NRF52805 BLE and PWM

[MsaYpsomed]

Heija Guys,

I have a question regarding the usage of the Zephyr BLE and the PWM. I would like to use the Zephyr BLE Stack and the PWM Driver together. The Problem now is, that I get an Error, when I try to compile the project (cmake doesnt report a configuration issue). The Error is following:

the Line "BUILD_ASSERT(...)" is executed, because, as far as I understand, the BLE Stack uses the same PPI channels as the pwm driver. the question now is, can I change the PPI channels for the BLE stack or the PWM Driver, so that I can use both?

If yes: where do I need to change these channels?

if no: is there another way to use both?

Setup:

- Visual Code Studio as IDE ( I dont think that matters, but you never know..)

- zephyr version 2.4.99

- ncs Toolchain 1.5.1

- configured for board nrf52dk_nrf52805

- the prj.conf file looks kinda like this

# Bluetooth
CONFIG_BT=y
CONFIG_BT_LL_SW_SPLIT=y
CONFIG_BT_CTLR_TX_PWR_PLUS_4=y
CONFIG_BT_DEBUG_LOG=y
CONFIG_BT_DEVICE_NAME="BLE Device1"
CONFIG_BT_EXT_ADV=y
CONFIG_BT_CTLR_ADV_EXT=y
CONFIG_BT_CTLR_ADV_DATA_LEN_MAX=251

# Debug console
CONFIG_DEBUG_OPTIMIZATIONS=y

# Serial
CONFIG_SERIAL=n

# Segger RTT
CONFIG_PRINTK=y
CONFIG_USE_SEGGER_RTT=y
CONFIG_RTT_CONSOLE=y
CONFIG_UART_CONSOLE=n
CONFIG_LOG_BACKEND_RTT=n
CONFIG_LOG_BACKEND_UART=n

# PWM
CONFIG_PWM=y
CONFIG_PWM_NRF5_SW=y
CONFIG_PWM_LOG_LEVEL_DBG=y

thanks in advance for any help or tip!

[Carl Richard]

Hello!

Thanks for reaching out. I will take a look at this. In the meantime, may I ask why you're using a legacy driver and not nRFX? (since CONFIG_PWM_NRF5_SW is enabled)

Best regards,
Carl Richard

[MsaYpsomed]

Heija Carl,

thanks for your help. I got the driver configuration from the zephyr samples:

- BLE: beacon

- PWM: fade_led

I later found in a post, that they suggest using CONFIG_PWM_NRF5_SW for softwarebased pwm, since the NRF52805 does not have an hardware implemented pwm module.

Best regards,

Marc

[Carl Richard]

Hello again!

You can change the PPI base used by the SW PWM using a DTS overlay. In this case add the file "nrf52dk_nrf52805.overlay" to the project, containing the following code:

&sw_pwm {
    status = "okay";
    ppi-base = <10>;
};

This sets the "ppi-base" to 10, as the previous channels are used by the radio. 

One note. I see that you have enabled "CONFIG_BT_LL_SW_SPLIT=y", which forces the application to use the Zephyr Bluetooth LE controller. I did not see the error when using Nordic's Softdevice Controller (used by default on nRF5x devices), so you could consider doing that instead.

Best regards,
Carl Richard

[MsaYpsomed]

Heija Carl,

thanks for your answer. I could fix our problem with adding the ppi-base line. Infact We had to change it to

ppi-base = <11>

Now it works as intended.

Best regards,

Marc