Mentioned libusb problems. Updated fork section.

ChangeLog

@@ -1,3 +1,7 @@
+2003-12-26  Henning Meier-Geinitz <henning@meier-geinitz.de>
+
+	* README.darwin: Mentioned libusb problems. Updated fork section.
+
 2003-12-25  Henning Meier-Geinitz <henning@meier-geinitz.de>
 
 	* doc/descriptions-external/niash.desc: Added information that

README.darwin

@@ -18,6 +18,9 @@ sm3600 backend, disable sm3600 in dll.conf if you don't need it.
 
 Backends that use the function "fork" may not work at least with USB scanners.
 That's a limitation of MacOS X (doesn't use file descriptors for USB access).
+Some backends have been modified to use threads on MAcOS X qand should
+work. Others don't use fork at all. Both types of backends should work with
+MacOS X. Changing the backends to use threads is an ongoing effort.
 
 SCSI-scanners and Firewire scanners:
 ------------------------------------
@@ -30,15 +33,23 @@ sane-find-scanner is not able to find SCSI scanners on MacOS X yet.
 
 USB-scanners:
 -------------
-Work with libusb. Very limited testing until now. Try 
-"sane-find-scanner -v -v" and report success or failure to the SANE mailing
-list. Backends that use fork to create separate reader processes seem to fail.
-At least the following scanners are known to work:  UMax Astra 1220U and 2000U,
-Epson Perfection 1640SU and 2450 Photo.
+Work with libusb. Very limited testing until now. Try "sane-find-scanner -v -v"
+and report success or failure to the SANE mailing list. At least the following
+scanners are known to work: UMAX Astra 1220U and 2000U, Epson Perfection 1640SU
+and 2450 Photo.
+
+There are some known problems with libusb:
+
+- Older libusb versions return a wrong number of bytes written. Most backends
+  will return an error and won't work. Update your version of libusb.
+
+- Sometimes libusb doesn't detect your scanner. Try setting the environment
+  variable SANE_DEBUG_SANEI_USB to 255 (e.g. "setenv SANE_DEBUG_SANEI_USB 255"
+  or "export SANE_DEBUG_SANEI_USB=255) before running scanimage -L.
 
 Parport-scanners:
 -----------------
 I don't have any information about these. Please contact me or the SANE mailing
 list if you succeeded in using one of these.
 
-2003-08-21 Henning Meier-Geinitz <henning@meier-geinitz.de>
+2003-12-26 Henning Meier-Geinitz <henning@meier-geinitz.de>