Accessing I/O ports
When you're porting code that accesses hardware, the x86 architecture has a set of instructions that manipulate a separate address space called the I/O address space. This address space is completely separate from the memory address space. On non-x86 platforms, such an address space doesn't exist—all devices are mapped into memory.
In order to keep code portable, we've defined a number of functions that isolate this behavior. By including the file <hw/inout.h>, you get the following functions:
- in8()
- Reads an 8-bit value.
- in16(), inbe16(), inle16()
- Reads a 16-bit value.
- in32(), inbe32(), inle32()
- Reads a 32-bit value.
- in8s()
- Reads a number of 8-bit values.
- in16s()
- Reads a number of 16-bit values.
- in32s()
- Reads a number of 32-bit values.
- out8()
- Writes a 8-bit value.
- out16(), outbe16(), outle16()
- Writes a 16-bit value.
- out32(), outbe32(), outle32()
- Writes a 32-bit value.
- out8s()
- Writes a number of 8-bit values.
- out16s()
- Writes a number of 16-bit values.
- out32s()
- Writes a number of 32-bit values.
On the x86 architecture, these functions perform the machine
instructions in, out, rep ins*,
and rep outs*. On non-x86
architectures, they dereference the supplied address (the
addr parameter) and perform memory accesses.
Note that the calling process must use mmap_device_io() to access the device's I/O registers.