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    SubjectRe: Bogus serial port ttyS02
    On Wed, 13 Aug 2003, Richard B. Johnson wrote:
    > On Wed, 13 Aug 2003, Geert Uytterhoeven wrote:
    > > Linux always finds 3 serial ports instead of 2:
    > >
    > > | ttyS00 at 0x03f8 (irq = 4) is a 16550A
    > > | ttyS01 at 0x02f8 (irq = 3) is a 16550A
    > > | ttyS02 at 0x03e8 (irq = 4) is a 16450
    > >
    > > The last one is bogus.
    > First, this looks like ix86 stuff, not m68k. Drivers for ix86

    It's PPC, not m68k. Both PReP and CHRP have PC-style serial ports.

    > machines probe the de facto addresses for up to a maximum of
    > 4 8250-type UARTS. Those addresses are:
    > (0) 0x3f8
    > (1) 0x2f8
    > (2) 0x3e8
    > (3) 0x328
    > (from the Phoenix SYSTEM BIOS book)
    > Usually, there are several bits that are permanently 0 in
    > some of the registers. This is used to "positively" identify
    > the chip. Note that many IR devices are also connected
    > to 8250-type UARTS.
    > I would guess that you have two serial ports, plus another
    > UART that's used for IR (maybe a IR keyboard???).

    No, the Super I/O has only two serial ports, of which one can be used for IRDA.

    > You can do `od /dev/ttyS2` from the root account and see
    > what happends.

    Nothing, it just waits for data. The same for `echo hello > /dev/ttyS2'. So the
    serial driver things it has to wait to accept/send data.



    Geert Uytterhoeven -- There's lots of Linux beyond ia32 --

    In personal conversations with technical people, I call myself a hacker. But
    when I'm talking to journalists I just say "programmer" or something like that.
    -- Linus Torvalds

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