line in GDB
-				 * *why* we are aborting GDB, then we'll spam telnet when the
-				 * poll is failing persistently.
-				 *
-				 * If we could implement an event that detected the
-				 * target going from non-pollable to pollable, we could issue
-				 * an error only upon the transition.
+				/* 100ms polling interval. Increase interval between polling up to 5000ms */
+				if (backoff_times * polling_interval < 5000)
+				{
+					backoff_times *= 2;
+					backoff_times++;
+				}
+				LOG_USER("Polling target failed, GDB will be halted. Polling again in %dms", backoff_times * polling_interval);
+
+				/* Tell GDB to halt the debugger. This allows the user to
+				 * run monitor commands to handle the situation.
 				 */
 				target_call_event_callbacks(target, TARGET_EVENT_GDB_HALT);
 				return retval;
 			}
+			/* Since we succeeded, we reset backoff count */
+			if (backoff_times > 0)
+			{
+				LOG_USER("Polling succeeded again");
+			}
+			backoff_times = 0;
 		}
 	}