portSTACK error with ATmega2560

I am working with atmega2560 & freeRTOS. While compiling the code of FreeRtos4.1.0, it was asked for various header files like freertos.h and freertosconfig.h etc. Then on including all files, error of header file not found has removed. But it gives other error of "portSTACK_Type" and  "portBASE_Type" are undeclared in "portable.h". I face the same problem in AVR studio and IAR Embedded workbench. This is my very first time approaching with Free RTOS and also with AVR. So kindly help.

portSTACK error with ATmega2560

There are a couple of things you need to do…first have the correct include paths and second have the correct port definition. Demo projects are included in the download for AVR using both GCC and IAR.  To create a new project take one of these demos as a starting point.  Once the demo is compiling (should compile straight off) you can remove the demo app files and add in your app files. When building with GCC GCC_MEGA_AVR must be defined.  When building with IAR IAR_MEGA_AVR must be defined.