[Leaplist] need some jiffies

[John Simpson]

On 2007-10-09, at 1052, Richard F. Ostrow Jr. wrote:
>
> Hmm... the last time I'd heard of the word "jiffies" was back when  
> I was
> coding on the C64 when I was 12 years old. I believe the definition  
> back
> then was more linked to machine cycles than any measurement of  
> time... so
> a jiffy on one machine will be different than a jiffy on another
> machine(hence a "jiffy" is not equal to x microseconds).

that's exactly what it is under linux. the kernel programs the timer  
chip to send interrupts 100 times per second. (for old-school DOS  
hackers, this is the same timer chip that DOS programs for 18.2 times  
per second. it uses hardware interrupt line 0, which maps to the  
processor's INT 0x08.)

the linux kernel's handler for that interrupt increments a "jiffy"  
counter, and it also calls the scheduler to cycle control of the CPU  
from one process to the next. (i'm sure it does more than just that,  
but those are the two most important things it's responsible for.)

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| John M. Simpson    ---   KG4ZOW   ---    Programmer At Large |
| http://www.jms1.net/                         <jms1 at jms1.net> |
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