Messages in this thread |  | | | Date | Mon, 27 Aug 2001 12:22:29 -0700 | | From | "Randy.Dunlap" <> | | Subject | Re: time question |
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Bart Vandewoestyne wrote: > > I'm trying to port the DOS driver for a data aquisition card to linux > (http::/mc303.ulyssis.org). It is my first linux driver writing > attempt. Somewhere in the code i have the following lines of DOS-code > that do some busy waiting: > > _bios_timeofday(_TIME_GETCLOCK,&tb); l = tb; > while(l-tb < 2) _bios_timeofday(_TIME_GETCLOCK,&l); > > What is the best linux equivalent for this?
I don't have a DOS system + development tools handy. Can you tell me what _bios_timeofday(_TIME_GETCLOCK, ptr) compiles/ assembles to? I.e., what software interrupt, and what the AH register is set to on entry?
I'm guessing that this code is just doing a 2-tick delay (18.2 ticks per second), using int. 0x1a, AH=00 (http://www.ctyme.com/intr/rb-2271.htm). This means that each tick is approximately 55 ms, so the code is delaying for about 110 ms.
Take a look at the new Linux Device Drivers book (second edition), in the "Flow of Time" chapeter: http://www.xml.com/ldd/chapter/book/ch06.html You may get some answers there.
To begin with, you could try using mdelay(110);
Is this busy-waiting loop used seldom or often? If seldom, then using mdelay() might be OK. If often, then a sleep queue seems to be preferred. Read the LDD Time chapter.
You might also try kernelnewbies.org for introductory kernel questions. See the FAQ and the /documents/ directory.
>From your list of questions:
1. What kind of device do I need? Right now I am trying a character device, but is this indeed what we need???
A: Yes. If it's not a block device and not a network device, it's usually a character device.
2. If I need a character device, what linux-existing driver is good to look at and learn from it?
A: I'm not aware of other data acq drivers in the kernel, but that's just not my area. Are there any (anyone)?
3. How should I translate the assembler code of the DOS driver? Can I use linux native system calls? To what linux sytem calls can I map the inplI and outplI functions?
A: Sure, you can use native Linux system calls, if you know which ones to use. However, some calls may actually be (g)lib calls instead of system calls.
inplI(): same as inpl() on your web page (since bswap is commented). Maps to: value = inl(port);
outplI(): Only difference here is the 16-bit word-order of the 32-bit value to write to the I/O port. I'd suggest just getting the data order correct in the calling function and using outl(value, port); in Linux drivers.
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