Issue using enabled cache and TLS with iMXRT1051

[KarenMczm]

Hi, 

I am working on an MQTT round-trip test and I want to improve my performance, I tried enabling the D-Cache and the times improve with TCP port but when I tried with TLS the connection is lost, I read about the coherency problem, so I moved the mbedtls library into a non-cacheable region but the problem still present.

Regards,

[KarenMczm]

Thanks for the reply, I did the following changes in the code and the linker file to place mbedTLS into non-cached memory.

Thanks,

Karen

[victorjimenez]

Hello Karen, 

The OCRAM is handled differently than the DTCM and ITCM memories. What happens if you place the mbedTLS into either the DTCM or ITCM? 

Regards,
Victor

[KarenMczm]

Hi Victor,

I already solved the issue by moving the lwip library into the non-cacheable region as shown in the following image:

I tested with the mbedtls library in the non-cacheable region and outside of it. In both cases, it works, but if I put mbedtls in the non-cacheable region, the round trip using TLS is a bit slower than if I just leave lwip in the non-cacheable region.

Thanks for the support,

Karen

[victorjimenez]

Hello Karen, 

In which memory specifically are you placing the mbedtls library? To work with mbedTLS, you need to place the mbedTLS heap allocator in a non-cached memory that can be accessed by the DCP. 

Also, you might find useful the following application note:

Using the i.MXRT L1 Cache (nxp.com)

Regards,
Victor