Filter
Top Products
Extensible Firmware Interface Specification
18-6 12/01/02 Version 1.10
Description
The DEVICE_IO.Mem(), .Io(), and .Pci() functions enable a driver to access device
registers in the appropriate memory or I/O space.
The I/O operations are carried out exactly as requested. The caller is responsible for any alignment
and I/O width issues which the bus, device, platform, or type of I/O might require. For example on
IA-32 platforms, width requests of IO_UINT64 do not work.
For Mem() and Io(), the address field is the bus relative address as seen by the device on the bus.
For Mem() and Io() the caller must align the starting address to be on a proper width boundary.
For Pci(), the address field is encoded as shown in Table 18-1. The caller must align the register
number being accessed to be on a proper width boundary.
Table 18-1. PCI Address
Mnemonic
Byte
Offset
Byte
Length
Description
Register 0 1 The register number on the function.
Function 1 1 The function on the device.
Device 2 1 The device on the bus.
Bus 3 1 The bus.
Segment 4 1 The segment number.
Reserved 5 3 Must be zero.
Status Codes Returned
EFI_SUCCESS The data was read from or written to the device.
EFI_INVALID_PARAMETER
Width is invalid.
EFI_OUT_OF_RESOURCES The request could not be completed due to a lack of resources.