Motorola MCP750 Specifications download pdf (Page 299)

Writing a User-Level Device Drive

17-23

The vme_address(3C) Library Routine 17

The vme_address(3C) routine enables you to obtain a 32-bit physical address for an

A16 or an A24 (H)VME address generated by a particular device. A 32-bit physical

address is required when you use the shmbind(2) system call or the shmconfig(1M)

command to bind a shared memory region to a section of physical (H)VME memory. You

might find this routine particularly helpful when you are writing a user-level device driver

and need to bind a shared memory region to the physical address of the (H)VME board.

Use of vme_address(3C) is explained in the PowerUX Real-Time Guide; reference

information is provided in the corresponding system manual page.

Developing the Driver’s I/O Service Routines 17

A standard interface has been defined for a user-level device driver’s open, close,

aread, awrite, acheck, await, and control routines. The standard interface for each

of these routines is described in the sections that follow. User-level device drivers written

by Concurrent Computer Corporation personnel must adhere to the standard interfaces.

The following information is provided for each type of routine.

• A description of the routine and implementation guidelines

• The C speciﬁcation

• Detailed descriptions of each parameter

• The return value

The open routine is described in “The open Routine” on page 17-23. The asynchronous

I/O support routines are described in “The Asynchronous I/O Support Routines” on page

17-25. The control functions are described in “Control Functions” on page 17-30. The

close routine is described in “The close Routine” on page 17-31.

The open Routine 17

The driver’s open routine allows a user process to open a device in preparation for I/O or

control operations. It is responsible for performing any initialization that is necessary to

use the device. It attaches the driver status region and the device register region to the

calling process’s virtual address space. To perform these functions, the open routine

must make the following calls for each region:

ftok(3C) to obtain an IPC key that is based on the path name of the device

and a character that uniquely identifies a group of cooperating

processes. Note that ftok returns the same key for linked files

when it is called with the same path name and identiﬁer; it returns

different keys when called with the same path name and different

identiﬁers.

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Motorola MCP750 Specifications Page 299