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


PIC18: service multiple interrupts

Posted by Paul_Piak on January 9, 2007

Since the PIC18 is pretty low-end, I like to make the code as efficient as possible.

The situation is as follows:
I usually use interrupts for i2c or serial communication, so typically I call xQueueReceiveFromISR and xQueueSendFromISR, which take relatively long to execute.
It is therefore quite likely that during handling of 1 interrupt, another interrupt fires.
In the PIC18 port, only 1 interrupt flag will be serviced every entry into the interrupt handler, each calling portSAVE_CONTEXT and portRESTORE_CONFIG.
I counted the number of instructions for a portSAVE_CONTEXT, which is about 100.
A portRESTORE_CONFIG takes the same amount of cycles. This is a lot of overhead.

I would like to move the calls to portSAVE_CONTEXT and portRESTORE_CONFIG from the interrupt functions to the interrupt handler prvLowInterrupt in port.c, so that portSAVE_CONTEXT is called once, all interrupts are served, forcing taskswitches etc. until the global interrupt flag drops (no interrupts to be served any more), (maybe even only 1 final 'yield'?) and then portRESTORE_CONFIG is called
My question is: Is there a fundamental problem with this? For example: is it possible to have the wrong task activated after this?



[ 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