nrf9160 using pin 29 as spi chip select

[Mike Jongen]

We are trying to connect the nrf9160 to a spi flash device. we have a custom board with the following pins connected:

sck: 27

mosi: 28

miso: 30

cs: 29

wp: 31

reset: 26

For the testing, we are using the drivers/spi_flash sample of zephyr.

we use the following overlay:

&spi3 {
    compatible = "nordic,nrf-spim";
    status = "okay";
    sck-pin = <27>;
    mosi-pin = <28>;
    miso-pin = <30>;
    cs-gpios = <&gpio0 29 GPIO_ACTIVE_LOW>;

    s25fl128l: s25fl128l@0 {
        compatible = "jedec,spi-nor";
        label = "S25FL128L";
        reg = <0>;
        jedec-id = [01 60 18];
        spi-max-frequency = <200000>;
        wp-gpios = <&gpio0 31 GPIO_ACTIVE_LOW>;
        reset-gpios = <&gpio0 26 GPIO_ACTIVE_LOW>;
        size = <0x4000000>;
        has-dpd;
        t-enter-dpd = <4000>;
        t-exit-dpd = <25000>;
        has-be32k;
    };
};

&uart0 {
	status = "disabled";
	current-speed = <115200>;
	tx-pin = <25>;
	rx-pin = <24>;
	rts-pin = <23>;
	cts-pin = <22>;
};

&i2c2 {
	compatible = "nordic,nrf-twim";
	status = "disabled";
	sda-pin = <21>;
	scl-pin = <20>;
};

We have disabled the uart and i2s that use these pins in the default design.

To communicate with the nrf9160, we use RTT. We use the following configuration:

CONFIG_STDOUT_CONSOLE=y
CONFIG_FLASH=y
CONFIG_SPI=y

# Enable printing
CONFIG_SERIAL=y
CONFIG_PRINTK=y
CONFIG_CONSOLE=y
CONFIG_STDOUT_CONSOLE=y

# Enable log
CONFIG_LOG=y

# Enable rtt
CONFIG_USE_SEGGER_RTT=y

# Enable rtt shell
CONFIG_SHELL=y
CONFIG_SHELL_BACKEND_RTT=y

# Switch console to rtt, for print statements
CONFIG_UART_CONSOLE=n
CONFIG_RTT_CONSOLE=y

The sample prints the following code:

JEDEC SPI-NOR SPI flash testing
==========================
SPI flash driver S25FL128L was not found!

When checking the signals with a scope, we noticed that the chip select (pin 29) does not have its expected behavior. Instead of becoming active during spi commands, continually switches between high and low, and looks like some sort of serial data.

We have tried to toggle the pin as an gpio, but are unable to control this pin.

We have tried a hello_world sample (without spi/flash), and notice the same behavior on pin 29. 

Since our code does not use pin 29 for anything except chip select, we suspect that another program (bootloader? SPM?) configures the pin as an uart, preventing us the use it as a chip select.

Do you know if this assumption is correct, and how we could test and fix this? Or is there another solution to the problem? 

[Øyvind]

Hi, 

Have you configured the CS pin in your overlay file?

Kind regards,
Øyvind

[Mike Jongen]

Yes, see line 7 of the overlay I have included.

[Øyvind]

Thanks for updating with that information. The overlay file looks good. I agree that it seems that pin 29 might be configured to something else. Can you provide zephyr.dts from the build folder? Are you running a custom board, or the nRF9160 DK or Thingy:91?

-Øyvind

[Mike Jongen]

Here is the zephyr.dts:
zephyr.dts

The board is a custom board.

[Øyvind]

You were right, this is the SPM causing issues on UART0. 

Have a look at this solution: 
https://devzone.nordicsemi.com/f/nordic-q-a/55667/nrf9160-disable-bootloader-and-spm-uart-console-print

[Mike Jongen]

I have tried the solution without success.

My CMakeLists.txt is now:

cmake_minimum_required(VERSION 3.13.1)
find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
project(spi_flash)

set(spm_CONF_FILE
    prj.conf
    $(CMAKE_CURRENT_LIST_DIR)/spm.conf
    )

FILE(GLOB app_sources src/*.c)
target_sources(app PRIVATE ${app_sources})

spm.conf is:

CONFIG_SERIAL=n
CONFIG_STDOUT_CONSOLE=n
CONFIG_LOG=n
CONFIG_BOOT_BANNER=n
CONFIG_PRINTK=n

CONFIG_SPM_BOOT_SILENTLY=y

This is the waveform that is send over pin 29 at startup:

pin_29_waveform.zip

I have tried the flash example, and tried to toggle pin 29 as gpio. both failed.

[Øyvind]

Can you try this instead:

cmake_minimum_required(VERSION 3.13.1)

set(spm_CONF_FILE
    prj.conf
    $(CMAKE_CURRENT_LIST_DIR)/spm.conf
    )
    
find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
project(spi_flash)

FILE(GLOB app_sources src/*.c)
target_sources(app PRIVATE ${app_sources})

[Mike Jongen]

Thank you, I am now able to control the pins as gpio. The flash example still gives the same output, so I'll have to see if something else is wrong. 

Small note, I had to use ${CMAKE_CURRENT_LIST_DIR} instead of $(CMAKE_CURRENT_LIST_DIR), in case anyone has issues with the CMake.

[Øyvind]

Mike Jongen said:

Small note, I had to use ${CMAKE_CURRENT_LIST_DIR} instead of $(CMAKE_CURRENT_LIST_DIR), in case anyone has issues with the CMake.

 Thanks for the note! That's one detail that went right past me in my last reply. 
 

Mike Jongen said:

The flash example still gives the same output, so I'll have to see if something else is wrong. 

Assuming you mean it prints the  output "SPI flash driver S25FL128L was not found!"? Or do you mean the output on pin 29?

Have you actually added the drivers for this device? I am not able to find this device in Zephyr

[Mike Jongen]

No, it is a standard spi nor flash, and doesn't require a specific driver. I just needed to set SPI_NOR.

This is the final conf:

CONFIG_STDOUT_CONSOLE=y
CONFIG_SPI=y
CONFIG_SPI_NOR=y
CONFIG_FLASH=y

# enable printing
CONFIG_SERIAL=y
CONFIG_PRINTK=y
CONFIG_CONSOLE=y
CONFIG_STDOUT_CONSOLE=y

# Enable log
CONFIG_LOG=y

# Enable rtt
CONFIG_USE_SEGGER_RTT=y

# Enable rtt shell
CONFIG_SHELL=y
CONFIG_SHELL_BACKEND_RTT=y

# Switch console to rtt, for print statements
CONFIG_UART_CONSOLE=n
CONFIG_RTT_CONSOLE=y

The flash example now works, thanks for the help!