Writing Device Drivers


The VMEbus supports multiple address spaces. Appropriate entries in the driver.conf(4) file should be made for the address spaces used by the device For DMA devices, the address space that the board uses for its DMA transfers must be known by the driver (this is usually a 32- or 24-bit space).

A VMEbus card has its own address, possibly configurable by jumpers. A VMEbus card has the same address no matter which slot it is plugged into. Changing the address of a VME card causes the system to treat it as a new device.

The VMEbus uses vectored interrupts. When a VMEbus device interrupts, the system can identify which device is interrupting and call the correct device driver directly.

VMEbus Hardware Configuration Files

Most VME devices require hardware configuration files to inform the system that the device hardware may be present. The configuration file must specify the device addresses on the VMEbus and any interrupt capabilities that the device has.

Configuration files for VMEbus devices should identify the parent bus driver implicitly using the class keyword and specifying class "vme." This removes the dependency on the name of the particular bus driver involved, since the driver may be named differently on different platforms. See driver.conf(4) and vme(4) for further details.