From 9c028895aa8a6ae1a26e2b9d87f6a9675b97434a Mon Sep 17 00:00:00 2001
From: Keith Packard <keithp@keithp.com>
Date: Mon, 7 May 2018 13:06:03 -0700
Subject: Video timing measurement tool

Uses a device that signals whether it sees white or black over USB to
measure accuracy of frame timing reports.

Signed-off-by: Keith Packard <keithp@keithp.com>
---
 Makefile  |   7 +++
 vidtime.c | 146 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 153 insertions(+)
 create mode 100644 Makefile
 create mode 100644 vidtime.c

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..65acc36
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,7 @@
+SRCS=vidtime.c
+OBJS=$(SRCS:.c=.o)
+LIBS=-lX11 -lpthread
+CFLAGS=-O0 -g
+
+vidtime: $(OBJS)
+	$(CC) $(CFLAGS) -o $@ $(OBJS) $(LIBS)
diff --git a/vidtime.c b/vidtime.c
new file mode 100644
index 0000000..59cabf7
--- /dev/null
+++ b/vidtime.c
@@ -0,0 +1,146 @@
+/*
+ * Copyright © 2018 Keith Packard <keithp@keithp.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+
+#include <X11/Xlib.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <stddef.h>
+#include <stdbool.h>
+#include <time.h>
+#include <pthread.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/ioctl.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <termios.h>
+
+struct monitor {
+	int	fd;
+};
+
+static uint64_t vid_clock(void)
+{
+	struct timespec	ts;
+	clock_gettime(CLOCK_REALTIME, &ts);
+	return ((uint64_t) ts.tv_sec * 1000000000ULL + (uint64_t) ts.tv_nsec);
+}
+
+static void flush(int fd)
+{
+	char	buf[1024];
+	int	n;
+	int	avail;
+	for (;;) {
+		n = ioctl(fd, FIONREAD, &avail);
+		if (n < 0 || avail <= 0)
+			break;
+		read(fd, buf, avail);
+	}
+}
+
+static uint64_t		vid_time[2];
+
+static pthread_mutex_t	time_mutex = PTHREAD_MUTEX_INITIALIZER;
+static pthread_cond_t	time_cond = PTHREAD_COND_INITIALIZER;
+
+
+static void *monitor_device(void *arg)
+{
+	struct monitor	*m = arg;
+	int	fd = m->fd;
+	char	buf[256];
+	int	n;
+	struct termios	termios;
+	uint64_t	t;
+
+	tcgetattr(fd, &termios);
+	cfmakeraw(&termios);
+	cfsetospeed(&termios, B9600);
+	cfsetispeed(&termios, B9600);
+	tcsetattr(fd, TCSAFLUSH, &termios);
+	flush(fd);
+	write(fd, "E 0\nV 0\n", 8);
+	sleep(1);
+	flush(fd);
+	write(fd, "V 1\n", 4);
+	for (;;) {
+		n = read(fd, buf, sizeof(buf));
+		if (n < 0) {
+			perror("read");
+			return NULL;
+		}
+		t = vid_clock();
+		switch(buf[0]) {
+		case '1':
+		case '0':
+			pthread_mutex_lock(&time_mutex);
+			vid_time[buf[0] - '0'] = t;
+			pthread_cond_signal(&time_cond);
+			pthread_mutex_unlock(&time_mutex);
+			break;
+		}
+	}
+}
+
+#define W	512
+#define H	512
+#define DEV	"/dev/ttyACM0"
+
+int main(int argc, char **argv)
+{
+	Display	*dpy;
+	int	scr;
+	Window	root;
+	Window	w;
+	GC	gc;
+	Pixmap	pix;
+	int	v = 0;
+	struct timespec	ts = { .tv_sec = 1, .tv_nsec = 0 };
+	pthread_t	monitor_thread;
+	struct monitor	monitor;
+	uint64_t	put, got;
+
+	monitor.fd = open(DEV, O_RDWR);
+	if (monitor.fd < 0) {
+		perror(DEV);
+		exit(1);
+	}
+	pthread_create(&monitor_thread, NULL, monitor_device, &monitor);
+
+	dpy = XOpenDisplay(NULL);
+	scr = DefaultScreen(dpy);
+	root = RootWindow(dpy, scr);
+	w = XCreateSimpleWindow(dpy, root, 0, 0, W, H, 0, 0, 0);
+	gc = XCreateGC(dpy, w, 0, NULL);
+	XMapWindow(dpy, w);
+	for (;;) {
+		XSetForeground(dpy, gc, v ? WhitePixel(dpy, scr) : BlackPixel(dpy, scr));
+		XFillRectangle(dpy, w, gc, 0, 0, W, H);
+		put = vid_clock();
+		XFlush(dpy);
+		pthread_mutex_lock(&time_mutex);
+		for (;;) {
+			if (vid_time[v] > put) {
+				got = vid_time[v];
+				break;
+			}
+			pthread_cond_wait (&time_cond, &time_mutex);
+		}
+		pthread_mutex_unlock(&time_mutex);
+		printf("delay %f\n", (got - put) / 1e9);
+		v = 1-v;
+	}
+}
-- 
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