nRF52805 Central not supported?

[droberson]

Hello,

We are evaluating MCU's for a low cost Central device that is extremely cost constrained. The nRF52805 and the nRF52810 both have the same RAM (24 KB) and FLASH (192 KB) size. Yet, the nRF52805 does not support the Central role but the nRF52810 does. With this in mind, I have a few questions:

1. Why does the nRF52805 not support the Central role even though the nRF52810 does?

I understand that the nRF52805 only supports SoftDevice S112 and S113, but what is stopping you from running S132 on the nRF52805?

2. If you can't run S132 on the nRF52805, does running nRF Connect SDK provide the use of the Central role on the nRF52805?

3. Do you have any Central role SDK examples running on the nRF52805? (nRF SDK or nRF Connect SDK)

4. If the nRF52805 can't run in Central mode, what is the lowest cost MCU that Nordic provides that supports the Central role?

Thanks,

Derek

[droberson]

Hey Einar,

Thanks for your reply. Do you have a similar prj_minimal.conf example for a Central device and the associated RAM and Flash usage? I imagine a Central example will use less resources since it doesn't have to allocate memory for characteristics, service, etc. Correct me if I am wrong.

Thanks,

Derek 

[Einar Thorsrud]

Hi Derek,

The numbers in my previous post is for a central sample, but the stack sizes were adjusted based on the config I linked to. If I run thread analyzer on the sample I ran you can see that there is still some room for optimization:

RX WQ : STACK: unused 424 usage 600 / 1024 (58 %); CPU: 6 %
BT TX : STACK: unused 40 usage 600 / 640 (93 %); CPU: 0 %
sysworkq : STACK: unused 1040 usage 496 / 1536 (32 %); CPU: 1 %
MPSL Work : STACK: unused 344 usage 296 / 640 (46 %); CPU: 0 %
idle : STACK: unused 64 usage 64 / 128 (50 %); CPU: 90 %
ISR0 : STACK: unused 672 usage 352 / 1024 (34 %)

But this depends on many factors and you normally want some margin, so I think the nubmer from my previous post is sensible (reasonable and not too optimistic).

[droberson]

Hey Einar,

Perhaps I am missing something, but the example you referenced is 'sdk-nrf/samples/bluetooth/peripheral_lbs/prj_minimal.conf'.

The project name is "Bluetooth: Peripheral LBS".

https://github.com/nrfconnect/sdk-nrf/tree/main/samples/bluetooth/peripheral_lbs 

The usage / "Testing" section of the paged linked above says:

"The device is advertising as 'Nordic_LBS'"

What am I missing?

Thanks,

Derek

[Einar Thorsrud]

Hi Derek,

Yes, that is correct. But the same configs are usable on central samples as well. And I tested with this central sample (the same as Helmut used), and the numbers I have pasted is from that sample.

[droberson]

Ohh I see, makes sense. You were just using the configuration from the Peripheral example and applying it to the Central example. Got it.

That answers my questions. Thanks!

Derek