What is actual size required for scratch area for CCM on nrf52?

RE: What is actual size required for scratch area for CCM on nrf52?

Torsten Robitzki — Wed, 07 Nov 2018 08:23:41 GMT

I found this thread, because I was running in the same Problem. BTW: the term MAXPACKETSIZE is used exactly once in the documentation. So I understood it to be the maxium packet size, not the maximum value that could be stored in the length field.

RE: What is actual size required for scratch area for CCM on nrf52?

Kevin — Mon, 20 Feb 2017 18:20:06 GMT

Thank you Bjorn!

RE: What is actual size required for scratch area for CCM on nrf52?

bjorn-spockeli — Thu, 16 Feb 2017 15:15:57 GMT

Yes, that is correct. When using 8-bit mode of CCM (MODE = LENGTH_EXTENDED), the size of the SCRATCH area will be 267 bytes.

RE: What is actual size required for scratch area for CCM on nrf52?

Kevin — Thu, 16 Feb 2017 11:20:13 GMT

Hello, I got the same problem and I'm encrypting packet of length 13. The scratch pointer is written on 267 bytes for me too. Is it normal? Can you confirm that SCRATCH DATA area size correspond to maximum value of length field = 255 (in the case i am using a 8bit length field) + 16 bytes? you can see more information on my problem on my post : devzone.nordicsemi.com/.../

ps: i am using NRF52832-QFAA80XXXX

RE: What is actual size required for scratch area for CCM on nrf52?

will — Tue, 12 Apr 2016 16:13:46 GMT

Thanks Bjorn. It would be good to know the exact amount.

RE: What is actual size required for scratch area for CCM on nrf52?

bjorn-spockeli — Tue, 12 Apr 2016 13:50:54 GMT

Yes, we have seen this before and it may be an error in the Product Specification. It has been pointed out that the number of bytes must be reserved in RAM should be 16 + MAXPACKETSIZE bytes.

I have reported this internally and will update my answer as soon as I hear back from R&D.

-Bjørn

UPDATE 13.04.16:

Confirmed by R&D that the number of bytes that must be reserved in RAM should be 16 + MAXPACKETSIZE bytes. This will be fixed in the in the next revison of the nRF52832 Product Specification.