nRF54l15 Custom Board & nRF21540 FEM & nRF7001 GPIOTE error

RE: nRF54l15 Custom Board & nRF21540 FEM & nRF7001 GPIOTE error

Hieu — Mon, 23 Mar 2026 14:11:46 GMT

While I am quite curious why you got the compilation error, PaKa raised a key point.

Sharing SPI bus between the FEM and another device won't work well. I don't know much about the nRF70x products, but the timing requirement for controlling the nRF21540 is very strict, so the tiniest delay due to sharing bus can cause failures.

Therefore, we strongly recommend against sharing the same SPI bus between nRF7001 and nRF21540.

If you already have a hardware designed, then you could consider controlling the nRF21540 only over GPIO instead.

RE: nRF54l15 Custom Board & nRF21540 FEM & nRF7001 GPIOTE error

PaKa — Mon, 23 Mar 2026 08:47:42 GMT

To be clear:

The nRF21540 control should be on a dedicated SPIM in the peripheral domain and the pins should be on Port 1. This is what is validated on our side.

Both sharing SPIM and using port 2 are issues in this setup.

Using port 2 is not OK as you will have extra delays due to cross domain connections and thus you will also need to run with constlat enabled as stated in the datasheet.

RE: nRF54l15 Custom Board & nRF21540 FEM & nRF7001 GPIOTE error

Dawson — Fri, 20 Mar 2026 17:20:04 GMT

For reference here is my SPI pin definitions

/* Shared SPI master bus for nRF70 (CS1) and nRF21540 FEM (CS2) */
spi21_default: spi21_default {
group1 {
psels = <NRF_PSEL(SPIM_SCK, 2, 6)>,
<NRF_PSEL(SPIM_MOSI, 2, 8)>,
<NRF_PSEL(SPIM_MISO, 2, 9)>;
};
};

RE: nRF54l15 Custom Board & nRF21540 FEM & nRF7001 GPIOTE error

Dawson — Fri, 20 Mar 2026 17:10:35 GMT

I thought that since I used spi21 and the cs for the nRF21540 is on port 1 that this would be fine.
To be clear are you saying that the issue is that SPIM_SCK, SPIM_MISO, SPIM_MOSI are on Port 2 or is the issue that I am trying to share the SPI with the nRF7001 and need a sperate dedicated SPI with all of the SPI pins on Port 1?

RE: nRF54l15 Custom Board & nRF21540 FEM & nRF7001 GPIOTE error

Dawson — Fri, 20 Mar 2026 16:53:06 GMT

devzone.nordicsemi.com/.../nRF21540_5F00_Shared_5F00_SPI_5F00_Example.zip
Here is example of this currently in not compiling state described above.

RE: nRF54l15 Custom Board & nRF21540 FEM & nRF7001 GPIOTE error

PaKa — Fri, 20 Mar 2026 13:00:57 GMT

Hi,

If you are going to use the SPI on the nRF21540 to control the gain/output power on the FEM then it has to be on a dedicated SPI module. This is required to meet the timing requirements of the FEM as MPSL needs extremely tight control of the timing to meet the stack requirements. If the SPI is in use to communicate with the nRF7001 when you try to use the nRF54L15 radio then it would crash..

From the FEM documentation for the SDK:

On nRF54L Series devices, use SPI bus instance belonging to the PERI Power Domain (on the nRF54L15 SoC one of the spi20, spi21, spi22 instances). Select the pins for the SPI interface that belong to the same power domain as the SPI bus instance. This is Port 1 for the nRF54L. All pins on the same port to guarantee timing

RE: nRF54l15 Custom Board & nRF21540 FEM & nRF7001 GPIOTE error

Hieu — Fri, 20 Mar 2026 09:45:03 GMT

Hi Dawson,

Looking at the SDK source file doesn't help explain what is wrong. I will have to reproduce this and debug further.

If you have a minimal sample, that would help speed thing up a lot. Otherwise, I will return when I find something.

Hieu