add not about bugs/limitations under MacOS X

git-svn-id: svn:https://anonscm.debian.org/svn/pcsclite/trunk/Drivers/ccid@321 0ce88b0d-b2fd-0310-8134-9614164e65ea

README

@@ -30,6 +30,52 @@ Unsupported CCID readers:
 - none known
 
 
+Supported operating systems:
+============================
+
+- GNU/Linux (libusb 0.1.7)
+- MacOS X/Darwin (libusb 0.1.8beta, CVS snapshot. See "Known problems")
+ to libusb)
+
+
+Known problems:
+===============
+
+MacOS X/Darwin
+ readers enumeration
+
+ You may have wrong reader identification if you two or more reader
+ at the exact same time.
+ pcscd and the CCID driver do not list connected readers in the same
+ order. The driver has no way to know which reader has been
+ detected as a new reader by pcscd. So if you plug two readers at
+ the same time (for example if you start pcscd with two readers
+ connected or if you plug a USB hub with two readers on the hub)
+ you may have this (with two readers foo and bar):
+ - pcscd scans the USB bus and finds a new CCID reader foo and calls
+ the driver
+ - the CCID driver scan the USB bus and finds a new reader bar
+ - pcscd continues scanning the USB bus and finds the second reader
+ bar and calls the driver
+ - the CCID driver scan the USB bus and finds an unused reader foo.
+ Now the reader foo will be called bar by pcscd and bar will be
+ called foo.
+ We don't have this under Linux or *BSD since the USB bus scanning
+ method is the same for pcscd and the CCID driver.
+ One solution would be to use IFDHCreateChannelByName() instead of
+ IFDHCreateChannel() and specify the USB device to use.
+ Another solution is to plug readers one after the other and not at
+ the same time.
+
+ hotplug
+
+ Due to libusb work in progress the driver may crash on a reader
+ insertion after a few insert/remove actions.
+ So if your reader is always connected you should not have
+ problems.
+ A new version of libusb should fix this bug
+
+
 Licence:
 ========