time question

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?

Thanks,
mc303

Ing. Bart Vandewoestyne			 [email protected]
Hugo Verrieststraat 48			       GSM: +32 (0)478 397 697
B-8550 Zwevegem			 http://users.pandora.be/vandewoestyne
----------------------------------------------------------------------
"Any fool can know, the point is to understand." - Albert Einstein

Sorry, the URL should be: http://mc303.ulyssis.org/heim/

Greetings,
Bart

Ing. Bart Vandewoestyne			 [email protected]
Hugo Verrieststraat 48			       GSM: +32 (0)478 397 697
B-8550 Zwevegem			 http://users.pandora.be/vandewoestyne
----------------------------------------------------------------------
"Any fool can know, the point is to understand." - Albert Einstein

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.

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.

~Randy