i.MXRT FlexRAM size not being power of two and GPR14

[jdj]

I have a working configuration with FlexRAM as 256 kiB DTCM, no ITCM, 256 kiB OCRAM. I would like to use sizes which are not power of two (eg. 384 kiB DTC). My question is with regards to IOMUXC_GPR_GPR14.

AN12077 states that, in this case:

It is required to keep the default TCM size setting in the CM7_CFGxTCMSZ fields in the IOMUXC_GPR_GPR14 register (it considers the value of the whole FlexRAM size).

But the reset value of those fields is 0 - meaning no DTCM or ITCM. What is the default value mentioned in the AN? Is it setting both to 128 kiB? Or is it, as "it considers the value of the whole FlexRAM size" seems to indicate, setting both fields to 512 kiB (0b1010)? The last seems to make the most sense.

[jeremyzhou]

Hi,

Thank you for your interest in NXP Semiconductor products and for the opportunity to serve you.
1) What is the default value mentioned in the AN?
-- 512 KB, in another word, the value of the whole FlexRAM size.
Have a great day,
TIC

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[jdj]

Thank you for the answer. Is there any downside to setting it lower, as long as it's larger than what's actually configured? Say, having 96 kiB of ITCM and setting `CM7_CFGITCMSZ` to 128 kiB?

[jeremyzhou]

Hi,
1) Is there any downside to setting it lower, as long as it's larger than what's actually configured? Say, having 96 kiB of ITCM and setting `CM7_CFGITCMSZ` to 128 kiB?
-- CFGITCMSZ/CFGDTCMSZ bits determine the maximum of accessible address space, so it'll waste space after setting a lower value.
Hope this is clear.
Have a great day,
TIC

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