Re: Raspberry Pi 3B USB Printing Issue

On 3/12/22 16:31, Archimedes Gaviola wrote:
>>
>> IOERROR usually means an electrical error. The RPI3B will use a
>> transaction translator for the FULL speed traffic, which is driven by
>> software.
> 

Hi Archimedes,

> Hi Hans,
> 
> I'm curious about the transaction translator you've mentioned, any idea why
> there's a need for translation and what is being translated? 

When the High Speed USB HUB was invented, there was a need to support 
FULL and LOW speed USB transactions. Because FULL and LOW speed 
transactions are slow and take up much bandwidth, a transactions 
translator was invented which translates between High Speed USB and 
FULL/LOW speed USB. That means the RPi 3B consists of a single USB HIGH 
speed port, followed by a USB HUB. These transactions are not visible in 
usbdump .

 >Does this only
> happen when RPi 3B (acting as host controller) is transmitting data to the
> Epson printer? Are translation events visible in the usbdump? In this case
> there's a way to possibly track what's going on and how to identify any
> info that is being translated? 

By turning on the HC debugging, you can possibly track via debug 
messages what is going on. Maybe it is a timing issue, that the SW is 
too slow serving the micro transactions.

Any idea also if translation is being
> performed in RPi 4B? 

The later RPi's do the transaction translator bits in HW or via the XHCI 
block.

As I have conducted several printing cases with my
> Epson printer without any issues with either of the 4 ports.
> 
> Sorry for these questions as I am catching-up to the USB technology
> internal workings under the hood.

You are welcome!

--HPS