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RE: parport ECP & DMA
Thanks for your reply.
> In our non-Linux based products (e.g. the
> printservers) we use ECP a lot so we know that the ECP
> mode in the ETRAX 100LX works well.
Good to hear that ;-)
> The switching between forward and reverse mode has to be
> made manually.
> There are two ways to solve this:
> 1. Some protocols used over parallel ports are based on
> commands and responses. In this case the port can be
> switched to forward just before the command and then
> to reverse just after the command.
> 2. For applications where the bulk of the data is
> in one direction you can poll the other direction
> by reverseing the port once in a while. This works
> well with e.g. printers.
> Can you describe the protocol that will run on your
> parallel port?
It's a proprietary protocol, the peripheral does some
data acquisition for us, changes on it's inputs will be
reported to us.
Also, data can be sent out to the peripheral, which will
be used by the peripheral for tasks completely unrelated
to the data acquisition.
The flow of data is completely unpredictable, so it could
mean we have to switch from forward to reverse and vica versa
I first thought of keeping the port in reverse mode all the
time, allowing the peripheral to send its data whenever
needed, and temporarily switching to forward whenever
we have to send something out.
But when we have to send a lot of data during a longer
period of time, this would still mean we would have to
switch between forward / reverse mode way to often.
We're currently considering to use the two parallel ports,
one as dedicated input, the other as dedicated output.
I guess it won't be a problem, keeping a port in
ecp_rev / ecp_forw and dma enabled all the time?