nRF52 cache

RE: nRF52 cache

tesc — Thu, 07 Jul 2016 12:10:20 GMT

Hi.

Just wanted to add that in the nRF52832 Product Specification the section CPU performance lists the following numbers for CPU wait states when running from flash and RAM:

flash w/o cache: min. 0 max. 2
flash w/ cache: min. 0 max. 3
RAM: max. 0

The best and worst case numbers for flash access are due to difference in frequency between CPU and flash. This means flash reading times are in the range 0 to 2 cpu cycles without cache, and in the range 0 to 3 cpu cycles including a cache miss.

Regards, Terje

RE: nRF52 cache

jsleeman — Wed, 15 Jun 2016 10:53:32 GMT

Hi. It's not essential but it would be useful as our timings are very tight, and it would be good to work out how much time everything is taking. Thanks.

RE: nRF52 cache

Anders Strand — Wed, 15 Jun 2016 07:16:52 GMT

Hi. The flash reads will be as fast as RAM reads. I could not find any numbers at this time, but you can assume it to be very fast. Will you need the excact numbers?

RE: nRF52 cache

jsleeman — Tue, 14 Jun 2016 13:19:36 GMT

The webpage you have provided a link to, provides timings for write, erase page and erase all, however nothing is mentioned about write times. Is it missing from the webpage? Or could you point out something i could search for in the page to help me find it. Many thanks, James.

RE: nRF52 cache

Anders Strand — Tue, 14 Jun 2016 13:06:37 GMT

When using a softdevice, it will turn on the Cache by default. The application is free to turn it off if it wants.

Cache will in most applications bring a performance increase. Spending less time waiting for flash operations will in most cases also decrease the current consumption of an application.

Information about the flash and cache can be found here. Here you can see timings of flash reads and writes.

RE: nRF52 cache

jsleeman — Tue, 14 Jun 2016 12:08:49 GMT

Hi Anders, thanks for getting back to me. The issue has been further investigated at our end, it was been found that when a part of the system is sped up it fails in a very similar way to what we were finding when the performance was worse. The performance was remeasured and it has been found to increase when the cache is switched on. So the cache is not an issue.

When we were trying to calculate the rough performance gains we should see when enabling the cache, we looked at the datasheet to try and see the time it takes to perform a flash read. We couldn't find this information, is this available? Thanks again, James.

RE: nRF52 cache

Anders Strand — Tue, 14 Jun 2016 09:31:07 GMT

How are you measuring the performance with and without cache enabled? I will look into this in the meantime