Cyclone III RAM usage

Altera_Forum · ‎08-31-2010

Hi,

i am using a Cyclone III EP3C40 FPGA with 126 M9K Blocks. In my Design there is a SOPC-System with 3 NIOS II CPUs. I assigned 28 / 24 / 48 kBytes of onchip-Memory to the three RAMs. The 24kByte-RAM uses 24 M9ks, the 48kByte RAM uses 48M9ks, but the 28k-Byte-RAM uses 32 M9Ks. Why? I tried to set the size to 26k-Byte, but there RAM also uses 32M9Ks then. Is there any setting or something about the resource usage?

Thanks in advance

Paddy

Altera_Forum · ‎08-31-2010

The megawizard and SOPC builder aren't always able to optimize properly the use of memory blocks when using a size that isn't a power of 2. You could use two memory blocks, one of 24k and another of 4k, and assign them consecutive addresses, but you'll need to use a custom link script if you want to use them as a single memory.

Altera_Forum · ‎08-31-2010

Look at the RAM summary report in the fitter. It will tell you how the individual memory blocks are configured so you can see how they are used to make up the composite memory.

Altera_Forum · ‎08-31-2010

Hi,

thanks for your reply.

I will try to split the memory and edit the linker-script.

Thanks, Paddy