I know C, I learned to build an Atmel example code for AT91SAM7X256 with Yagarto. However, I don’t know much about writing makefiles. I tried to modify various FreeRTOS demo projects for Yagarto and AT91SAM7X256 with no success. I would like to have a working toolchain and a simple FreeRTOS demo code, which compiles correctly. Does someone know such a project example in the net? Thank you.

There already is a makefile for the SAM7X that builds using Yagarto within the FreeRTOS.org .zip file.  You will find it in the FreeRTOSDemolwIP_Demo_Rowley_ARM7 directory.  Just navigate to that directory, then type "make". Regards.