[cups.development] Re: Backchannel usage

[Josh Mathis]

After doing some more testing, it appears that the USB backend is not 
fetching the data from the printer until my rastertoxxx filter has 
exited (in most cases).

Just as a recap - I modified my filter to just send a status request to 
the printer. The printer should return 1 byte in reponse, which I 
attempt to read, then exit the filter.

In the error log, I see:

[Job xx] **MY Debug** Wrote status request
[Job xx] **MY Debug** Read -1 backchannel bytes
PID # (my filter) has exited with no errors.
[Job xx] *****DEBUG: Received 1 bytes of back-channel data!

In my filter, I write the status request and try reading from the 
backchannel. Once my filter exits, the USB backend gets the response. Is 
this the intended behavior, or is there a way I can trigger the USB 
backend to read any backchannel data from the printer without exiting my 
filter? Do I need to create a separate filter that simply writes the 
status request then exits and have my rastertoxxx filter read the 
backchannel when it starts?

One other thought - [K]ubuntu changed to a pre-empt kernel with Dapper. 
Could this cause such problems? I wouldn't immediately think so since 
all the filters should run with equal priority.

Thanks again,

Josh

Josh Mathis wrote:
> Matt Anderson wrote:
>> Josh Mathis wrote:
>>> So this raises two questions - why does the parallel backend not get
>>> anything at all back, and why does the USB get the return data too late?
>>
>> This is more of an "is it plugged in?" thing, but have you verified that
>> the parallel port is setup for bi-directional communication?
>>
>> -matt
>>
> 
> Being in tech support, I have to ask those questions too. :)
> 
> But yes, it is set up this way. I have another application which just 
> does status requesting and reading with direct write/read on the port, 
> and that works just fine. Permissions are also ok - I gave the cupsys 
> group full rights on the parallel port.
> 
> /Josh