|
|
Intel IA32 systems offer a 64KB (16-bit) I/O address space. Programmed I/O devices provide access to their internal registers through this I/O address space. This scheme is sometimes also called I/O-mapped I/O.
From the driver's point of view, accessing device registers involves reading to and writing from locations (ports) in the I/O space. The operating system provides special functions such as inb( ) and outb( ) to transfer data to and from device registers. Low-end floppy disk and tape drivers use this method to move data and control information to and from the device.
Both DDI and ODDI define functions to implement PIO:
| DDI | ODDI | Description |
|---|---|---|
| inb(D3) | inb(D3oddi) | Read a byte from an 8-bit I/O port |
| inl(D3) | ind(D3oddi) | Read a 32-bit word from a 32-bit I/O port |
| inw(D3) | inw(D3oddi) | Read a 16-bit short word from a 16-bit I/O port |
| outb(D3) | outb(D3oddi) | Write a byte to an 8-bit I/O port |
| outl(D3) | outd(D3oddi) | Write a 32-bit word to a 32-bit I/O port |
| outw(D3) | outw(D3oddi) | Write a 16-bit short word to a 16-bit I/O port |
| repinsb(D3) | repinsb(D3oddi) | Read bytes from an 8-bit I/O port to a buffer |
| repinsd(D3) | repinsd(D3oddi) | Read 32-bit words from a 32-bit I/O port to a buffer |
| repinsw(D3) | repinsw(D3oddi) | Read 16-bit short words from a 16-bit I/O port to a buffer |
| repoutsb(D3) | repoutsb(D3oddi) | Write bytes to an 8-bit I/O port from a buffer |
| repoutsd(D3) | repoutsd(D3oddi) | Write 32-bit words to a 32-bit I/O port from a buffer |
| repoutsw(D3) | repoutsw(D3oddi) | Write 16-bit short words to a 16-bit I/O port from a buffer |