UM0851 datasheet(215/245 Pages) STMICROELECTRONICS

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UM0851

Miscellaneous device drivers

Doc ID 16604 Rev 2

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The default timeout period can be programmed by passing an argument to the watchdog

daemon in following manner.

# watchdog -T 60

9.2.5

Configuration options

The following kernel configuration options affect the watchdog. These configurations can be

selected through the "make menuconfig" interface in Linux.

9.2.6

References

●

linux-2.6.27/Documentation/watchdog.txt

9.3

Pulse width modulator (PWM) driver

In some embedded application areas there is the specific need for providing intermediate

amounts of power between off and on, for example to control the speed of a DC motor, to

vary the brightness of light in a lamp or just to reduce the power consumption in any type of

device connected to the system. Pulse Width Modulation is a very efficient technique that is

often used for this kind of purpose, since it does not waste power for heating resistors, like

when using a rheostat. Instead, PWM is a technique based on the modulation of the power

duty cycle.

SPEAr320 contains one PWM hardware block.

9.3.1

Hardware overview

Pulse width modulation (PWM) is a powerful technique for controlling analog circuits with a

microprocessor's digital outputs. PWM is a way of digitally encoding analog signal levels.

Through the use of high-resolution counters, the duty cycle of a square wave is modulated

to encode a specific analog signal level. The PWM signal is still digital because, at any given

instant of time, the full DC supply is either fully on or fully off. The voltage or current source

is supplied to the analog load by means of a repeating series of on and off pulses. The on-

time is the time during which the DC supply is applied to the load, and the off-time is the

period during which supply is switched off. Given a sufficient bandwidth, any analog value

can be encoded with PWM.

The term duty cycle describes the proportion of on time to the regular interval or period of

time; a low duty cycle corresponds to low power, because the power is off for most of the

time. Duty cycle is expressed in percent, 100% being fully on.

Table 57.

Linux kernel configurations

Configuration option

Comment

CONFIG_WATCHDOG

This enables the watchdog support in the Linux kernel

CONFIG_WATCHDOG_NOWAYOUT

Enabling this option means that even on closing watchdog

the timer would remain active and would eventually reset

the system if not refreshed. Hence the wdt cannot be

stopped once started.

CONFIG_SPEAR_SP805_WATCHDOG This enables SPEAr watchdog support

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