Are there any document about GAP and GATT BLE on Rapid IOT for sensors ? I would like to connect Rapid IOT from ESP32.
Do you mean something like this?
Creating a custom profile using NXP BLE stack – Server
How to create a Custom Profile - Client
If you look for further information regarding the BLE transmission protocol, I believe this link will also be helpful which it's some of the information available in the NXP knowledge-center.
Besides that, you can also check the Bluetooth® Low Energy Applications Developer’s Guide and the Bluetooth Low Energy API reference manual
These document seems to be targeting the KW41 chip. However, there isn't any SDK examples for the KW41 ("import SDK examples" shows an empty list after selecting KW41).
I want to create GATT characteristics to report sensor readings.
How can I use BLE from K64 chip, with the factory KW41 firmware? Or, if I have to program the KW41, is there a "hello_world" for me to get started?
As the KW41Z it's running a host controlled interface you could send the commands to work with the network, I believe there are quite useful posts and examples in the community such as these:
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Rapid IoT Kit - Wireless Uart Demo
If you still have any doubt after reading those, just let me know.
There is a project for KW41Z but not as "Example project", you have to import it from the file system, it is located under SDK path at SDK_2.2_RapidIoT_MKW41Z4\boards\rpk_kw41z\rapid_iot_apps\rpk_kw41z_hybrid
This is the default application flashed in KW41Z
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