Register Access Overview

The Register Access platform service is intended for use in writing +device drivers. Writing device drivers involves frequent access to +hardware registers for reading, writing and modifying them.

+ What is a register

A register is +a memory location on the ASSP hardware to store data that relates +to the operation of that hardware. For example, a register can be +a counter, or a bit field, or the next sequence number or the next +byte or word of data that has arrived over a bus.

The Symbian +platform provides access functions for registers that have the following +sizes:

8–bit
16–bit
32–bit
64–bit

What +functions are available

There are three types of function +provided for register access:

Read - get the value of a register
Write - write a value to a register
Modify - use bitmasks to clear or set specific +bits in a register

Each function takes a first argument of a TLinAddr which is an address. The device driver only needs to know the address, +and the size of the register. The implementation of the Register Access +must map the exposed physical hardware register to a linear address.

Each type of function (read, write, modify) has 8–bit, 16–bit, +32–bit and 64–bit versions.

The Modify functions +take two bitmasks as parameters, to specify which bits to clear to +zero (clear mask) and which bits to set to one (set mask). This means +that you could call Modify16(myaddress, 0xC000,0x000F) and the top two bits would be set to zero, the bottom four bits +would be set to one, and the ten bits in the middle would retain their +current value.

See Register Access Client +Interface Guide for more details on each function and how to +use them.