Check your monitor's documentation and the USB 2.0 spec for asynchronous
transfers. Differences in how the monitor responds for supposedly-identical
command sets are generally issues with the monitor or communication, not the
command sets.
If you look at the pyusb source code, it's pretty much a simple wrapper for
libusb. That is, there's no real difference (except convenience in language
choice) between programming a driver using pyusb and programming one using
libusb.
That being said, I'm not entirely sure that pyusb includes support for the
asynchronous commands... and it was a fairly recent addition to libusb as
well. There's an outside chance that there's a bug in the asynch code, but
it's more likely there's a difference between the way the monitor handles
asynchronous vs. synchronous input
Also try isolating the particular sections of the code where the difference
happens. The file you sent is long, has no comments, and has very few print
statements. If you're debugging, add in lots more prints, preferably showing
the hex code for the transfers sent to & from the monitor at each write / read
command. Then compare those hex codes to each other for the sync and async
versions - and compare both to the USB spec and the programmer's manual for the
monitor.
-Sarah
--- On
Mon, 7/6/09, Scott Sibley <sisib...@gmail.com> wrote:
From: Scott Sibley <sisib...@gmail.com>
Subject: [Pyusb-users] Hoping for suggestions - libusb-1.0 related
To: pyusb-users@lists.sourceforge.net
Date: Monday, July 6, 2009, 8:04 PM
This isn't entirely pyusb related, but it could possibly affect the future of
pyusb.
I've been working on an LCD controller, with the goal of being able to control
multiple, concurrent devices. I needed USB support for my newest LCD, so I
began work on that using pyusb-0.1. However, it became clear pretty quickly
that I needed an asynchronous solution, so I set out to work on this wielding
ctypes and a fresh copy of libusb-1.0. I've run into some snags, overcoming
most (Python's GIL was getting in the way for instance), but there's this one
issue
that just won't go away. See, the operations work fine synchronously following
the steps below in sequence.
We can view asynchronous I/O as a 5 step process:
Allocation: allocate a libusb_transfer (This is self.transfer)Filling: populate
the libusb_transfer instance with information
about the transfer you wish to perform (libusb_fill_bulk_transfer)Submission:
ask libusb to submit the transfer (libusb_submit_transfer)Completion handling:
examine transfer results in the
libusb_transfer structure (libusb_handle_events and
libusb_handle_events_timeout)Deallocation: clean up resources (Not shown
below)However, when performing these steps asynchronously only a portion of the
LCD is filled with pixels. I've been through libusb's debug messages and
usbmon's output, and between async and sync there are no differences, except
when I look at the LCD for the results. I'm starting to believe that this is
just not possible with Python+ctypes, which is why I said this could possibly
affect pyusb. I am of course hoping for an answer to this, and having some
experience in both Python and libusb I'm hoping maybe you would have one. I've
attached some code if you feel up to looking into this.
Also, I have a question opened at Stackoverflow here:
http://stackoverflow.com/questions/1060305/usb-sync-vs-async-vs-semi-async-partially-answered-now
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