topic Re: KW36 - how to receive GFSK custom frame in Kinetis Microcontrollers

KW36 - how to receive GFSK custom frame

adrian_chmiel — Wed, 20 May 2020 20:53:36 GMT

Hi,

I would like to communicate with LT8920 chip:

https://www.deviationtx.com/media/kunena/attachments/7714/LT8920datasheetEngversion201701191.pdf

It's a 2.4GHz GFSK radio, with frame look like that:

Is it possible to set something like that?

I checked documentation of KW36 and for example maximum SYNC lenght is 32bit.

So maybe is possible to receive GFSK data not in packets? Like RAW data, like sniffer?

If yes, how to do that?

Re: KW36 - how to receive GFSK custom frame

Sebastian_Del_Rio — Thu, 21 May 2020 20:59:12 GMT

Hi Adrian, I hope you're doing well!

There's a GFSK stack macro defined as gGenfskRawPacket which changes the packet type to transmit and receive information using a "RAW" format, instead of the regularly formatted GFSK packets. These have a maximum size of 35 bytes, which can contain the whole frame you describe. As an important note, the maxBufLengthBytes size for the Rx modes has to be set exactly to the size of the packet you're receiving, otherwise, it will be rejected.

There's also the MSK radio mode, which also bypasses all hardware acceleration, and allows for a maximum packet size of 35 bytes.

These modes have some important additional notes, which can be found on section 6.1.5 of the Generic FSK Link Layer Quick Start Guide document, included with the KW36's SDK, in the following path:

<…\SDK_2.2.3_FRDM-KW36\docs\wireless\GENFSK\Generic FSK Link Layer Quick Start Guide.pdf>

Please let me know if you need any more information.

Take care, best regards,

Sebastian

Re: KW36 - how to receive GFSK custom frame

adrian_chmiel — Fri, 22 May 2020 07:16:50 GMT

Thank you for your response.

So, in RAW mode I load info buffer the whole frame with the preamble etc. ? The same situation when i receive data, in buffer I will find preamble, data, crc etc?

I'm worried about info:

"maxBufLengthBytes size for the Rx modes has to be set exactly to the size of the packet you're receiving, otherwise, it will be rejected."

Does it mean that I need to know exactly what frame length I should expect?

If I set frame too long, will it also be rejected? Will not be filled with 0, 1 or random data (noise)?

If yes, I think the main problem can be with TRAILER in LT8920, because it have only 4bit, so whole frame have for example 22 bytes and 4 bits. Then MK36 radio cannot receive it?

Best regards

Adrian

Re: KW36 - how to receive GFSK custom frame

Sebastian_Del_Rio — Fri, 22 May 2020 15:26:31 GMT

Hi Adrian,

To my understanding, the 4bit trailer should be considered a full byte for the buffer size calculation so that it doesn't get rejected.

As another thing of note, according to section 6.1.1, the preamble and address size do not count against the 35 bytes allowed for RAW mode Rx and Tx.

With these considerations in mind, the KW36 should be able to receive the RAW packages.

Please let me know if you need any more information.

Take care, best regards,

Sebastian