Linux Device Drivers

Quick Reference

This chapter introduced the following symbols related to hardware management:

#include <asm/io.h> , unsigned inb(unsigned port); , void outb(unsigned char byte, unsigned port); , unsigned inw(unsigned port); , void outw(unsigned short word, unsigned port); , unsigned inl(unsigned port); , void outl(unsigned doubleword, unsigned port);

These functions are used to read and write I/O ports. They can also be called by user-space programs, provided they have the right privileges to access ports. Not all the platforms support all the functions, which depend on underlying hardware design.

SLOW_DOWN_IO; , unsigned inb_p(unsigned port); , ...

The statement SLOW_DOWN_IO is sometimes needed to deal with slow ISA boards on the x86 platform. If a small delay is needed after an I/O operation, you can use the six pausing counterparts of the functions introduced above, whose names end in _p.

void insb(unsigned port, void *addr, unsigned long count); , void outsb(unsigned port, void *addr, unsigned long count); , void insw(unsigned port, void *addr, unsigned long count); , void outsw(unsigned port, void *addr, unsigned long count); , void insl(unsigned port, void *addr, unsigned long count); , void outsl(unsigned port, void *addr, unsigned long count);

The ``string functions'' are optimized to transfer data from an input port to a region of memory, or the other way round. Such transfers are performed by reading or writing the same port count times.

unsigned readb(address); ...