Quality RTOS & Embedded Software

 Real time embedded FreeRTOS RSS feed 
Real time embedded FreeRTOS mailing list 
Quick Start Supported MCUs PDF Books Trace Tools Ecosystem TCP & FAT Training




Loading

Why FreeRTOS defines heapSTRUCT_SIZE as a const variable rather than a macro?

Posted by realsil on April 13, 2015

I find headSTRUCTSIZE is defined as a const variable, but my compiler always optimizate it. I have check the disassemble file os heap5.o, and I found the code "puc -= heapSTRUCT_SIZE;" is translated into "SUBS r4,r4,#8" automatically.

Is there any difference between "define heapSTRUCT_SIZE as a const variable" and "define heapSTRUCT_SIZE as a macro"?

static const uint16t heapSTRUCTSIZE = ( ( sizeof ( BlockLinkt ) + ( portBYTEALIGNMENT - 1 ) ) & ~portBYTEALIGNMENTMASK );

void vPortFree( void *pv , RAMTYPE ramType) { uint8t *puc = ( uint8t * ) pv; BlockLinkt *pxLink;

 if( pv != NULL )
 {
            /* The memory being freed will have an BlockLink_t structure immediately
            before it. */
            puc -= heapSTRUCT_SIZE;

            /* This casting is to keep the compiler from issuing warnings. */
            pxLink = ( void * ) puc;

/* ignore some lines */ }

vPortFree PROC PUSH {r4-r6,lr} MOV r5,r1 MOV r4,r0 CMP r0,#0 BEQ |L1.720| SUBS r4,r4,#8


Why FreeRTOS defines heapSTRUCT_SIZE as a const variable rather than a macro?

Posted by davedoors on April 13, 2015

If you use a macro with low or no compiler optimization it will be calculated each time it is used. If you use a const then it is calculated when you compile the program.


Why FreeRTOS defines heapSTRUCT_SIZE as a const variable rather than a macro?

Posted by realsil on April 13, 2015

Dear Dave,

I think the fact is always the opposite. If we use a const and close the compiler's optimization, some variable reference this const may calculated everytime when program run.


[ Back to the top ]    [ About FreeRTOS ]    [ Sitemap ]    [ ]




Copyright (C) 2004-2010 Richard Barry. Copyright (C) 2010-2016 Real Time Engineers Ltd.
Any and all data, files, source code, html content and documentation included in the FreeRTOSTM distribution or available on this site are the exclusive property of Real Time Engineers Ltd.. See the files license.txt (included in the distribution) and this copyright notice for more information. FreeRTOSTM and FreeRTOS.orgTM are trade marks of Real Time Engineers Ltd.

Latest News:

FreeRTOS V9.0.0 is now available for download.


Free TCP/IP and file system demos for the RTOS


Sponsored Links

⇓ Now With No Code Size Limit! ⇓
⇑ Free Download Without Registering ⇑


FreeRTOS Partners

ARM Connected RTOS partner for all ARM microcontroller cores

Renesas Electronics Gold Alliance RTOS Partner.jpg

Microchip Premier RTOS Partner

RTOS partner of NXP for all NXP ARM microcontrollers

Atmel RTOS partner supporting ARM Cortex-M3 and AVR32 microcontrollers

STMicro RTOS partner supporting ARM7, ARM Cortex-M3, ARM Cortex-M4 and ARM Cortex-M0

Xilinx Microblaze and Zynq partner

Silicon Labs low power RTOS partner

Altera RTOS partner for Nios II and Cortex-A9 SoC

Freescale Alliance RTOS Member supporting ARM and ColdFire microcontrollers

Infineon ARM Cortex-M microcontrollers

Texas Instruments MCU Developer Network RTOS partner for ARM and MSP430 microcontrollers

Cypress RTOS partner supporting ARM Cortex-M3

Fujitsu RTOS partner supporting ARM Cortex-M3 and FM3

Microsemi (previously Actel) RTOS partner supporting ARM Cortex-M3

Atollic Partner

IAR Partner

Keil ARM Partner

Embedded Artists