[PARPORT] VT82C686B parallel port configuration advice needed

From: Michael Sokolov (msokolov@ivan.Harhan.ORG)
Date: Tue Aug 14 2001 - 20:26:37 EDT

  • Next message: Tim Waugh: "Re: [PARPORT] VT82C686B parallel port configuration advice needed"

    Hi there,

    I am porting Linux to a board built by the company I work for, and I'm looking
    for advice regarding the parallel port. Since our board has one and since we
    have to produce a Linux port that supports all devices that our product ships
    with, we have to support it.

    Our board (called Adirondack) is a dual PowerPC (hence Linux in question is
    Linux/PPC, current linuxppc_2_4_devel) and has a Via Tech VT82C686B south
    bridge, which is where the parallel port lives. I was pleased to see that Linux
    knows about this chip and supports its features (including determining the I/O
    port, IRQ, and DMA channel automatically rather than having the user set them).
    However, it expects it to be already configured by the BIOS, i.e., it will only
    use the I/O port, IRQ, and DMA channel assigned by the BIOS, and won't assign
    its own. If the parallel port is disabled when Linux boots, it stays disabled.

    Our board, however, has no PC BIOS or anything like it (instead the ROM
    firmware is like a VAX console), and when Linux boots, the parallel port is
    disabled. Basically, our philosophy is that the firmware brings up the board
    with the functionality of a VAX (which of course excludes PC parallel ports),
    and if the user's software (which is what Linux is) wants other functionality,
    such as that of a PC (which would include the parallel port), it is welcome to
    reprogram the chips accordingly.

    So, to support the parallel port in Linux on the Adirondack, I need to have
    Linux enable it. Don't panic, I'm not going to ask you to pollute the generic
    parallel port driver with PPC SBS Adirondack-specific stuff, I'll do it in my
    Linux booter. However, since there are many ways to configure the parallel port
    (ECP, EPP, etc) and the sole beneficiary of this configuration will be the
    Linux parallel port driver, it makes the most sense to ask you guys how you
    would like it to be configured.

    Among the VT82C686B Super-I/O configuration registers, there are two that deal
    with the parallel port. First are the bottom two bits in register E2, which

    00 Unidirectional mode
    01 ECP
    10 EPP
    11 Parallel Port Disable (default)

    The other register is F0, Parallel Port Control. Its bits are:

    7 PS2 Type BiDirectional Parallel Port
      0 Disable (default)
      1 Enable
    6 EPP Direction by Register not by IOW
      0 Disable (default)
      1 Enable
    5 EPP+ECP
      0 Disable (default)
      1 Enable
    4 EPP Version
      0 Version 1.9 (default)
      1 Version 1.7
    3:0 Reserved

    I can set these registers to anything, but I would like to know which
    configuration the Linux parallel port driver would like the best. TIA.

    Michael Sokolov				5791 VAN ALLEN WAY
    Software Engineer			CARLSBAD CA 92008-7321 USA
    SBS Technologies, Inc.			Phone: +1-760-438-6900 x2347
    Communications Products			    or +1-888-SBS-COMM x2347
    					Fax:   +1-760-438-6904
    					E-mail: msokolov@sbs.com
    					     or msokolov@ivan.Harhan.ORG

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