[PATCH 1/2] amidi: ignore not only Active Sensing but all System Real-Time messages

[PATCH 1/2] amidi: ignore not only Active Sensing but all System Real-Time messages

[Clemens Ladisch]

By default, amidi ignores Active Sensing messages because they are sent
by many devices in the background and would only interfere with the
actual messages that amidi is supposed to capture.  However, there are
also devices that send Clock messages with the same problem, so it is
a better idea to filter out all System Real-Time messages.

Reported-by: Martin Tarenskeen <m.tarenskeen@zonnet.nl>
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
---
 amidi/amidi.1 |   19 +++++++++++++------
 amidi/amidi.c |   11 ++++++-----
 2 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/amidi/amidi.1 b/amidi/amidi.1
index 1b4cfb1..46e9c50 100644
--- a/amidi/amidi.1
+++ b/amidi/amidi.1
@@ -1,4 +1,4 @@
-.TH AMIDI 1 "26 Jun 2006"
+.TH AMIDI 1 "26 Mar 2016"

 .SH NAME
 amidi \- read from and write to ALSA RawMIDI ports
@@ -80,7 +80,7 @@ to record a Standard MIDI (.mid) file, use
 .B arecordmidi(1).

 .B amidi
-will filter out any Active Sensing bytes (FEh), unless the
+will filter out System Real-Time messages (F8h...FFh), unless the
 .I \-a
 option has been given.

@@ -91,7 +91,7 @@ Sends the bytes specified as hexadecimal numbers to the MIDI port.
 .TP
 .I \-d, \-\-dump
 Prints data received from the MIDI port as hexadecimal bytes.
-Active Sensing bytes (FEh) will not be shown, unless the
+System Real-Time messages (F8h...FFh) will not be shown, unless the
 .I \-a
 option has been given.

@@ -107,9 +107,16 @@ If this option has not been given, you must press Ctrl+C (or kill
 to stop receiving data.

 .TP
-.I \-a, \-\-active\-sensing
-Does not ignore Active Sensing bytes (FEh) when saving or printing
-received MIDI commands.
+.I \-a, \-\-all\-messages
+Includes System Real-Time messages (F8h...FFh) when saving or
+printing received MIDI commands.
+By default, these messages are ignored.
+
+(Clock (F8h) or Active Sensing (FEh) messages are sent in the
+background by many devices, but typically are not wanted and would
+only clutter up
+.B amidi\fR's
+output.)

 .SH EXAMPLES

diff --git a/amidi/amidi.c b/amidi/amidi.c
index cedf18c..4978249 100644
--- a/amidi/amidi.c
+++ b/amidi/amidi.c
@@ -77,7 +77,7 @@ static void usage(void)
 		"-d, --dump             print received data as hexadecimal bytes\n"
 		"-t, --timeout=seconds  exits when no data has been received\n"
 		"                       for the specified duration\n"
-		"-a, --active-sensing   don't ignore active sensing bytes\n");
+		"-a, --all-messages     include system real-time messages\n");
 }

 static void version(void)
@@ -418,11 +418,12 @@ int main(int argc, char *argv[])
 		{"send-hex", 2, NULL, 'S'},
 		{"dump", 0, NULL, 'd'},
 		{"timeout", 1, NULL, 't'},
-		{"active-sensing", 0, NULL, 'a'},
+		{"all-messages", 0, NULL, 'a'},
+		{"active-sensing", 0, NULL, 'a'}, /* for backwards compatibility */
 		{ }
 	};
 	int c, err, ok = 0;
-	int ignore_active_sensing = 1;
+	int ignore_system_realtime = 1;
 	int do_send_hex = 0;

 	while ((c = getopt_long(argc, argv, short_options,
@@ -461,7 +462,7 @@ int main(int argc, char *argv[])
 			timeout = atoi(optarg);
 			break;
 		case 'a':
-			ignore_active_sensing = 0;
+			ignore_system_realtime = 0;
 			break;
 		default:
 			error("Try `amidi --help' for more information.");
@@ -589,7 +590,7 @@ int main(int argc, char *argv[])
 			}
 			length = 0;
 			for (i = 0; i < err; ++i)
-				if (!ignore_active_sensing || buf[i] != 0xfe)
+				if (!ignore_system_realtime || buf[i] < 0xf8)
 					buf[length++] = buf[i];
 			if (length == 0)
 				continue;

[PATCH 2/2] amidi: fix timeout handling

[Clemens Ladisch]

The timeout is not supposed to expire when ignored messages are
received.  This cannot be handled with the poll() timeout, so add
a separate timer.

Reported-by: Martin Tarenskeen <m.tarenskeen@zonnet.nl>
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
---
 amidi/amidi.c |   69 ++++++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 53 insertions(+), 16 deletions(-)

diff --git a/amidi/amidi.c b/amidi/amidi.c
index 4978249..a3515b1 100644
--- a/amidi/amidi.c
+++ b/amidi/amidi.c
@@ -25,9 +25,11 @@
 #include <stdarg.h>
 #include <string.h>
 #include <ctype.h>
+#include <math.h>
 #include <getopt.h>
 #include <errno.h>
 #include <signal.h>
+#include <sys/timerfd.h>
 #include <sys/types.h>
 #include <sys/poll.h>
 #include <sys/stat.h>
@@ -37,6 +39,8 @@
 #include "aconfig.h"
 #include "version.h"

+#define NSEC_PER_SEC 1000000000L
+
 static int do_device_list, do_rawmidi_list;
 static char *port_name = "default";
 static char *send_file_name;
@@ -46,7 +50,7 @@ static char *send_data;
 static int send_data_length;
 static int receive_file;
 static int dump;
-static int timeout;
+static float timeout;
 static int stop;
 static snd_rawmidi_t *input, **inputp;
 static snd_rawmidi_t *output, **outputp;
@@ -425,6 +429,7 @@ int main(int argc, char *argv[])
 	int c, err, ok = 0;
 	int ignore_system_realtime = 1;
 	int do_send_hex = 0;
+	struct itimerspec itimerspec = { .it_interval = { 0, 0 } };

 	while ((c = getopt_long(argc, argv, short_options,
 		     		long_options, NULL)) != -1) {
@@ -459,7 +464,7 @@ int main(int argc, char *argv[])
 			dump = 1;
 			break;
 		case 't':
-			timeout = atoi(optarg);
+			timeout = atof(optarg);
 			break;
 		case 'a':
 			ignore_system_realtime = 0;
@@ -547,40 +552,64 @@ int main(int argc, char *argv[])

 	if (inputp) {
 		int read = 0;
-		int npfds, time = 0;
+		int npfds;
 		struct pollfd *pfds;

-		timeout *= 1000;
-		npfds = snd_rawmidi_poll_descriptors_count(input);
+		npfds = 1 + snd_rawmidi_poll_descriptors_count(input);
 		pfds = alloca(npfds * sizeof(struct pollfd));
-		snd_rawmidi_poll_descriptors(input, pfds, npfds);
+
+		if (timeout > 0) {
+			pfds[0].fd = timerfd_create(CLOCK_MONOTONIC, 0);
+			if (pfds[0].fd == -1) {
+				error("cannot create timer: %s", strerror(errno));
+				goto _exit;
+			}
+			pfds[0].events = POLLIN;
+		} else {
+			pfds[0].fd = -1;
+		}
+
+		snd_rawmidi_poll_descriptors(input, &pfds[1], npfds - 1);
+
 		signal(SIGINT, sig_handler);
+
+		if (timeout > 0) {
+			float timeout_int;
+
+			itimerspec.it_value.tv_nsec = modff(timeout, &timeout_int) * NSEC_PER_SEC;
+			itimerspec.it_value.tv_sec = timeout_int;
+			err = timerfd_settime(pfds[0].fd, 0, &itimerspec, NULL);
+			if (err < 0) {
+				error("cannot set timer: %s", strerror(errno));
+				goto _exit;
+			}
+		}
 		for (;;) {
 			unsigned char buf[256];
 			int i, length;
 			unsigned short revents;

-			err = poll(pfds, npfds, 200);
+			err = poll(pfds, npfds, -1);
 			if (stop || (err < 0 && errno == EINTR))
 				break;
 			if (err < 0) {
 				error("poll failed: %s", strerror(errno));
 				break;
 			}
-			if (err == 0) {
-				time += 200;
-				if (timeout && time >= timeout)
-					break;
-				continue;
-			}
-			if ((err = snd_rawmidi_poll_descriptors_revents(input, pfds, npfds, &revents)) < 0) {
+
+			err = snd_rawmidi_poll_descriptors_revents(input, &pfds[1], npfds - 1, &revents);
+			if (err < 0) {
 				error("cannot get poll events: %s", snd_strerror(errno));
 				break;
 			}
 			if (revents & (POLLERR | POLLHUP))
 				break;
-			if (!(revents & POLLIN))
+			if (!(revents & POLLIN)) {
+				if (pfds[0].revents & POLLIN)
+					break;
 				continue;
+			}
+
 			err = snd_rawmidi_read(input, buf, sizeof(buf));
 			if (err == -EAGAIN)
 				continue;
@@ -595,7 +624,7 @@ int main(int argc, char *argv[])
 			if (length == 0)
 				continue;
 			read += length;
-			time = 0;
+
 			if (receive_file != -1)
 				write(receive_file, buf, length);
 			if (dump) {
@@ -603,6 +632,14 @@ int main(int argc, char *argv[])
 					print_byte(buf[i]);
 				fflush(stdout);
 			}
+
+			if (timeout > 0) {
+				err = timerfd_settime(pfds[0].fd, 0, &itimerspec, NULL);
+				if (err < 0) {
+					error("cannot set timer: %s", strerror(errno));
+					break;
+				}
+			}
 		}
 		if (isatty(fileno(stdout)))
 			printf("\n%d bytes read\n", read);

Re: [PATCH 1/2] amidi: ignore not only Active Sensing but all System Real-Time messages

[Ricard Wanderlof]

On Sun, 10 Apr 2016, Clemens Ladisch wrote:

> By default, amidi ignores Active Sensing messages because they are sent
> by many devices in the background and would only interfere with the
> actual messages that amidi is supposed to capture.  However, there are
> also devices that send Clock messages with the same problem, so it is
> a better idea to filter out all System Real-Time messages.

I would argue that it would be better to have both options, somehow. I.e. 
active sensing is mostly a nuisance, but I can imagine occasions 
(analyzing the output from a sequencer perhaps) where one would want to 
keep the rest of the real time messages.

/Ricard
-- 
Ricard Wolf Wanderlöf                           ricardw(at)axis.com
Axis Communications AB, Lund, Sweden            www.axis.com
Phone +46 46 272 2016                           Fax +46 46 13 61 30

Re: [PATCH 1/2] amidi: ignore not only Active Sensing but all System Real-Time messages

[Martin Tarenskeen]

On Mon, 11 Apr 2016, Ricard Wanderlof wrote:

>
> On Sun, 10 Apr 2016, Clemens Ladisch wrote:
>
>> By default, amidi ignores Active Sensing messages because they are sent
>> by many devices in the background and would only interfere with the
>> actual messages that amidi is supposed to capture.  However, there are
>> also devices that send Clock messages with the same problem, so it is
>> a better idea to filter out all System Real-Time messages.
>
> I would argue that it would be better to have both options, somehow. I.e.
> active sensing is mostly a nuisance, but I can imagine occasions
> (analyzing the output from a sequencer perhaps) where one would want to
> keep the rest of the real time messages.

Hi,

I can see your point. I have been thinking about that but my coding skills 
are somewhat limited. I can image keeping the -a (--allow-realtime) option 
the way it is and adding a new option -c (--allow-clock) to allow 
receiving of 0xf8 midiclock messages. At the same time 0xf8 should be 
filtered by default, just like 0xfe. The other realtime messages are much 
less a problem because they are not sent continuously (e.g. start and 
stop)

What do you think Clemens Ladich, is this doable?

-- 

Martin Tarenskeen

Re: [PATCH 1/2] amidi: ignore not only Active Sensing but all System Real-Time messages

[Martin Tarenskeen]

On Mon, 11 Apr 2016, Martin Tarenskeen wrote:

> I can image keeping the -a (--allow-realtime) option 
> the way it is

I meant to write -a (--active-sensing

--allow-realtime is what I have now in my home-hacked patched version.

-- 

MT

Re: [PATCH 1/2] amidi: ignore not only Active Sensing but all System Real-Time messages

[Clemens Ladisch]

Ricard Wanderlof wrote:
> On Sun, 10 Apr 2016, Clemens Ladisch wrote:
>> By default, amidi ignores Active Sensing messages because they are sent
>> by many devices in the background and would only interfere with the
>> actual messages that amidi is supposed to capture.  However, there are
>> also devices that send Clock messages with the same problem, so it is
>> a better idea to filter out all System Real-Time messages.
>
> I would argue that it would be better to have both options, somehow. I.e.
> active sensing is mostly a nuisance, but I can imagine occasions
> (analyzing the output from a sequencer perhaps) where one would want to
> keep the rest of the real time messages.

I can imagine this too, and even more complex filters.

But the amidi tool is designed to be simple, and works on the lowest
level, with raw MIDI bytes.  This makes it appropriate to handle SysEx
stuff and to debug low-level hardware problems, but when you care about
the semantics of the messages, you should use a higher-level tool, such
as aseqdump.

Filtering out clock messages serves an actual need.  But I am not
willing to add complexity for a problem that is, at the moment, nothing
but a figment of our imaginations.


Regards,
Clemens

Re: [PATCH 1/2] amidi: ignore not only Active Sensing but all System Real-Time messages

[Ricard Wanderlof]

On Mon, 11 Apr 2016, Clemens Ladisch wrote:

> Ricard Wanderlof wrote:
> >
> > I would argue that it would be better to have both options, somehow. I.e.
> > active sensing is mostly a nuisance, but I can imagine occasions
> > (analyzing the output from a sequencer perhaps) where one would want to
> > keep the rest of the real time messages.
> 
> I can imagine this too, and even more complex filters.
> 
> But the amidi tool is designed to be simple, and works on the lowest
> level, with raw MIDI bytes.  This makes it appropriate to handle SysEx
> stuff and to debug low-level hardware problems, but when you care about
> the semantics of the messages, you should use a higher-level tool, such
> as aseqdump.
> 
> Filtering out clock messages serves an actual need.  But I am not
> willing to add complexity for a problem that is, at the moment, nothing
> but a figment of our imaginations.

My argument is really that currently amidi has an option for filtering out 
active sensing, which has probably been added as it serves a useful 
purpose in its own right. The patch replaces that filter with one that 
filters out everything from F8 (clock) and up, I think it would be better 
to keep the existing option, and add a new one, rather than to essentially 
change the meaning of the existing option.

I agree that more advanced filtering should be left to another 
application. 

/Ricard
-- 
Ricard Wolf Wanderlöf                           ricardw(at)axis.com
Axis Communications AB, Lund, Sweden            www.axis.com
Phone +46 46 272 2016                           Fax +46 46 13 61 30

Re: [PATCH 1/2] amidi: ignore not only Active Sensing but all System Real-Time messages

[Clemens Ladisch]

Ricard Wanderlof wrote:
> On Mon, 11 Apr 2016, Clemens Ladisch wrote:
>> Ricard Wanderlof wrote:
>>> I would argue that it would be better to have both options, somehow. I.e.
>>> active sensing is mostly a nuisance, but I can imagine occasions
>>> (analyzing the output from a sequencer perhaps) where one would want to
>>> keep the rest of the real time messages.
>>
>> I can imagine this too, and even more complex filters.
>>
>> But the amidi tool is designed to be simple, and works on the lowest
>> level, with raw MIDI bytes.  This makes it appropriate to handle SysEx
>> stuff and to debug low-level hardware problems, but when you care about
>> the semantics of the messages, you should use a higher-level tool, such
>> as aseqdump.
>>
>> Filtering out clock messages serves an actual need.  But I am not
>> willing to add complexity for a problem that is, at the moment, nothing
>> but a figment of our imaginations.
>
> My argument is really that currently amidi has an option for filtering out
> active sensing, which has probably been added as it serves a useful
> purpose in its own right. The patch replaces that filter with one that
> filters out everything from F8 (clock) and up

I consider this change a bug fix; I just forgot about clock messages
when I originally impemented the filter.

> I think it would be better to keep the existing option, and add a new
> one, rather than to essentially change the meaning of the existing
> option.

That would be a new feature.


Regards,
Clemens

Re: [PATCH 1/2] amidi: ignore not only Active Sensing but all System Real-Time messages

[Ricard Wanderlof]

On Mon, 11 Apr 2016, Clemens Ladisch wrote:

> >> Filtering out clock messages serves an actual need.  But I am not
> >> willing to add complexity for a problem that is, at the moment, nothing
> >> but a figment of our imaginations.
> >
> > My argument is really that currently amidi has an option for filtering out
> > active sensing, which has probably been added as it serves a useful
> > purpose in its own right. The patch replaces that filter with one that
> > filters out everything from F8 (clock) and up
> 
> I consider this change a bug fix; I just forgot about clock messages
> when I originally impemented the filter.

Fair enough, although regardless of the original intention, the current 
version is out there (although I honestly haven't checked how long the 
filtering option has been available, perhaps it's not that long), and it's 
not buggy in the sense that it does what the corresponding (long) option 
says it will do.

> > I think it would be better to keep the existing option, and add a new
> > one, rather than to essentially change the meaning of the existing
> > option.
> 
> That would be a new feature.

Yes.

/Ricard
-- 
Ricard Wolf Wanderlöf                           ricardw(at)axis.com
Axis Communications AB, Lund, Sweden            www.axis.com
Phone +46 46 272 2016                           Fax +46 46 13 61 30

[PATCH v2 1/2] amidi: ignore not only Active Sensing but also Clock bytes

[Clemens Ladisch]

By default, amidi ignores Active Sensing messages because they are sent
by many devices in the background and would only interfere with the
actual messages that amidi is supposed to capture.  However, there are
also devices that send Clock messages with the same problem, so it is
a better idea to filter them out, too.

Reported-by: Martin Tarenskeen <m.tarenskeen@gmail.com>
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
---
 amidi/amidi.1 |   19 ++++++++++++++-----
 amidi/amidi.c |   13 +++++++++++--
 2 files changed, 25 insertions(+), 7 deletions(-)

v2: separate option for clock messages

diff --git a/amidi/amidi.1 b/amidi/amidi.1
index 1b4cfb1..86beb27 100644
--- a/amidi/amidi.1
+++ b/amidi/amidi.1
@@ -1,4 +1,4 @@
-.TH AMIDI 1 "26 Jun 2006"
+.TH AMIDI 1 "16 Apr 2016"

 .SH NAME
 amidi \- read from and write to ALSA RawMIDI ports
@@ -80,9 +80,11 @@ to record a Standard MIDI (.mid) file, use
 .B arecordmidi(1).

 .B amidi
-will filter out any Active Sensing bytes (FEh), unless the
+will filter out any Active Sensing and Clock bytes (FEh, F8h), unless the
 .I \-a
-option has been given.
+or
+.I \-c
+options have been given.

 .TP
 .I \-S, \-\-send\-hex="..."
@@ -91,9 +93,11 @@ Sends the bytes specified as hexadecimal numbers to the MIDI port.
 .TP
 .I \-d, \-\-dump
 Prints data received from the MIDI port as hexadecimal bytes.
-Active Sensing bytes (FEh) will not be shown, unless the
+Active Sensing and Clock bytes (FEh, F8h) will not be shown, unless the
 .I \-a
-option has been given.
+or
+.I \-c
+options have been given.

 This option is useful for debugging.

@@ -111,6 +115,11 @@ to stop receiving data.
 Does not ignore Active Sensing bytes (FEh) when saving or printing
 received MIDI commands.

+.TP
+.I \-c, \-\-clock
+Does not ignore Clock bytes (F8h) when saving or printing received
+MIDI commands.
+
 .SH EXAMPLES

 .TP
diff --git a/amidi/amidi.c b/amidi/amidi.c
index cedf18c..58ac814 100644
--- a/amidi/amidi.c
+++ b/amidi/amidi.c
@@ -77,7 +77,8 @@ static void usage(void)
 		"-d, --dump             print received data as hexadecimal bytes\n"
 		"-t, --timeout=seconds  exits when no data has been received\n"
 		"                       for the specified duration\n"
-		"-a, --active-sensing   don't ignore active sensing bytes\n");
+		"-a, --active-sensing   include active sensing bytes\n"
+		"-c, --clock            include clock bytes\n");
 }

 static void version(void)
@@ -419,10 +420,12 @@ int main(int argc, char *argv[])
 		{"dump", 0, NULL, 'd'},
 		{"timeout", 1, NULL, 't'},
 		{"active-sensing", 0, NULL, 'a'},
+		{"clock", 0, NULL, 'c'},
 		{ }
 	};
 	int c, err, ok = 0;
 	int ignore_active_sensing = 1;
+	int ignore_clock = 1;
 	int do_send_hex = 0;

 	while ((c = getopt_long(argc, argv, short_options,
@@ -463,6 +466,9 @@ int main(int argc, char *argv[])
 		case 'a':
 			ignore_active_sensing = 0;
 			break;
+		case 'c':
+			ignore_clock = 0;
+			break;
 		default:
 			error("Try `amidi --help' for more information.");
 			return 1;
@@ -589,7 +595,10 @@ int main(int argc, char *argv[])
 			}
 			length = 0;
 			for (i = 0; i < err; ++i)
-				if (!ignore_active_sensing || buf[i] != 0xfe)
+				if ((buf[i] != MIDI_CMD_COMMON_CLOCK &&
+				     buf[i] != MIDI_CMD_COMMON_SENSING) ||
+				    (buf[i] == MIDI_CMD_COMMON_CLOCK   && !ignore_clock) ||
+				    (buf[i] == MIDI_CMD_COMMON_SENSING && !ignore_active_sensing))
 					buf[length++] = buf[i];
 			if (length == 0)
 				continue;

[PATCH v2 2/2] amidi: fix timeout handling

[Clemens Ladisch]

The timeout is not supposed to expire when ignored messages are
received.  This cannot be handled with the poll() timeout, so add
a separate timer.

Reported-by: Martin Tarenskeen <m.tarenskeen@gmail.com>
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
---
 amidi/amidi.c |   69 ++++++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 53 insertions(+), 16 deletions(-)

no changes from v1

diff --git a/amidi/amidi.c b/amidi/amidi.c
index 58ac814..290df48 100644
--- a/amidi/amidi.c
+++ b/amidi/amidi.c
@@ -25,9 +25,11 @@
 #include <stdarg.h>
 #include <string.h>
 #include <ctype.h>
+#include <math.h>
 #include <getopt.h>
 #include <errno.h>
 #include <signal.h>
+#include <sys/timerfd.h>
 #include <sys/types.h>
 #include <sys/poll.h>
 #include <sys/stat.h>
@@ -37,6 +39,8 @@
 #include "aconfig.h"
 #include "version.h"

+#define NSEC_PER_SEC 1000000000L
+
 static int do_device_list, do_rawmidi_list;
 static char *port_name = "default";
 static char *send_file_name;
@@ -46,7 +50,7 @@ static char *send_data;
 static int send_data_length;
 static int receive_file;
 static int dump;
-static int timeout;
+static float timeout;
 static int stop;
 static snd_rawmidi_t *input, **inputp;
 static snd_rawmidi_t *output, **outputp;
@@ -427,6 +431,7 @@ int main(int argc, char *argv[])
 	int ignore_active_sensing = 1;
 	int ignore_clock = 1;
 	int do_send_hex = 0;
+	struct itimerspec itimerspec = { .it_interval = { 0, 0 } };

 	while ((c = getopt_long(argc, argv, short_options,
 		     		long_options, NULL)) != -1) {
@@ -461,7 +466,7 @@ int main(int argc, char *argv[])
 			dump = 1;
 			break;
 		case 't':
-			timeout = atoi(optarg);
+			timeout = atof(optarg);
 			break;
 		case 'a':
 			ignore_active_sensing = 0;
@@ -552,40 +557,64 @@ int main(int argc, char *argv[])

 	if (inputp) {
 		int read = 0;
-		int npfds, time = 0;
+		int npfds;
 		struct pollfd *pfds;

-		timeout *= 1000;
-		npfds = snd_rawmidi_poll_descriptors_count(input);
+		npfds = 1 + snd_rawmidi_poll_descriptors_count(input);
 		pfds = alloca(npfds * sizeof(struct pollfd));
-		snd_rawmidi_poll_descriptors(input, pfds, npfds);
+
+		if (timeout > 0) {
+			pfds[0].fd = timerfd_create(CLOCK_MONOTONIC, 0);
+			if (pfds[0].fd == -1) {
+				error("cannot create timer: %s", strerror(errno));
+				goto _exit;
+			}
+			pfds[0].events = POLLIN;
+		} else {
+			pfds[0].fd = -1;
+		}
+
+		snd_rawmidi_poll_descriptors(input, &pfds[1], npfds - 1);
+
 		signal(SIGINT, sig_handler);
+
+		if (timeout > 0) {
+			float timeout_int;
+
+			itimerspec.it_value.tv_nsec = modff(timeout, &timeout_int) * NSEC_PER_SEC;
+			itimerspec.it_value.tv_sec = timeout_int;
+			err = timerfd_settime(pfds[0].fd, 0, &itimerspec, NULL);
+			if (err < 0) {
+				error("cannot set timer: %s", strerror(errno));
+				goto _exit;
+			}
+		}
 		for (;;) {
 			unsigned char buf[256];
 			int i, length;
 			unsigned short revents;

-			err = poll(pfds, npfds, 200);
+			err = poll(pfds, npfds, -1);
 			if (stop || (err < 0 && errno == EINTR))
 				break;
 			if (err < 0) {
 				error("poll failed: %s", strerror(errno));
 				break;
 			}
-			if (err == 0) {
-				time += 200;
-				if (timeout && time >= timeout)
-					break;
-				continue;
-			}
-			if ((err = snd_rawmidi_poll_descriptors_revents(input, pfds, npfds, &revents)) < 0) {
+
+			err = snd_rawmidi_poll_descriptors_revents(input, &pfds[1], npfds - 1, &revents);
+			if (err < 0) {
 				error("cannot get poll events: %s", snd_strerror(errno));
 				break;
 			}
 			if (revents & (POLLERR | POLLHUP))
 				break;
-			if (!(revents & POLLIN))
+			if (!(revents & POLLIN)) {
+				if (pfds[0].revents & POLLIN)
+					break;
 				continue;
+			}
+
 			err = snd_rawmidi_read(input, buf, sizeof(buf));
 			if (err == -EAGAIN)
 				continue;
@@ -603,7 +632,7 @@ int main(int argc, char *argv[])
 			if (length == 0)
 				continue;
 			read += length;
-			time = 0;
+
 			if (receive_file != -1)
 				write(receive_file, buf, length);
 			if (dump) {
@@ -611,6 +640,14 @@ int main(int argc, char *argv[])
 					print_byte(buf[i]);
 				fflush(stdout);
 			}
+
+			if (timeout > 0) {
+				err = timerfd_settime(pfds[0].fd, 0, &itimerspec, NULL);
+				if (err < 0) {
+					error("cannot set timer: %s", strerror(errno));
+					break;
+				}
+			}
 		}
 		if (isatty(fileno(stdout)))
 			printf("\n%d bytes read\n", read);