Date: Sun, 22 Jan 2012 13:57:03 +0100 From: Patrick Lamaiziere <patfbsd@davenulle.org> To: Gerhard Strangar <g.s@arcor.de> Cc: freebsd-drivers@freebsd.org Subject: Re: Introduction to writing kernel modules Message-ID: <20120122135703.15810f3f@davenulle.org> In-Reply-To: <4F1BEE87.6080303@arcor.de> References: <4F1BEE87.6080303@arcor.de>
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Le Sun, 22 Jan 2012 12:09:59 +0100,
Gerhard Strangar <g.s@arcor.de> a écrit :
> Hello,
Hello,
> I'm trying to write a driver for my watchdog card. However I don't
> know anything about kernel modules in FreeBSD. I'm running 8.2
> Release and I found /usr/src/share/examples/drivers/, but there are
> lines like
>
> struct ${1}_softc {
> [...]
> char buffer[BUFFERSIZE]; /* If we need to buffer something. */
> };
>
> Does it mean that it's for internal use of the example module only or
> does an other component use it?
The softc is used to store private informations (but I guess you can
store public information too). Each instance of the driver owns its
softc. I mean that if you have two network cards like "em0, em1" there
will be two softc allocated, one for each.
> My card is PCI-based and all I need to do is write a byte via
> port-based IO, no Interrupts, no DMA or other stuff. I'm planning to
> use a character device for triggering the timer reset or disabling
> the card. But I don't need to copy the input to kernel space before
> checking if it was 0 or 1, do I?
There is a facility for watchdogs, you should use it. You only have to
register you watchdog in the kernel and watchdogd(8) is used to
control the watchdog from userland.
introduction:
http://web.archive.org/web/20040629062401/http://ezine.daemonnews.org/200406/watchdog.html
also see man 9 watchdog.
> Later on, the example uses:
> static struct _pcsid
> {
> u_int32_t type;
> const char *desc;
> } pci_ids[] = {
> { 0x1234abcd, "ACME PCI Widgetplus" },
> { 0x1243fedc, "Happy moon brand RIPOFFplus" },
> { 0x00000000, NULL }
> };
>
> What's the meaning of those? Is the driver looking for two cards and
> 0x0 and NULL terminate the list or is it looking for one card only
> and the abcd matches the "class" of "pcilist -lv" and fedc matches
> "card"?
It is looking for two cards.
Few docs / papers about the kernel are listed here :
http://forums.freebsd.org/showthread.php?t=1566
And you can use the kernel cross reference to dig into the code:
http://fxr.watson.org/. You will find few examples of kernel watchdogs.
Regards.
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