Re: [PARPORT] EPP-Interface for line scan camera

David Campbell (
Tue, 17 Nov 1998 07:27:59 +0800

Date sent: Mon, 16 Nov 1998 23:03:09 +0100
From: "Jürgen Beckers" <>
Organization: EURECA GmbH
Subject: [PARPORT] EPP-Interface for line scan camera

> Hello,
> We are looking for an EPP driver to operate our cameras under a LINUX
> system. The driver must provide the readout of the camera without
> interrupts!!! (about 2000-5000 port accesses per readout)

Why without interrupts? Could you please clarify this?

There are two possible situations here:
a) timing is absolutely critical, millisecond delays will cause problems
b) make sure nothing is going to touch the parallel port during the transfer

For case "a" you would disable hardware IRQs for up to 0.005 seconds. Other
parts of the kernel will complain (PPP for example) but this will only be a
warning message which can be ignored safely (Alan Cox will flame me on that
statement, but the kernel wont crash).

For case "b" you can lock out other hardware from using the parallel port
(using parallel port sharing) but still allow hardware interrupts to occur.
This is a requirement for the ZIP driver since a magic sequence is used to
attach/deattach from the device. During long delays the ZIP driver allows other
tasks to run but keeps the parallel port for itself.

If you do use the parport (parallel port sharing) method make sure that the
driver will release the parallel port after 1 second. Should the parallel port
be locked out continuously for more than 2 seconds AND a ZIP drive is on the
same port the mid level SCSI driver panics, you have been warned.

Contact me off list should you require any more assistance with parallel ports
under linux.

David Campbell

Check for all Linux
parallel port solutions.

Current project list:
a) Maintain Linux ZIP drivers (need to update docs)
b) Get to the bottom of rumors of a third ZIP interface
c) Create Linux chipset specific parport drivers

Any assistance to clearing this list most welcome

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This archive was generated by hypermail 2.0b3 on Wed 30 Dec 1998 - 10:18:47 EST