[PARPORT] Re: fifo recovery in EPF mode

From: Tim Waugh (twaugh@redhat.com)
Date: Thu Dec 20 2001 - 10:58:00 EST

  • Next message: Tom Perkins: "[PARPORT] Re: fifo recovery in EPF mode"

    On Thu, Dec 20, 2001 at 10:19:04AM -0500, Tom Perkins wrote:

    > Been busy testing the patches (in mass) that we've previously discussed.


    > The "patch" is getting pretty large. The coding is complete I think but
    > debugging isn't. Would you like to review the "patch" before I finished
    > my testing? And what if anything to you want with it? There are code
    > paths I don't have the hardware to test (nothing in true ECP for ex.).

    How large? If you like, send it to me in private mail and I'll put it
    on people.redhat.com for people to look and and play with.

    > And finally, I think the fifo stuck code in function
    > "parport_pc_compat_write_block_pio" should drop any attempt at recovery.

    Well, we should do something to make it reliable. Whether that should
    just be to reset the FIFO and take off the FIFO depth from the byte
    count I don't know.

    > My reasoning is as follows: In compatible mode your not performing a
    > true block operation like in ECP your just sending a window on a stream.

    It's the same thing. It's just a byte stream in both cases. (Okay,
    ECP has an address-or-data tag for each byte, but still.)

    > When the "fifo sticks" in this mode there doesn't appear to be a
    > reliable (across all chipsets) way of stopping the transfer and putting
    > the chip in ECR_TST.

    I think we agreed that ECR_TST was the wrong way to go. You have to
    go through mode 000 or 001 before doing anything, and that means
    resetting the FIFO. We don't do that now; I think you said your patch
    would fix that.

    > However, since we've working in compatible mode the
    > fifo should be already full at time-out occurrence.

    It won't necessarily be full. The printer might be taken off-line
    half-way through the last full FIFO run. But it's a small window I

    > Now if on time-out we immediately switch to ECR_PS2 mode (while we
    > have the fifo full condition) we already know the recovery point and
    > this would minimize the window for data corruption to microseconds
    > at best.

    Yes. At least we know that will work, and most of the cases will be


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