limit the linux partition in DDR3 memory of DE1-SOC board

--- Quote Start ---

Using the cable ethernet not the uart can i use this command ?

--- Quote End ---

You can set these parameters from within uBoot, independently from your connection.

If you type "printenv" within uBoot you will see the entire environment variables. Probably you can spot some variables that are used for booting the kernel eg. name of the kernel image, boot parameters....

--- Quote Start ---

this command limit the linux to use just 800M of the DDR3 memory?

so to which adress i can write to ddr3 memory from the FPGA?

--- Quote End ---

You can verify this by typing

cat /proc/iomem

It should say something like "00000000-31ffffff : System RAM" and that is the memory range used by kernel. You can do with the rest whatever you want.