embedded c advanced

8/3/2019 Embedded C Advanced

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1/10/2012 Microcontroller 8051 1

Advanced programming

techniques withEmbedded C


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InterruptsInterrupts

The C51 compiler provides a method of callingThe C51 compiler provides a method of calling

a C function when an interrupt occursa C function when an interrupt occurs

This support allows you to create interruptThis support allows you to create interrupt

service routines in Cservice routines in C

The compiler automatically generates theThe compiler automatically generates the

interrupt vector and entry and exit code forinterrupt vector and entry and exit code for

the interrupt routinethe interrupt routine


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The The interruptinterrupt function attribute, when function attribute, when

included in a declaration, specifies that theincluded in a declaration, specifies that the

associated function is an interrupt functionassociated function is an interrupt function

The interrupt number and the register bankThe interrupt number and the register bank

are specifiedare specified

Additionally, you can specify the register bankAdditionally, you can specify the register bankused for that interrupt with the used for that interrupt with the usingusing

function attributefunction attribute


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ExampleExample

unsigned int interruptcnt;unsigned int interruptcnt;

unsigned char second;unsigned char second;

void timer0 (void) interrupt 1 using 2 {void timer0 (void) interrupt 1 using 2 {

if (++interruptcnt == 4000) {if (++interruptcnt == 4000) {

/* count to 4000 *//* count to 4000 */

second++;second++; /* second counter *//* second counter */

interruptcnt = 0;interruptcnt = 0; /* clear int counter *//* clear int counter */

}}


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Intrinsic Library RoutinesIntrinsic Library Routines

The libraries included with the compiler includeThe libraries included with the compiler includea number of routines that are implemented asa number of routines that are implemented as

intrinsic functionsintrinsic functions

NonNon--intrinsic functions generate ACALL orintrinsic functions generate ACALL orLCALL instructions to perform the libraryLCALL instructions to perform the library

routineroutine

Intrinsic functions generate inIntrinsic functions generate in--line code (whichline code (whichis faster and more efficient) to perform theis faster and more efficient) to perform the

library routinelibrary routine


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Intrinsic Function Description

_crol_crol_ Rotate character leftRotate character left_cror_ _cror_ Rotate character rightRotate character right

_irol_ _irol_ Rotate integer leftRotate integer left

_iror__iror_ Rotate integer rightRotate integer right

_lrol_ _lrol_ Rotate long integer leftRotate long integer left

_lror_ _lror_ Rotate long integer rightRotate long integer right

_nop_ _nop_ No operation (8051 NOPNo operation (8051 NOP

instruction)instruction)_testbit__testbit_ Test and clear bit (8051 JBCTest and clear bit (8051 JBCinstruction)instruction)


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In-line assembly

>ASM and ENDASM directivesare used along with

#pragma directives.


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Generating assembly source file

>#pragama src directive is used togenerate assembly code for C

program.


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Disabling interrupts

#pragma disableThis directive instructs the compiler

to disable the interrupt for the

duration of the function.


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Function parameters

By default c functions pass up tothree parameters in registers,theremaining in fixed memory

locations. Parameter passing in registers can

be disabled by calling #pragmaNOREGPARMS.


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Function parameters


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Return values


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