i.MX RT1064 FlexRAM configuration (OCRAM amount)

[DashNode]

Hi.

I was reading Application Note AN12077 in order to properly configure the FlexRAM module on my i.MX RT1064 microcontroller.
I originally planned on using half (256 kB) of the FlexRAM banks as ITCM and the other half as DTCM (so no OCRAM bank in the FlexRAM at all, only the separate fixed 512 kB non-FlexRAM OCRAM will remain).
However I came accross this note in the document :

"The minimum configuration of OCRAM is 64 KB. This is
required due to ROM code requires at least 64 KB of RAM for its
execution. The minimum OCRAM requirements can be device dependent."

I understand that the boot ROM's code may need some OCRAM from the FlexRAM when running at startup.

But then, as soon as it jumps into the user's program image, the boot ROM code basically won't be executing again until the next device reboot,
so the user code should then have the freedom to configure the entire FlexRAM as it sees fit, right ?

I don't understand why the user code should preserve these FlexRAM OCRAM banks, while the boot code that needed them isn't even running anymore.
Can someone shed some light on the subject ?

Many thanks in advance.

[mjbcswitzerland · Accepted solution]

Hi

See the section 11 of https://www.utasker.com/docs/iMX/i.MX_RT_1064_uTasker.pdf
Applications can reconfigure the FlexRAM to use only DTC and ITC (with no OCR) without any issue - it has been done like this for a long time in numerous products that are based on the uTasker project which automatically configures the FlexRAM at run time to match the optimal application/data configuration so that code and data can operate with zero wait state.

If you want to jump to the ROM loader during operation it can be reconfigured to have some OCR but this has never been necessary (to date).

You might find that the FlexRAM setting is persistent across SW resets but that is not relevant when booting to Flash.

Regards

Mark