From: Delio Brignoli <brignoli.delio@gmail.com>
Date: Fri, 20 Oct 2017 09:22:45 +0000 (+0200)
Subject: modify avr_callback_sleep_raw() to mitigate sim time and wall clock time divergence
X-Git-Tag: v1.6~4
X-Git-Url: https://git.htl-mechatronik.at/public/?a=commitdiff_plain;h=6660aba00a898ff4db6c689e35e7fd03b4f9d47d;p=sx%2Fsimavr.git

modify avr_callback_sleep_raw() to mitigate sim time and wall clock time divergence

To avoid simulated time and wall clock time to diverge over time
this implementation tries to keep them in sync (roughly) by sleeping
for the time required to match the expected sleep deadline
in wall clock time.

The simulation will burst as fast as the host CPU will allow
until the simulated MCU sleeps, at which point avr_callback_sleep_raw()
sleeps for the time required to sync wall clock time with simulated MCU
time.
---

diff --git a/simavr/sim/sim_avr.c b/simavr/sim/sim_avr.c
index 9999a17..6106df6 100644
--- a/simavr/sim/sim_avr.c
+++ b/simavr/sim/sim_avr.c
@@ -23,6 +23,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <time.h>
 #include <unistd.h>
 #include "sim_avr.h"
 #include "sim_core.h"
@@ -148,6 +149,10 @@ avr_reset(
 		avr->sreg[i] = 0;
 	avr_interrupt_reset(avr);
 	avr_cycle_timer_reset(avr);
+	/* Take simulation start time */
+	struct timespec tp;
+	clock_gettime(CLOCK_MONOTONIC_RAW, &tp);
+	avr->sim_start_time_ns = tp.tv_sec*1E9+tp.tv_nsec;
 	if (avr->reset)
 		avr->reset(avr);
 	avr_io_t * port = avr->io_port;
@@ -311,15 +316,30 @@ avr_callback_run_gdb(
 
 }
 
+/*
+To avoid simulated time and wall clock time to diverge over time
+this function tries to keep them in sync (roughly) by sleeping
+for the time required to match the expected sleep deadline
+in wall clock time.
+*/
 void
 avr_callback_sleep_raw(
-		avr_t * avr,
-		avr_cycle_count_t howLong)
+		avr_t *avr,
+		avr_cycle_count_t how_long)
 {
-	uint32_t usec = avr_pending_sleep_usec(avr, howLong);
-	if (usec > 0) {
-		usleep(usec);
+	struct timespec tp;
+
+	/* figure out how long we should wait to match the sleep deadline */
+	uint64_t deadline_ns = avr_cycles_to_nsec(avr, avr->cycle + how_long);
+	clock_gettime(CLOCK_MONOTONIC_RAW, &tp);
+	uint64_t runtime_ns = (tp.tv_sec*1E9+tp.tv_nsec) - avr->sim_start_time_ns;
+	if (runtime_ns >= deadline_ns) {
+		return;
 	}
+
+	uint64_t sleep_us = (deadline_ns - runtime_ns)/1000;
+	usleep(sleep_us);
+	return;
 }
 
 void
diff --git a/simavr/sim/sim_avr.h b/simavr/sim/sim_avr.h
index aedffb2..92459dc 100644
--- a/simavr/sim/sim_avr.h
+++ b/simavr/sim/sim_avr.h
@@ -201,6 +201,7 @@ typedef struct avr_t {
 	 * is passed on to the operating system.
 	 */
 	uint32_t 			sleep_usec;
+	uint64_t			sim_start_time_ns;
 
 	// called at init time
 	void (*init)(struct avr_t * avr);