Hello,
Up to now pcscd is polling the card driver every 400ms
(PCSCLITE_STATUS_POLL_RATE) to detect a card movement. This will wake
up the CPU constantly and consume power.
Many CCID readers (but not all) can use an asynchronous message to
send a card movement event to the host. This is supported in the CCID
driver [1] version 1.3.3 with support of TAG_IFD_POLLING_THREAD.
You need to use a snapshot of pcsc-lite [2] to use this feature.
My problem is that the libusb function usb_interrupt_read() is not
efficient and will poll using a 1ms timeout.
So instead of a polling every 400ms by pcscd we have a polling every
1ms by libusb. The situation is worse regarding CPU usage :-(
The problem in libusb has been discovered thanks to powertop [3] and
be corrected in the subversion revision 657 [4] of
/trunk/libusb/linux.c [5]. I backported the patch (attached) for
libusb 0.1.12.
But I have no idea when a new stable version of libusb (with the
correction) will be available.
So what should I do?
I plan to disable TAG_IFD_POLLING_THREAD in the CCID driver by default
and allow a way to activate it using the driver Info.plist file.
Other ideas? proposals? comments?
libusb 0.1.x will not evolve much. libusb 1.0 [6] is on its way and is
in competition with OpenUSB [7]. libusb 1.0 or OpenUSB have no stable
release yet.
Regards,
[1] http://pcsclite.alioth.debian.org/ccid.html
[2] http://ludovic.rousseau.free.fr/softwares/pcsc-lite/
[3] http://www.lesswatts.org/projects/powertop/
[4]
http://libusb.svn.sourceforge.net/viewvc/libusb/trunk/libusb/linux.c?r1=597&r2=657
[5]
http://libusb.svn.sourceforge.net/viewvc/libusb/trunk/libusb/linux.c?view=log
|6] http://libusb.wiki.sourceforge.net/Libusb1.0
[7] http://openusb.sourceforge.net/
--
Dr. Ludovic Rousseau
--- libusb-0.1.12/linux.c 2008-01-07 14:10:12.000000000 +0100
+++ libusb-0.1.12.poll/linux.c 2008-02-14 15:25:04.000000000 +0100
@@ -14,6 +14,7 @@
#include <errno.h>
#include <sys/time.h>
#include <dirent.h>
+#include <poll.h>
#include "linux.h"
#include "usbi.h"
@@ -164,7 +165,7 @@
{
struct usb_urb urb;
int bytesdone = 0, requested;
- struct timeval tv, tv_ref, tv_now;
+ struct timeval tv_ref, tv_now;
struct usb_urb *context;
int ret, waiting;
@@ -191,8 +192,6 @@
}
do {
- fd_set writefds;
-
requested = size - bytesdone;
if (requested > MAX_READ_WRITE)
requested = MAX_READ_WRITE;
@@ -217,20 +216,21 @@
waiting = 1;
context = NULL;
while (!urb.usercontext && ((ret = ioctl(dev->fd, IOCTL_USB_REAPURBNDELAY,
&context)) == -1) && waiting) {
- tv.tv_sec = 0;
- tv.tv_usec = 1000; // 1 msec
- FD_ZERO(&writefds);
- FD_SET(dev->fd, &writefds);
- select(dev->fd + 1, NULL, &writefds, NULL, &tv); //sub second wait
+ struct pollfd pollfd;
+ int poll_timeout = -1;
+
+ pollfd.fd = dev->fd;
+ pollfd.events = POLLOUT;
+ pollfd.revents = 0;
if (timeout) {
- /* compare with actual time, as the select timeout is not that precise
*/
gettimeofday(&tv_now, NULL);
-
- if ((tv_now.tv_sec > tv_ref.tv_sec) ||
- ((tv_now.tv_sec == tv_ref.tv_sec) && (tv_now.tv_usec >=
tv_ref.tv_usec)))
- waiting = 0;
+ poll_timeout = (tv_ref.tv_sec-tv_now.tv_sec)*1000 +
+ (tv_ref.tv_usec-tv_now.tv_usec)/1000;
}
+
+ if ((ret = poll(&pollfd, 1, poll_timeout)) != 1)
+ waiting = 0;
}
if (context && context != &urb) {
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