This chapter introduced the following symbols related to hardware management:
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#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.
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SLOW_DOWN_IO;,unsigned inb_p(unsigned port);,... The statement
SLOW_DOWN_IOis 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
counttimes.-
unsigned readb(address);,unsigned readw(address);,unsigned readl(address);,void writeb(unsigned value, address);,void writew(unsigned value, address);,void writel(unsigned value, address);,memset_io(address, value, count);,memcpy_fromio(dest, source, nbytes);,memcpy_toio(dest, source, nbytes); All of these functions are used to access I/O memory regions, either low ISA memory or high PCI buffers (after calling vremap).