Made communication with CNTR board more robust. Added documentation.

- cntr/README: description of the counter board and its application
- cntr/fw/common/crc32.c: variant of CRC32-IEEE802.3 shared by firmware and
  measurement application
- cntr/fw/cntr/ep0.c (my_setup), cntr/tools/cntr/cntr.c (get_sample):
  protect the counter value with a CRC and an one's complement copy
- cntr/fw/include/cntr/ep0.h: oops, wasn't checked into repository
- cntr/tools/cntr/cntr.c: added section titles
- cntr/tools/cntr/cntr.c (measure): show communication statistics at the end
- cntr/tools/cntr/cntr.c (measure, usage, main): new option -d to enable
  reporting of communication errors
- cntr/tools/cntr/cntr.c (set_stop, measure): let user stop measurement with
  SIGINT
- cntr/tools/cntr/cntr.c (measure): get multiple "first samples" and keep
  the one with the shortest round-trip time
- cntr/tools/cntr/cntr.c (measure): changed unit "ppk" (1/1000) to percent
  (1/100)
- cntr/tools/cntr/cntr.c (usage, main): command-line argument is now the
  accuracy goal, while the system clock deviation is set with the new
  option -c
- TODO: some more things to do

TODO

@@ -105,10 +105,30 @@ Things not done yet
 
 - measure duty cycle
 
-- display activity on clock input and duty cycle
+- use the LED to display activity on clock input and duty cycle
 
 - consider using a comparator and a DAC to allow for programmable logic levels
 
 - evaluate termination resistance
 
 - document circuit design
+
+- record beats between 16 bit counter polls and use them for the estimate
+  of lost cycles (2*1 is way too optimistic)
+
+- include system clock resolution in accuracy calculation
+
+- consider running shorter sliding windows to estimate drift
+
+- consider detecting unusual half-periods
+
+- consider using a reversed USB connector, to avoid having to cross D+/D- and,
+  worse, VBUS and GND
+
+- test input performance by counting a source that emits a known number of
+  cycles
+
+- consider using historical margins to sanity-check the current margin (if any
+  old.max < curr.min or old.min > curr.max, we have a problem) and to further
+  narrow the effective margin, thus achieving faster convergence. We would have
+  to consider temperature drift of the frequency source in this case.

cntr/README

@@ -0,0 +1,66 @@
+Arbitrary-precision counter
+===========================
+
+Theory of operation
+-------------------
+
+The arbitrary-precision counter counts clock cycles of a frequency
+source that is assumed to be free from drift. It compares the count
+with the host's system clock. If the system clock is synchronized with
+an accurate NTP reference, measurements with arbitrarily high accuracy
+can be obtained.
+
+In practice, this is limited by the the frequency source's drift and
+the time one is willing to wait. If NTP maintains the system time
+with an accuracy of +/- 100 ms, obtaining measurements with an
+accuracy of +/- 1 ppm would take about 28 hours.
+
+Additional error sources, such as the round-trip time when requesting
+a sample from the microcontroller, are also considered in the accuracy
+calculation.
+
+The counter consists of a board based on a C8051F320 microcontroller
+and the control software on the host. The microcontroller counts
+events in a free-running 16 bit counter that is regularly read and
+extended to 32 bits. The 32 bit counter is periodically queried by
+the host.
+
+The microcontroller's counter can count at a frequency of up to 3 MHz.
+(SYSCLK/4)
+
+In order to protect against transmission errors not detected by USB's
+CRC, which are occur relatively often, each packet is protected by a
+CRC-32 and an inverted copy of the payload. Corrupted packets are
+rejected by the host.
+
+The 32 bit counter wraps around at most once very 21.8 ms. The 32 bit
+counter wraps around at most every 1431 s. The host extends the 32 bit
+counter to 64 bits, and calculates frequency and accuracy from the
+count and the run time of the measurement application.
+
+
+Performing a measurement
+------------------------
+
+To perform a measurement, connect the CNTR board's probe input to the
+clock source and then run the "cntr" application on the host. An
+accuracy goal (in ppm) can be specified on the command line (see
+below).
+
+The host polls the microcontroller every 100 ms and displays the run
+time (in seconds), the measured frequency, and the accuracy achieved
+so far.
+
+Measurements can be stopped by pressing ^C or by specifying an
+accuracy goal. At the end, the total number of events counted and
+communication statistics are displayed.
+
+
+Updating the firmware
+---------------------
+
+The protocol revision and the build date of the firmware of the CNTR
+board can be queried with "cntr -i".
+
+To update the firmware, run
+cntr -r && sleep 1 && dfu-util -d 0x20b7:0xcb72 -D cntr.bin

cntr/fw/cntr/ep0.c

@@ -22,7 +22,6 @@
 #include "cntr/ep0.h"
 #include "version.h"
 
-
 #define debug(...)
 #define error(...)
 
@@ -61,9 +60,13 @@ static __xdata uint8_t buf[128];
 #define	BUILD_OFFSET	7	/* '#' plus "65535" plus ' ' */
 
 
+/* crc32() */
+#include "cntr/crc32.c"
+
+
 static __bit my_setup(struct setup_request *setup) __reentrant
 {
-	unsigned tmp;
+	uint32_t tmp;
 	uint8_t size, i;
 
 	switch (setup->bmRequestType | setup->bRequest << 8) {
@@ -102,7 +105,18 @@ static __bit my_setup(struct setup_request *setup) __reentrant
 		buf[1] = cntr[1];
 		buf[2] = cntr[2];
 		buf[3] = cntr[3];
-		usb_send(&ep0, buf, 4, NULL, NULL);
+		tmp = (uint32_t) buf[0] | ((uint32_t) buf[1] << 8) |
+		    ((uint32_t) buf[2] << 16) | ((uint32_t) buf[3] << 24);
+		tmp = crc32(tmp, 0xffffffff);
+		buf[4] = tmp;
+		buf[5] = tmp >> 8;
+		buf[6] = tmp >> 16;
+		buf[7] = tmp >> 24;
+		buf[8] = ~cntr[0];
+		buf[9] = ~cntr[1];
+		buf[10] = ~cntr[2];
+		buf[11] = ~cntr[3];
+		usb_send(&ep0, buf, 12, NULL, NULL);
 		return 1;
 
 	default:

cntr/fw/include/cntr/ep0.h

@@ -0,0 +1,62 @@
+/*
+ * include/cntr/ep0.h - EP0 extension protocol
+ *
+ * Written 2008-2010 by Werner Almesberger
+ * Copyright 2008-2010 Werner Almesberger
+ *
+ * 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.
+ */
+
+
+#ifndef EP0_H
+#define EP0_H
+
+/*
+ * Direction	bRequest		wValue		wIndex	wLength
+ *
+ * ->host	CNTR_ID		-		-	3
+ * ->host	CNTR_BUILD		-		-	#bytes
+ * host->	CNTR_RESET		-		-	0
+ *
+ * ->host	CNTR_READ		-		0	12
+ */
+
+/*
+ * EP0 protocol:
+ *
+ * 0.0	initial release
+ */
+
+#define EP0CNTR_MAJOR	0	/* EP0 protocol, major revision */
+#define EP0CNTR_MINOR	0	/* EP0 protocol, minor revision */
+
+
+/*
+ * bmRequestType:
+ *
+ * D7 D6..5 D4...0
+ * |  |     |
+ * direction (0 = host->dev)
+ *    type (2 = vendor)
+ *          recipient (0 = device)
+ */
+
+
+#define	CNTR_TO_DEV(req)	(0x40 | (req) << 8)
+#define	CNTR_FROM_DEV(req)	(0xc0 | (req) << 8)
+
+
+enum cntr_requests {
+	CNTR_ID			= 0x00,
+	CNTR_BUILD,
+	CNTR_RESET,
+	CNTR_READ		= 0x10,
+};
+
+
+void ep0_init(void);
+
+#endif /* !EP0_H */

cntr/tools/cntr/cntr.c

@@ -13,6 +13,7 @@
 
 #include <stdlib.h>
 #include <stdio.h>
+#include <signal.h>
 #include <usb.h>
 #include <sys/time.h>
 
@@ -28,6 +29,20 @@
 #define	BUF_SIZE		256
 
 
+static int debug = 0;
+static int verbose = 0;
+
+
+/* ----- CRC, shared with firmware ----------------------------------------- */
+
+
+/* crc32() */
+
+#include "cntr/crc32.c"
+
+
+/* ----- reset ------------------------------------------------------------- */
+
 
 static void reset_cntr(usb_dev_handle *dev)
 {
@@ -41,6 +56,9 @@ static void reset_cntr(usb_dev_handle *dev)
 }
 
 
+/* ----- identify ---------------------------------------------------------- */
+
+
 static void identify_cntr(usb_dev_handle *dev)
 {
 	const struct usb_device *device = usb_device(dev);
@@ -71,19 +89,32 @@ static void identify_cntr(usb_dev_handle *dev)
 }
 
 
+/* ----- measurements ------------------------------------------------------ */
+
+
 struct sample {
 	double t0, t1;
 	uint64_t cntr;
 };
 
 
-static void get_sample(usb_dev_handle *dev, struct sample *s)
+static unsigned packets = 0, crc_errors = 0, inv_errors = 0;
+static volatile int stop = 0;
+
+
+static void set_stop(int sig)
+{
+	stop = 1;
+}
+
+
+static int get_sample(usb_dev_handle *dev, struct sample *s)
 {
 	static uint32_t last = 0, high = 0;
 	struct timeval t0, t1;
-	int res;
-	uint8_t buf[4];
-	uint32_t cntr;
+	int res, bad;
+	uint8_t buf[12];
+	uint32_t cntr, inv, crc, expect;
 
 	gettimeofday(&t0, NULL);
 	res = usb_control_msg(dev, FROM_DEV, CNTR_READ, 0, 0,
@@ -93,27 +124,73 @@ static void get_sample(usb_dev_handle *dev, struct sample *s)
 		fprintf(stderr, "CNTR_READ: %s\n", usb_strerror());
 		exit(1);
 	}
+	packets++;
 	cntr = buf[0] | (buf[1] << 8) | (buf[2] << 16) | (buf[3] << 24);
+	crc = buf[4] | (buf[5] << 8) | (buf[6] << 16) | (buf[7] << 24);
+	inv = buf[8] | (buf[9] << 8) | (buf[10] << 16) | (buf[11] << 24);
+	expect = crc32(cntr, ~0);
+	bad = 0;
+	if (crc != expect) {
+		if (verbose)
+			fprintf(stderr, "\nCRC error (count 0x%08x->0x%08x "
+			    "CRC 0x%08x/0x%08x)\n",
+			    (unsigned) last, (unsigned) cntr, (unsigned) crc,
+			    (unsigned) expect);
+		bad = 1;
+		crc_errors++;
+	}
+	if (cntr != (inv ^ 0xffffffff)) {
+		if (verbose)
+			fprintf(stderr,
+			    "\ninverted counter error (0x%08x->0x%08x, "
+			    "inv 0x%08x)\n",
+			    (unsigned) last, (unsigned) cntr, (unsigned) inv);
+		bad = 1;
+		inv_errors++;
+	}
+	if (bad)
+		return 0;
 	if (last > cntr)
 		high++;
 	last = cntr;
 	s->t0 = t0.tv_sec+t0.tv_usec/1000000.0;
 	s->t1 = t1.tv_sec+t1.tv_usec/1000000.0;
 	s->cntr = (uint64_t) high << 32 | cntr;
+	if (debug)
+		printf("0x%llx 0x%lx\n", 
+		    (unsigned long long ) s->cntr, (unsigned long) cntr);
+	return 1;
 }
 
 
-static void measure(usb_dev_handle *dev, double clock_dev_s)
+static void measure(usb_dev_handle *dev, double clock_dev_s, double error_goal)
 {
 	struct sample start, now;
 	uint64_t dc;
 	double dt, f, error;
-	char *f_exp, error_exp;
+	char *f_exp, *error_exp;
+	int i;
 
-	get_sample(dev, &start);
-	while (1) {
+	signal(SIGINT, set_stop);
+
+	/*
+	 * The round-trip time for getting the first sample is one of the
+	 * error terms. The smaller we can make it, the better. Thus, we try a
+	 * few times to improve our first result.
+	 */
+	while (!get_sample(dev, &start));
+	for (i = 0; i != 10; i++) {
+		while (!get_sample(dev, &now));
+		if (now.t1-now.t0 < start.t1-start.t0) {
+			if (debug)
+				fprintf(stderr, "improve %g -> %g\n",
+				    start.t1-start.t0, now.t1-now.t0);
+			start = now;
+		}
+	}
+	while (!stop) {
 		usleep(100000);
-		get_sample(dev, &now);
+		while (!get_sample(dev, &now));
 		dc = now.cntr-start.cntr;
 		dt = now.t0-start.t0;
 		f = dc/dt;
@@ -133,40 +210,54 @@ static void measure(usb_dev_handle *dev, double clock_dev_s)
 		error += (start.t1-start.t0)/dt;/* start sample read */
 		error += (now.t1-now.t0)/dt;	/* last sample read */
 		error += clock_dev_s/dt;	/* system clock deviation */
-		if (error > 1) {
+		if (error >= 1) {
 			printf("\r(wait) ");
 			fflush(stdout);
 			continue;
 		}
+		if (dc && error <= error_goal)
+			stop = 1;
 
-		error_exp = 'k';
-		error *= 1000.0;	/* ppm */
+		error_exp = "%";
+		error *= 100.0;
+		if (error < 0.1) {
+			error_exp = " ppm";
+			error *= 10000.0;
 			if (error < 1.0) {
-			error_exp = 'm'; /* ppm */
+				error_exp = " ppb";
 				error *= 1000.0;
 			}
-		if (error < 1.0) {
-			error_exp = 'b'; /* ppb */
-			error *= 1000.0;
 		}
 		
-		printf("\r%6.1f %1.9f %sHz %3.3f pp%c ",
+		printf("\r%6.1f %1.9f %sHz %3.3f%s ",
 		    dt, f, f_exp, error, error_exp);
 		fflush(stdout);
 	}
+	printf(
+	    "\n%llu counts, %u packets, %u CRC error%s, %u invert error%s\n",
+	    (unsigned long long) (now.cntr-start.cntr),
+	    packets, crc_errors, crc_errors == 1 ? "" : "s",
+	    inv_errors, inv_errors == 1 ? "" : "s");
 }
 
 
+/* ----- command-line parsing ---------------------------------------------- */
+
+
 static void usage(const char *name)
 {
 	fprintf(stderr, 
-"usage: %s [clock_dev_s]\n"
+"usage: %s [-c clock_dev] [-d] [-v] [accuracy_ppm]\n"
 "%6s %s -i\n"
-"%6s %s r\n\n"
-"    clock_dev_s  is the maximum deviation of the system clock, in seconds\n"
+"%6s %s -r\n\n"
+"    accuracy_ppm stop when specified accuracy is reached (default: never\n"
+"                 stop)\n"
+"    -c clock_dev maximum deviation of the system clock, in seconds\n"
 "		  (default: %g s)\n"
+"    -d           debug mode. Print counter values.\n"
 "    -i           identify the CNTR board\n"
 "    -r           reset the CNTR board\n"
+"    -v           verbose reporting of communication errors\n"
     , name, "", name, "", name, DEFAULT_CLOCK_DEV_S);
 	exit(1);
 }
@@ -177,10 +268,19 @@ int main(int argc, char *const *argv)
 	usb_dev_handle *dev;
 	int c, identify = 0, reset = 0;
 	double clock_dev_s = DEFAULT_CLOCK_DEV_S;
+	double error_goal = 0;
 	char *end;
 
-	while ((c = getopt(argc, argv, "ir")) != EOF)
+	while ((c = getopt(argc, argv, "c:dir")) != EOF)
 		switch (c) {
+		case 'c':
+			clock_dev_s = strtod(argv[optind], &end);
+			if (*end)
+				usage(*argv);
+			break;
+		case 'd':
+			debug = 1;
+			break;
 		case 'i':
 			identify = 1;
 			break;
@@ -190,12 +290,14 @@ int main(int argc, char *const *argv)
 		default:
 			usage(*argv);
 		}
+	if (identify && reset)
+		usage(*argv);
 
 	switch (argc-optind) {
 	case 0:
 		break;
 	case 1:
-		clock_dev_s = strtod(argv[optind], &end);
+		error_goal = strtod(argv[optind], &end)/1000000.0;
 		if (*end)
 			usage(*argv);
 		break;
@@ -219,7 +321,7 @@ int main(int argc, char *const *argv)
 		return 0;
 	}
 
-	measure(dev, clock_dev_s);
+	measure(dev, clock_dev_s, error_goal);
 
 	return 0;
 }