MCP7940 device tree implementation

[ljch]

Hi I am receiving the error "Linking C executable zephyr\zephyr_pre0.elf FAILED:" which I have found is linked to the mcp7940 device tree node through the error code " undefined reference to `__device_dts_ord_57'" in the device_generated.h file. I want to include in the device tree the interrupt that the mcp7940  on gpio 0 21 of the NRF52805 but I'm not sure if this is best practice or not. How do I solve this error and include the gpio interrupt in the device tree?

Here is the device tree node for the MCP7940n and the corresponding device tree binding.

Device Tree node

&i2c0 {
    status = "okay";
    pinctrl-0 =<&i2c0_default>;
    pinctrl-1 =<&i2c0_sleep>;
    pinctrl-names = "default","sleep";
    clock-frequency = <100000>;
    
    mcp7940n: mcp7940n@6f {
        compatible = "microchip,mcp7940n";
        reg = <0x6f>;
        label = "MCP7940N_RTC";
        //int-gpios = <&gpio0 21 GPIO_ACTIVE_LOW>;  // Use actual GPIO pin where interrupt is connected
    };
};

.yaml binding

#
# Copyright (c) 2021 Laird Connectivity
# Copyright (c) 2023 Nordic Semiconductor ASA
#
# SPDX-License-Identifier: Apache-2.0
#

description: Microchip MCP7940N I2C RTC with battery-backed SRAM

compatible: "microchip,mcp7940n"

include: i2c-device.yaml

properties:
  reg:
    type: array
    description: |
      The I2C address of the device 0x6F
      

[ljch]

I am using the nrf connect SDK 2.6.1 and here is my proj.conf file

CONFIG_RTT_CONSOLE=y
CONFIG_I2C=y
CONFIG_LOG=y

and the custom board defconfig file

 Copyright (c) 2024 Nordic Semiconductor ASA
# SPDX-License-Identifier: Apache-2.0

CONFIG_SOC_SERIES_NRF52X=y
CONFIG_SOC_NRF52805_CAAA=y
CONFIG_BOARD_CESSADK_NRF52805=y

# Enable MPU
CONFIG_ARM_MPU=y

# Enable hardware stack protection
CONFIG_HW_STACK_PROTECTION=y

# enable GPIO
CONFIG_GPIO=y

# enable console
CONFIG_CONSOLE=y

# enable RTT console
CONFIG_USE_SEGGER_RTT=y

# additional board options
CONFIG_GPIO_AS_PINRESET=n

CONFIG_PINCTRL=y

# enable internal oscillator
CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC=y
CONFIG_CLOCK_CONTROL_NRF_K32SRC_500PPM=y
CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC_CALIBRATION=y
CONFIG_CLOCK_CONTROL_NRF_CALIBRATION_LF_ALWAYS_ON=y

here is the main.c code

/*
 * Copyright (c) 2016 Intel Corporation
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include <zephyr/kernel.h>
#include <zephyr/drivers/gpio.h>
#include <zephyr/logging/log.h>
#include <zephyr/drivers/i2c.h>

/* 1000 msec = 1 sec */
#define SLEEP_TIME_MS   1000

/* The devicetree node identifier for the "led0" alias. */
#define LED0_NODE DT_ALIAS(led0)
#define RTC_NODE DT_NODELABEL(mcp7940n)

#define MCP7940_ADDR 0x6F
#define RTCSEC_ADDR 0x00
#define RTCMIN_ADDR 0x01
#define RTCSHOUR_ADDR 0x02
#define RTCWKD_ADDR 0x03
/*
 * A build error on this line means your board is unsupported.
 * See the sample documentation for information on how to fix this.
 */
LOG_MODULE_REGISTER(maindev, LOG_LEVEL_DBG);
static const struct gpio_dt_spec led = GPIO_DT_SPEC_GET(LED0_NODE, gpios);



int main(void)
{
	const struct device *rtc_dev; 
	rtc_dev = DEVICE_DT_GET(RTC_NODE);
	uint8_t write_msg = 0x00; 
	uint8_t read_sec_msg = 255; 
	uint8_t read_wkd_msg = 0;
	
	int ret;
    // Get the I2C device
	

    if (!device_is_ready(rtc_dev)) {
        LOG_ERR("I2C device not ready");
        return 0;
    }
	if (!gpio_is_ready_dt(&led)) {
		LOG_ERR("LED not ready");
		return 0;
	}

	//load the rtc sec register with 0 while the osc is disabled
	ret = i2c_reg_write_byte(rtc_dev, MCP7940_ADDR,RTCSEC_ADDR, 0);
	
	if(ret){
		LOG_ERR("write to osc start bit failed error = %d",ret);
	}

	write_msg |= 0x80; //SET THE START OSCILLATOR BIT 

	//write to the start bit of the oscillator
	ret = i2c_reg_write_byte(rtc_dev, MCP7940_ADDR,RTCSEC_ADDR,write_msg);
	
	if(ret){
		LOG_ERR("write to rtc second register failed error = %d",ret);
	}

	//wait three seconds
	k_msleep(1000);
	k_msleep(1000);
	k_msleep(1000);

	//read the sec register after waiting 3 seconds
	ret = i2c_reg_read_byte(rtc_dev,MCP7940_ADDR, RTCSEC_ADDR,&read_sec_msg);

	if(ret){
		LOG_ERR("read to rtc second register failed error = %d",ret);
	}


	//read the rtc second address to see if one second has passed
	ret = i2c_reg_read_byte(rtc_dev,MCP7940_ADDR, RTCWKD_ADDR,&read_wkd_msg);
	
	
	if(ret){
		LOG_ERR("read to rtc second register failed error = %d",ret);
	}
	
	LOG_INF("here is the read message: 0x%02X", read_sec_msg);
	LOG_INF("here is the wkd register contents: 0x%02X", read_wkd_msg);
	

	ret = gpio_pin_configure_dt(&led, GPIO_OUTPUT_ACTIVE);
	if (ret < 0) {
		return 0;
	}

	while (1) {
		ret = gpio_pin_toggle_dt(&led);
		if (ret < 0) {
			return 0;
		}
		k_msleep(SLEEP_TIME_MS);
	}
	return 0;
}

[Simonr]

Hi

So, the device_dts_ord_xx error in itself doesn't tell us much other than that the device tree structure (dts) is missing something. Please check out the file in build\zephyr\include\generated\devicetree_generated.h and check what the number 57 corresponds to. You can check out the DevAcademy lesson on troubleshooting the devicetree here: https://academy.nordicsemi.com/courses/nrf-connect-sdk-intermediate/lessons/lesson-2-debugging/topic/troubleshooting-the-devicetree/ 

Best regards,

Simon

[ljch]

Hi Simon, I did check line 57 and it said it corresponded to the MCP7940 RTC. I ended up scrapping the custom driver and just used the generic i2c driver api.