UM0851 datasheet(26/245 Pages) STMICROELECTRONICS

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Platform section

UM0851

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Doc ID 16604 Rev 2

3.1.1

Hardware overview

SPEAr provides several GPTs acting as APB slaves. Each GPT consists of 2 independent

channels, each one made of a programmable 16-bit counter and a dedicated 8-bit timer

clock prescaler. The programmable 8-bit prescaler performs a clock division from 1 to 256.

Different input frequencies can be defined using SPEAr configuration registers.

The main features of the GPT module are listed below:

●

Each timer module provides two independent channels with separate control, count,

clock prescaler and interrupt registers

●

Each channel has 16-bit counter with a programmable timer interval

●

Provides auto-reload or single-shot mode feature

The following table shows GPTs available on different SPEAr platforms:

The following figure describes the GPT hardware interface.

Figure 2.

GPT hardware interface

The TIMER_CLK can be selected between a fixed 48 MHz source and PLL1, which is also

the source for the rest of the system. The PLL1 output also goes through a synthesizer

which can be programmed to derive the actual required operating GPT clock.

3.1.2

Software overview

SPEAr LSP provides proprietary software routines to allocate, program and use the general

purpose timer. This set of routines abstract the GPT hardware block and provide easy

kernel APIs to manage and control these timers. This layer does not provide any interface to

the user space.

The following figure explains the GPT framework as used by the kernel time keeping and

tick management subsystem. The GPT routines can also be directly used by user

modules/applications.

Table 10.

GPTs available on SPEAr

SPEAr600

SPEAr3xx

1 GPT in each CPU subsystem

2 in application subsystem

1 in basic subsystem

1 GPT in CPU subsystem

2 in basic subsystem

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