[Nut-upsdev] blazer_usb: compatibility with Ippon BackPro UPSes (Phoenix Power Co., Ltd usb-to-serial controller)

[Arjen de Korte]

Citeren Alexey Loukianov <mooroon2 op mail.ru>:

> 1. megatec_usb and blazer_usb both read up data in 8-byte chunks.  
> Winpower do it in one large chunk.

This depends on what the interrupt endpoint supports. Both megatec_usb  
and blazer_usb can be used for widely different UPS makes and models.  
Not all support reading more than 8 bytes at a time (in fact, most  
don't). See the output of 'lsusb -vvv' for your UPS and lookup the  
following:

       Endpoint Descriptor:
         bLength                 7
         bDescriptorType         5
         bEndpointAddress     0x81  EP 1 IN
         bmAttributes            3
           Transfer Type            Interrupt
           Synch Type               None
           Usage Type               Data
         wMaxPacketSize     0x0008  1x 8 bytes

The collection of data when reading from the interrupt endpoint is  
possibly dealt with through some libusb implementations, but it is  
safer to do this in the driver itself.

> 2. blazer_usb tries to flush read buffer of controller before  
> sending a command.

This is needed by some devices supported through this driver.

> In the end I've got working blazer_usb on CentOS4 with stock libusb  
> (0.1.8). Key
> point was to read up data in one 64 byte chunk. It is still unclear  
> why does the
> data got corrupted in megatec_usb when read up in 8-bytes chunks,  
> and why does
> the device hang when using original blazer_usb with buffer-flush and 8-byte
> chunks read.

Most likely, the interrupt endpoint stalls. Since the flushing so far  
didn't clear stall conditions, it may hang. Improved now, thanks for  
the hint.

> 1. blazer_usb driver from SVN HEAD works correctly with USB Ippon UPSes on
> CentOS4, but require libusb version update. Version 0.1.12 from  
> CentOS5 will do.

Good. Thanks for the report.

> 2. megatec_usb driver somehow fails to read up correct data from USB  
> device. The
> cause of data corruption is unclear for me as it seems that the steps
> megatec_usb driver takes to read up data are almost the same as  
> blazer_usb take.

There is an error in the way how the megatec_usb driver deals with  
replies shorter than the 8 bytes it asks for.

> 3. It is possible to make blazer_usb work with RHEL4 version of  
> libusb (0.1.8),
> but it require modifications to the way it work. The patch that works on my
> setup is attached to this message.

Thanks for the patch, but that will badly break other devices with the  
same VID:PID combination. Therefor, this is not an option.

Best regards, Arjen
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