Citeren Alexey Loukianov <[email protected]>:
Well, that is true and false in the same time. The trouble is that
usb-to-serial
implementations that are used in UPSes are totally messed up when it comes to
the compliance with USB standards regarding to HID.
That is *very* true. There are only a few vendors that took the effort
to make their USB to serial converters in the UPS compliant with
usbserial (PowerCOM being one of them).
So it might be either true
or not that the real MAX_READ_WRITE for device equals to reported 8 bytes.
That's the reason why we stick to 8 bytes. Devices that support
reading 64 bytes at a time will also allow to read in 8 chunks of 8
bytes (but not the other way around).
Winpower software on linux does reads in a chunks larger than 8
bytes and it is proven to work.
On this particular UPS. But it is also proven *not* to work on devices
with the same VID:PID combination. I tried that before and got burned
(see the archives).
In case of libusb-0.1.12 reading data in 8-bytes chunks works normally with
Ippon UPSes (unsure about other brands - it should be tested before doing any
commits to SVN),
Not easily. We don't have access to all these devices. Most of the
reports about drivers being broken are from users from the field, from
whom we usually never hear again until something breaks. I'm not
willing to take the risk to break this driver, if there are good
alternatives around.
but when using libusb-0.1.8 that is the stock version for RHEL4
reading in 8-bytes chunks makes phoenix usb-to-serial device in Ippon UPSes
hang.
In that case, we don't support this device with libusb-0.1.8. I don't
think we should consider patches that might break other devices that
are supported now, to add support for a library that is almost six
years old. The fact that even libusb-0.1.12 is almost four years old
tells me that we should probably up our minimum libusb requirements to
that instead.
Best regards, Arjen
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