NRF5340 Performance

[DaveElam]

Hello, we are a long time user of the NRF52840 and are consistently running out of spare CPU, so are looking at the NRF5340.

I see that the NRF5340 runs up to 128Mhz.  Was the flash memory bus bandwidth doubled vs the NRF52? Also does the SRAM run up to 128Mhz?

Thanks,

Dave

[ovrebekk]

Hi Dave

I would have to check if the flash bandwidth has increased, but the main advantage over the nRF52 is that the cache efficiency is increased significantly. 

For this reason, if you look at the Coremark numbers the nRF53 application core is noticeably more powerful even at the same clock frequency, and you get more than double the performance when running at 128MHz. 

And then you have the network core on the side, which alone provides comparable performance to the nRF52840.

For the application core half the RAM runs at full speed, but the upper 256kB of the RAM is slower. For this reason it is recommended to use the upper part of the RAM for peripheral buffers (SPI, UART, QSPI etc). 

Best regards
Torbjørn

[KevinA]

Faster and beside the XIP QSPI the regular SPI has an additional control, D/C, a signal used by eDisplay  devices to signify Data or Control, Zephyr supports eDisplays.   

[DaveElam]

Hi, did you get a chance to check on whether the Flash memory bandwidth doubled?  If not, this won't provide us much of a performance boost over the NRF52  Caching alone won't much with our application.

[ovrebekk]

Hi Dave

Sorry about that, I forgot to follow up on this one. 

I have forwarded your request to the experts and will let you know once I hear back from them. 

Either way, how can you be so sure that high flash bandwidth is required for your particular application? 
Are you running a large code base with extensive branching that is known to be inefficient when using cache? 

The best way to know for sure would obviously be to acquire a nRF5340DK and do some benchmarking on your own, to verify the performance when running your particular algorithms. 

Best regards
Torbjørn

[DaveElam]

Hi Torbjorn,

Caching of course will have some impact, but in general on most applications, doubling CPU speed and doubling power consumption is not worth it with a caching improvement of say 20%.  This is a common mistake most controller companies make in their design.  In our case, our main loops are not small enough to be fully cached.  I can't say much more than that.  And it's probably safe to assume that this same rule applies to most of your customers considering in the majority of the projects I have worked on, that is the case.  ARM doesn't seem to understand this, and we may not be using an ARM much longer.  Companies like Renesas seem to understand this problem, and properly scaled their memory bandwidth to run from flash at full speed.  Admittedly, not everyone needs this performance, but most studies have shown that running as fast as possible and then going to sleep is the most power efficient way of operating. This makes the sole reliance on caching to balance the CPU speed increase contrary to good design practices.

Thanks,

Dave