Linux Device Drivers, Second Edition

Quick Reference

This chapter introduced the following symbols:

#include <linux/param.h> , HZ

The HZ symbol specifies the number of clock ticks generated per second.

#include <linux/sched.h> , volatile unsigned long jiffies

The jiffies variable is incremented once for each clock tick; thus, it’s incremented HZ times per second.

#include <asm/msr.h> , rdtsc(low,high); , rdtscl(low);

Read the timestamp counter or its lower half. The header and macros are specific to PC-class processors; other platforms may need asm constructs to achieve similar results.

extern struct timeval xtime;

The current time, as calculated at the last timer tick.

#include <linux/time.h> , void do_gettimeofday(struct timeval *tv); , void get_fast_time(struct timeval *tv);

The functions return the current time; the former is very high resolution, the latter may be faster while giving coarser resolution.

#include <linux/delay.h> , void udelay(unsigned long usecs); , void mdelay(unsigned long msecs);

The functions introduce delays of an integer number of microseconds and milliseconds. The former should be used to wait for no longer than one millisecond; the latter should be used with extreme care because these delays are both busy-loops.

int in_interrupt();

Returns nonzero if the processor is currently running in interrupt mode.

#include <linux/tqueue.h> , DECLARE_TASK_QUEUE(variablename);

The macro declares a new variable and initializes it.

void queue_task(struct ...