InitFlash on F28069 controlSTICK

Anandhi Ramesh

We are evaluating the piccolo processor for our algorithm, and were running the whole program from RAM and profiling using the CCS profiler.

Then, we moved the .text section to Flash, and checked the cycle count using the clock. We found that the cycle numbers were almost 10 times the RAM count. After some basic checks, it turned out that we werent calling InitFlash in deviceSetup. So, after adding that call and ensuring the waitstates were set as per the TRM, we find that the performance ratio is about 1.5 (flash program takes about 1.5 times as many cycles as RAM did).

The question is, what was happening when we did not call InitFlash? Were those numbers meaningful in any sense? Also, is the number we are observing now reliable? Does putting the .text section in flash only take about 1.5 times as many cycles as running it entirely out of RAM? Is there any documentation comparing performance when running program out of flash or RAM on the piccolo devices?

Thanks,

Anandhi

over 12 years ago

0 Gautam Iyer over 12 years ago

Guru 192875 points

Hi,

Here is a doc you can go through:

2158.Running from Internal Flash.pdf

For increasing your flash performance, you can transfer few time critical functions to RAM while initializing using:

3733.Flash to RAM.pdf

Also check this out:

http://processors.wiki.ti.com/index.php/C2000_Flash_Common_Issues/FAQs#Code_Runs_Slower_in_Flash_than_RAM

Here is a reference thread:

http://e2e.ti.com/support/microcontrollers/c2000/f/171/t/208095.aspx

Regards,

Gautam

0 Anandhi Ramesh over 12 years ago in reply to Gautam Iyer

Prodigy 130 points

Hello Gautam,

Thanks for the links, ill check them out. That thread looks almost intimidating in its detail. I did look through 2158 before posting this query though.

In order to satisfy the basic reason for the query - can i expect that code run from flash will be consistently X times slower than if it is run from RAM? And what would X be? I can see that currently its about 50% more cycles for flash programming. Does this normally apply given a 90MHz 28069 processor with internal flash waitstates se to 3,3,5 as mentioned in TRM?

thanks,

anandhi

0 Brett Larimore over 12 years ago in reply to Anandhi Ramesh

TI__Guru 57255 points

Hi Anandhi,

There isn't a strict definition for the 'X' you describe. In most application code we see about 10% - 20% improved performance when code is run in RAM as opposed to FLASH.

C2000 devices' flash utilizes a prefetch buffer (when enabled) which is why the performance of flash is as good as it is. If your code is linear you will get very good FLASH performance and will perform worse under code that is full of branches. Without running InitFlash you may not have had the prefetch buffer enabled (ENPIPE) and may have also gotten stuck with the default 15 waitstates for the flash which are quite a bit higher than what the TRM will allow (thereby making the code run slower).

The following post also describes more about the prefetch mechanism:
http://e2e.ti.com/support/microcontrollers/c2000/f/171/p/299489/1044089.aspx#1044089

Another nice post if you're looking at the waitstates on the F28069:
http://e2e.ti.com/support/microcontrollers/c2000/f/171/p/285606/996225.aspx#996225

Good luck on your project!

Thank you,
Brett

C2000™︎ microcontrollers

C2000 microcontrollers forum

InitFlash on F28069 controlSTICK