Help with modem driver writing

[Captainfl4me]

Hello,

I'm trying to write a driver for a custom new NB-IoT chip (as part of a university project). I've write some of the required file for this to work: dts bindings, shields support (for easier overlay), Kconfig modem configuration file and I'm writing the C skeleton file to try having compiling driver without the logic at first. I would like to have basic working modem_shell capability before doing proper net offloading.

However, I'm stuck on a linking error when building my test app Undefined initialization levels used. This seems to be related to wrong device_tree or init function registering but cannot find the real root cause of this. Any ideas or documentation that could help me ?

Here is the files I used:

Fork Zephyr

• drivers/modem/Kconfig.st87m01

config MODEM_ST87M01
	bool "ST87M01 modem driver"
	select MODEM_RECEIVER
	select NET_OFFLOAD
	imply GPIO
	help
	  Choose this setting to enable ST87M01 NB-IoT modem driver.

if MODEM_ST87M01
	config MODEM_ST87M01_INIT_PRIORITY
	int "ST87M01 driver init priority"
	default 80
	help
	  ST87M01 device driver initialization priority.
	  Do not mess with it unless you know what you are doing.
	  Note that the priority needs to be lower than the net stack
	  so that it can start before the networking sub-system.

• drivers/modem/st87m01.c

#include <zephyr/logging/log.h>
#include <zephyr/net/net_if.h>
#include "st87m01.h"

LOG_MODULE_REGISTER(modem_st87m01, CONFIG_MODEM_LOG_LEVEL);

/*
 * Initializes modem handlers and context.
 * After successful init this function calls
 * modem_setup.
 */
static int modem_init(const struct device *dev)
{
	int ret = 0;
	ARG_UNUSED(dev);
	LOG_DBG("ST87M01 Init");

	mctx.data_manufacturer = mdata.mdm_manufacturer;
	mctx.data_model = mdata.mdm_model;
	mctx.data_revision = mdata.mdm_revision;
#if defined(CONFIG_MODEM_SIM_NUMBERS)
	mctx.data_imei = mdata.mdm_imei;
	mctx.data_imsi = mdata.mdm_imsi;
#endif
	mctx.data_rssi = &mdata.mdm_rssi;

	ret = mdm_receiver_register(&mctx, MDM_UART_DEV, mdm_recv_buf, sizeof(mdm_recv_buf));
	if (ret < 0) {
		LOG_ERR("Error registering modem context: %d", ret);
		goto error;
	}

	modem_reset();

error:
	return ret;
}

static void modem_reset(void)
{
}

/* Setup the Modem NET Interface. */
static void offload_iface_init(struct net_if *iface)
{
}

/* Register device with the networking stack. */
NET_DEVICE_DT_INST_OFFLOAD_DEFINE(0, modem_init, NULL, &mdata, NULL, MODEM_ST87M01_INIT_PRIORITY,
				  &api_funcs, MDM_MAX_DATA_LENGTH);

-drivers/modem/st87m01.h

#include <zephyr/kernel.h>
#include <zephyr/sys/ring_buffer.h>
#include <zephyr/device.h>
#include <zephyr/devicetree.h>

#include <zephyr/net/net_context.h>
#include <zephyr/net/net_if.h>
#include <zephyr/net/net_offload.h>
#include <zephyr/net/offloaded_netdev.h>

#include "modem_receiver.h"

#define DT_DRV_COMPAT st_87m01

#define MDM_UART_NODE DT_INST_BUS(0)
#define MDM_UART_DEV  DEVICE_DT_GET(MDM_UART_NODE)

#define MDM_MAX_DATA_LENGTH 1024
#define MDM_RECV_MAX_BUF    30
#define MDM_RECV_BUF_SIZE   128

#define MDM_MAX_SOCKETS 6

/*
 * Default length of modem data.
 */
#define MDM_MANUFACTURER_LENGTH 12
#define MDM_MODEL_LENGTH        16
#define MDM_REVISION_LENGTH     64
#define MDM_IMEI_LENGTH         16
#define MDM_IMSI_LENGTH         16
#define MDM_ICCID_LENGTH        32


/* driver data */
struct modem_data {
	/* modem data */
	char mdm_manufacturer[MDM_MANUFACTURER_LENGTH];
	char mdm_model[MDM_MODEL_LENGTH];
	char mdm_revision[MDM_REVISION_LENGTH];
	char mdm_imei[MDM_IMEI_LENGTH];
	char mdm_imsi[MDM_IMSI_LENGTH];
	int mdm_rssi;
};

static struct modem_data mdata;
static struct mdm_receiver_context mctx;

static uint8_t mdm_recv_buf[MDM_MAX_DATA_LENGTH];

static void modem_reset(void);
static void offload_iface_init(struct net_if *iface);

static struct offloaded_if_api api_funcs = {
	.iface_api.init = offload_iface_init,
};

• drivers/modem/CMakeLists.txt

if (CONFIG_MODEM_ST87M01)
	zephyr_library_sources(st87m01.c)
endif()

• dts/bindings/modem/st,87m01.yaml

description: ST87M01 NBIoT modem

compatible: "st,87m01"

include: uart-device.yaml

properties:
  mdm-reset-gpios:
    type: phandle-array
    required: true

  mdm-dcdc-gpios:
    type: phandle-array

Test app

• prj.conf

CONFIG_NETWORKING=y

CONFIG_SHELL=y
CONFIG_SHELL_WILDCARD=n

CONFIG_MODEM=y
CONFIG_MODEM_ST87M01=y
# CONFIG_MODEM_AT_SHELL=y

• boards/nucleo_h503rb.overlay

/ {
        aliases {
                modem = &st_87m01;
        };
};

&arduino_serial {
	current-speed = <115200>;
	status = "okay";
};

• src/main.c

#include <zephyr/kernel.h>
#include <zephyr/shell/shell.h>
#include <zephyr/device.h>

const struct device *modem = DEVICE_DT_GET(DT_ALIAS(modem));

int main(void)
{
	return 0;
}

Build logs

-- west build: making build dir /home/nicoth/projects/ST-project-workspace/applications/at-shell-app/build pristine
-- west build: generating a build system
Loading Zephyr default modules (Zephyr base).
-- Application: /home/nicoth/projects/ST-project-workspace/applications/at-shell-app
-- CMake version: 3.31.6
-- Found Python3: /home/nicoth/projects/ST-project-workspace/.venv/bin/python (found suitable version "3.13.2", minimum required is "3.10") found components: Interpreter
-- Cache files will be written to: /home/nicoth/.cache/zephyr
-- Zephyr version: 4.1.0-rc2 (/home/nicoth/projects/ST-project-workspace/zephyr)
-- Found west (found suitable version "1.3.0", minimum required is "0.14.0")
-- Board: nucleo_h503rb, qualifiers: stm32h503xx
-- Shield(s): st87m01
-- ZEPHYR_TOOLCHAIN_VARIANT not set, trying to locate Zephyr SDK
-- Found host-tools: zephyr 0.17.0 (/home/nicoth/zephyr-sdk-0.17.0)
-- Found toolchain: zephyr 0.17.0 (/home/nicoth/zephyr-sdk-0.17.0)
-- Found Dtc: /home/nicoth/zephyr-sdk-0.17.0/sysroots/x86_64-pokysdk-linux/usr/bin/dtc (found suitable version "1.6.0", minimum required is "1.4.6")
-- Found BOARD.dts: /home/nicoth/projects/ST-project-workspace/zephyr/boards/st/nucleo_h503rb/nucleo_h503rb.dts
-- Found devicetree overlay: /home/nicoth/projects/ST-project-workspace/zephyr/boards/shields/st87m01/st87m01.overlay
-- Found devicetree overlay: /home/nicoth/projects/ST-project-workspace/applications/at-shell-app/boards/nucleo_h503rb.overlay
-- Generated zephyr.dts: /home/nicoth/projects/ST-project-workspace/applications/at-shell-app/build/zephyr/zephyr.dts
-- Generated pickled edt: /home/nicoth/projects/ST-project-workspace/applications/at-shell-app/build/zephyr/edt.pickle
-- Generated devicetree_generated.h: /home/nicoth/projects/ST-project-workspace/applications/at-shell-app/build/zephyr/include/generated/zephyr/devicetree_generated.h
-- Including generated dts.cmake file: /home/nicoth/projects/ST-project-workspace/applications/at-shell-app/build/zephyr/dts.cmake
Parsing /home/nicoth/projects/ST-project-workspace/zephyr/Kconfig
Loaded configuration '/home/nicoth/projects/ST-project-workspace/zephyr/boards/st/nucleo_h503rb/nucleo_h503rb_defconfig'
Merged configuration '/home/nicoth/projects/ST-project-workspace/applications/at-shell-app/prj.conf'
Configuration saved to '/home/nicoth/projects/ST-project-workspace/applications/at-shell-app/build/zephyr/.config'
Kconfig header saved to '/home/nicoth/projects/ST-project-workspace/applications/at-shell-app/build/zephyr/include/generated/zephyr/autoconf.h'
-- Found GnuLd: /home/nicoth/zephyr-sdk-0.17.0/arm-zephyr-eabi/arm-zephyr-eabi/bin/ld.bfd (found version "2.38")
-- The C compiler identification is GNU 12.2.0
-- The CXX compiler identification is GNU 12.2.0
-- The ASM compiler identification is GNU
-- Found assembler: /home/nicoth/zephyr-sdk-0.17.0/arm-zephyr-eabi/bin/arm-zephyr-eabi-gcc
-- Using ccache: /usr/bin/ccache
-- Configuring done (7.7s)
-- Generating done (0.2s)
-- Build files have been written to: /home/nicoth/projects/ST-project-workspace/applications/at-shell-app/build
-- west build: building application
[1/201] Preparing syscall dependency handling

[2/201] Generating include/generated/zephyr/version.h
-- Zephyr version: 4.1.0-rc2 (/home/nicoth/projects/ST-project-workspace/zephyr), build: 1d169fb16731
[196/201] Linking C executable zephyr/zephyr_pre0.elf
FAILED: zephyr/zephyr_pre0.elf zephyr/zephyr_pre0.map /home/nicoth/projects/ST-project-workspace/applications/at-shell-app/build/zephyr/zephyr_pre0.map
: && ccache /home/nicoth/zephyr-sdk-0.17.0/arm-zephyr-eabi/bin/arm-zephyr-eabi-gcc  -gdwarf-4 zephyr/CMakeFiles/zephyr_pre0.dir/misc/empty_file.c.obj -o zephyr/zephyr_pre0.elf  zephyr/CMakeFiles/offsets.dir/./arch/arm/core/offsets/offsets.c.obj  -T  zephyr/linker_zephyr_pre0.cmd  -Wl,-Map=/home/nicoth/projects/ST-project-workspace/applications/at-shell-app/build/zephyr/zephyr_pre0.map  -Wl,--whole-archive  app/libapp.a  zephyr/libzephyr.a  zephyr/arch/common/libarch__common.a  zephyr/arch/arch/arm/core/libarch__arm__core.a  zephyr/arch/arch/arm/core/cortex_m/libarch__arm__core__cortex_m.a  zephyr/arch/arch/arm/core/cortex_m/cmse/libarch__arm__core__cortex_m__cmse.a  zephyr/arch/arch/arm/core/mpu/libarch__arm__core__mpu.a  zephyr/lib/libc/picolibc/liblib__libc__picolibc.a  zephyr/lib/libc/common/liblib__libc__common.a  zephyr/lib/posix/options/liblib__posix__options.a  zephyr/lib/net_buf/liblib__net_buf.a  zephyr/subsys/random/libsubsys__random.a  zephyr/subsys/net/l2/offloaded_netdev/libsubsys__net__l2__offloaded_netdev.a  zephyr/subsys/net/ip/libsubsys__net__ip.a  zephyr/drivers/interrupt_controller/libdrivers__interrupt_controller.a  zephyr/drivers/clock_control/libdrivers__clock_control.a  zephyr/drivers/console/libdrivers__console.a  zephyr/drivers/entropy/libdrivers__entropy.a  zephyr/drivers/gpio/libdrivers__gpio.a  zephyr/drivers/modem/libdrivers__modem.a  zephyr/drivers/pinctrl/libdrivers__pinctrl.a  zephyr/drivers/reset/libdrivers__reset.a  zephyr/drivers/serial/libdrivers__serial.a  zephyr/drivers/timer/libdrivers__timer.a  modules/hal_stm32/stm32cube/lib..__modules__hal__stm32__stm32cube.a  -Wl,--no-whole-archive  zephyr/kernel/libkernel.a  -L/home/nicoth/projects/ST-project-workspace/applications/at-shell-app/build/zephyr  zephyr/arch/common/libisr_tables.a  -mcpu=cortex-m33  -mthumb  -mabi=aapcs  -mfp16-format=ieee  -mtp=soft  -fuse-ld=bfd  -Wl,--gc-sections  -Wl,--build-id=none  -Wl,--sort-common=descending  -Wl,--sort-section=alignment  -Wl,-u,_OffsetAbsSyms  -Wl,-u,_ConfigAbsSyms  -nostdlib  -static  -Wl,-X  -Wl,-N  -Wl,--orphan-handling=warn  -Wl,-no-pie  -specs=picolibc.specs  -DPICOLIBC_LONG_LONG_PRINTF_SCANF -L"/home/nicoth/zephyr-sdk-0.17.0/arm-zephyr-eabi/bin/../lib/gcc/arm-zephyr-eabi/12.2.0/thumb/v8-m.main/nofp" -lc -lgcc && cd /home/nicoth/projects/ST-project-workspace/applications/at-shell-app/build/zephyr && /usr/bin/cmake -E true
/home/nicoth/zephyr-sdk-0.17.0/arm-zephyr-eabi/bin/../lib/gcc/arm-zephyr-eabi/12.2.0/../../../../arm-zephyr-eabi/bin/ld.bfd: Undefined initialization levels used.
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.
FATAL ERROR: command exited with status 1: /usr/bin/cmake --build /home/nicoth/projects/ST-project-workspace/applications/at-shell-app/build

[github-actions[bot]]

Hi @Captainfl4me! We appreciate you submitting your first issue for our open-source project. 🌟

Even though I'm a bot, I can assure you that the whole community is genuinely grateful for your time and effort. 🤖💙

[pdgendt]

Kconfig options in C have the CONFIG_ prefix, so:

/* Register device with the networking stack. */
NET_DEVICE_DT_INST_OFFLOAD_DEFINE(0, modem_init, NULL, &mdata, NULL, CONFIG_MODEM_ST87M01_INIT_PRIORITY,
				  &api_funcs, MDM_MAX_DATA_LENGTH);

[Captainfl4me]

Oh thank you so much! I already knew that, but despite several rereads I hadn't noticed the mistake.

[pdgendt]

Oh thank you so much! I already knew that, but despite several rereads I hadn't noticed the mistake.

If this resolves your issue, please close it, or I would convert it to a discussion instead.

[Captainfl4me]

Maybe it would be better to convert it to a discussion as I may have other questions regarding this implementation. This would avoid creating multiple issues in the future.

[Captainfl4me]

Hello again,

I manage to write the necessary offloading point to run a simple application opening socket on an UDP socket echo server, send data to it using the sendto function, read the data back with the recv function and finally closing the socket. So I basically implement the 4 offloading points get, sendto, recv and put and register through net_offload struct.

Now, I was trying to continue testing the implementation using this time the NET_SHELL through net udp bind command. This call the get offload point but never reach the bind offload point. Instead, during the ipv4 addr setup, I get a Binding to UDP port failed (-2). I trace back the error to the net_context_bind function and more precisely net_if_ipv4_addr_lookup or net_if_ipv4_maddr_lookup inside.

Am I using the command right net udp bind x.x.x.x 5000? Or is it a configuration problem? Or even something else?

prj.conf

CONFIG_NETWORKING=y
CONFIG_NET_NATIVE=y
CONFIG_NET_IPV4=y
CONFIG_NET_UDP=y
CONFIG_NET_SHELL=y

CONFIG_SHELL=y
CONFIG_SHELL_WILDCARD=n

CONFIG_MODEM=y
CONFIG_MODEM_ST87M01=y
CONFIG_MODEM_ST87M01_MAX_RX_DATA_LENGTH=256
CONFIG_MODEM_ST87M01_MAX_TX_DATA_LENGTH=128
CONFIG_MODEM_ST87M01_RX_STACK_SIZE=700