How to write Port.c in FreeRTOS

jj1010 wrote on Saturday, October 11, 2014:

I create a new project use port.c file which in the Demo project, and run sucessful with STM32 microcontroller. Now I want to write port.c file, how can I get technical support about writting port.c file, or which tutorial can help me. I find nothing in FreeRTOS website, only simply descriptioins.

Hope you help! Thanks.

rtel wrote on Saturday, October 11, 2014:

Which target do you want to create the port for?


jj1010 wrote on Sunday, October 12, 2014:

ARM Cortex-M3 architecture. I know there preparation of a good port.c in Demo Project.

If there is a language to express the meaning is not clear, ask me. My mother tongue is not English.

rtel wrote on Sunday, October 12, 2014:

The Cortex-M3 port will run on all Cortex-M3 device, from all
manufacturers - you do not need to write a port.c if you want to run on
a Cortex-M3.

To use a Cortex-M3 or a Cortex-M4 without FPU use the files in:

To use a Cortex-M4 with an FPU use the files in:


jj1010 wrote on Monday, October 13, 2014:

But I really would like to write port.c file.

And if I use a new architecture microcontroller which FreeRTOS does not support, how can I do?

davedoors wrote on Monday, October 13, 2014:

Look in portable.h, the functions that are defined in there need to be implemented in port. There are lots of port.c files you can use as examples.

The first thing you will need to do is work out what makes up the architecture context. List out the registers, and decide how they will be placed on the stack. The architecture will dictate some of that if some registers are pushed on to the stack manually.

Once you have a function that creates the starting stack for a task, create a function that starts the first task. Again there are lots of examples, and how it can be done is dictated by the architecture. Sometimes a simple function call is all that is needed, but sometimes a software trap is needed. The function moves the stack pointer to the start of the stack created for the task, then pops the registers off the stack into the architecture registers until finally it pops the program counter. The program counter will hold the address of the task function, so popping that address into the program counter will result in a jump to the start of the task.

Then you need to work out how you are going to switch between tasks. But one thing at a time.

There are some old pages here