How to parse and read JSON file correctly?

[Aduka_27]

Hi guys,

I am using the nRF52832 board and I want to parse and read my JSON file. I don't have too much experience working with cJSON and here you will find my simple code where I try to understand how to define things properly. I will appreciate a lot if you can help me with some advice or better if you can suggest me where I made errors.

Best regards,

Adnan.

/*
 * Copyright (c) 2012-2014 Wind River Systems, Inc.
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include <zephyr.h>
#include <sys/printk.h>
#include <string.h>
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <float.h>
#include <limits.h>
#include <ctype.h>
#include "cJSON.h"


char *create_hello(void) {
	
	char *string;
	
	cJSON *hello = cJSON_CreateObject();
	
	cJSON *functionName = cJSON_CreateString("hello_world");
	cJSON_AddItemToObject(hello, "functionName", functionName);
	
	string = cJSON_Print(hello);
	
	cJSON_Delete(hello);
	return string;
	
	}

void hello_world (void) {
	
	printk("Hello World! %s\n", CONFIG_BOARD);
	}


void main(void)
{
	const char *hello = "{\"functionName\": \"hello_world\"}";
	cJSON *hello_json = cJSON_Parse(hello);
	cJSON *functionName = cJSON_GetObjectItemCaseSensitive(hello_json, "functionName");
	
	while(true){
		
		if (functionName == "hello_world") {
			hello_world();
			k_sleep(K_SECONDS(1));
			}		
			
		}
}

[Carl Richard]

Hello, Aduka!

Thank you for reaching out. First of all, have you defined the correct prj.conf for your application? Mine looks like this for the hello_world sample:

# nothing here
CONFIG_CJSON_LIB=y

# newlibc
CONFIG_NEWLIB_LIBC=y

Secondly, your code is mostly correct, but you have done an illegal comparison in your while loop. Look at my main below, where the error is corrected:

void main(void)
{
	const char *hello = "{\"functionName\": \"hello_world\"}";
	cJSON *hello_json = cJSON_Parse(hello);
	char* functionName = cJSON_Print(cJSON_GetObjectItemCaseSensitive(hello_json, "functionName"));
	
	while(true){
		
		if (strcmp(functionName, "hello_world")) {
			hello_world();
			k_sleep(K_SECONDS(1));
			}		
			
		}
}

In the code above I have changed line 45 so that cJSON_Print is used to write the content to a string. Then I have changed 49 to use strcmp, for comparing the strings. The line numbers I reference are from your original code. 

Hope this helps you on your way, and please reach out if you wonder about anything else. 

Best regards,
Carl Richard

[Aduka_27]

Hi Carl,

Thanks a lot for this help and suggestions! I tried this code with these corrections, but again I am not able to compile it on my board. Now the problem occurs in my proj.conf file I think.

This is the error:

error: Aborting due to Kconfig warnings

CMake Error at /home/adnan/zephyrproject/zephyr/cmake/kconfig.cmake:217 (message):
command failed with return code: 1
Call Stack (most recent call first):
/home/adnan/zephyrproject/zephyr/cmake/app/boilerplate.cmake:510 (include)
/home/adnan/zephyrproject/zephyr/share/zephyr-package/cmake/ZephyrConfig.cmake:24 (include)
/home/adnan/zephyrproject/zephyr/share/zephyr-package/cmake/ZephyrConfig.cmake:40 (include_boilerplate)
CMakeLists.txt:5 (find_package)

-- Configuring incomplete, errors occurred!
See also "/home/adnan/zephyrproject/zephyr/build/CMakeFiles/CMakeOutput.log".
See also "/home/adnan/zephyrproject/zephyr/build/CMakeFiles/CMakeError.log".
FAILED: build.ninja
/usr/bin/cmake --regenerate-during-build -S/home/adnan/zephyrproject/zephyr/samples/hello_world_cjson -B/home/adnan/zephyrproject/zephyr/build
ninja: error: rebuilding 'build.ninja': subcommand failed
FATAL ERROR: command exited with status 1: /usr/bin/cmake --build /home/adnan/zephyrproject/zephyr/build

Can you maybe figure out what could be a potential problem now? And also, I forgot to tell that I use Zephyr if that is important for this problem. Also, my last question is related to Makefile and prj.conf files...where I can find the proper configuration for different samples. For sure, I will need to use cJSON together with my BLE example.

Thanks in advance and best regards,

Adnan.

[Carl Richard]

I see that I have to clear some things up. The nRF Connect SDK (NCS) is in fact Nordic-specific code supplementing Zephyr. We maintain our own Zephyr fork, so that all samples and code is available for use with our products. You can read more about how it's tied together here.

With that said we recommend using NCS with our products as we can't ensure proper function or support when using Zephyr standalone. Hence, you should follow the instructions for setting up NCS, located here. We have tried to make the setup and installation as straight-forward as possible, but we have instructions for manual installation as well.

This also explains why your code doesn't compile properly, as cJSON is not a part of Zephyr RTOS standalone (they use their own implementation).

You're no bother! I understand that this is confusing. Please ask if anything else is unclear!

PS: for standalone Zephyr RTOS support your should look at their official channels.

Best regards,
Carl Richard

[Aduka_27]

Hi Carl,

Thanks for this super clear explanation! I have already registered to their official channels and asked the same question, but they also sent me some examples related to nRF Connect. Is it possible to mix these examples from Zephyr and nRF Connect SDK documentation? For example, can I put everything in one folder and use all features for both of them if you understand me what I mean?

Best regards,

Adnan.

[Carl Richard]

Hello again, Adnan!

My pleasure. And yes, as the nRF Connect SDK is based on Zephyr it should be no problems to mix them. However, we maintain our own fork of the Zephyr RTOS repo, which usually are a bit behind the main repository. To ensure that your Zephyr version is compatible with the nRF Connect SDK I recommend installing it as linked in my previous comment. This will also give you access to all Zephyr's features.

Best regards,
Carl Richard

[Aduka_27]

Hi Carl,

How to add all these things inside my zephyrproject folder where I installed Zephyr standalone with all the necessary toolchain and tools? Or I need to uninstall my Zephyr and start from the scratch again. This is quite confusing for me?

Best regards,

Adnan.

[Carl Richard]

Hi! 

Sorry, did not mean to confuse youI recommend that you install nRF Connect SDK (which includes Zephyr) from scratch, as described in this guide. It could also be that your current Zephyr installation will interfere NCS, so if it's not needed I recommend uninstalling it. 

Best regards,
Carl Richard

[Aduka_27]

Hi Carl,

But I need this because of same samples that I use as a base for my app. For example, in your documentation I cannot find this sample for battery voltage reading or this one with temperature sensing and sending data via BLE. Because all of these things, I asked you if it is possible to use both of them in same directory?

Best regards,

Adnan.

[Carl Richard]

Hi, Adnan!

Could you provide a link to the samples you are referring to? I'll have a look. If I understand you correctly, then yes, the samples can be combined and used in one directory.

To be clear: The full Zephyr RTOS is available as a part of NCS.

Best regards,
Carl Richard

[Aduka_27]

Hi Carl,

Yes of course I will provide you the samples that I use. To be clear enough, I use this sample where I can get the values for temperature and battery level (in percentage) and send them to my central node on which for now I am only able to read temperature value. Then, I put this part related to voltage reading just because I wanted to convert these percentages into mV (integer). Now, I got some values in percentage that I don't know how to make the relation between them and mV. Still, my central node is not able to read the battery level that I want to sent him from my peripheral one, and I don't know how to implement that service. Do you suggest me to uninstall my Zephyr standalone and install the nRF Connect SDK with all samples that were already included in Zephyr standalone documentation?

These are links of examples that I use for now:

https://github.com/nrfconnect/sdk-zephyr/tree/master/samples/boards/nrf/battery - for voltage reading

https://github.com/nrfconnect/sdk-zephyr/tree/master/samples/bluetooth/peripheral_ht - for temperature and battery level reading / peripheral node

https://github.com/nrfconnect/sdk-zephyr/tree/master/samples/bluetooth/central_ht - central node

[Carl Richard]

I see. Thanks for providing the links. 

First: don't know how much you have edited the samples, but from what I can see the peripheral_ht "simulates" the battery level by setting it to 100. Furthermore the Battery Service(BAS) operates with percentages. To calculate these you must know the maximum capacity of your battery, and measure the voltage as you describe.

Secondly: Yes, I do suggest this. You will get access to the same samples, but in an development environment maintained and supported by us.

Best regards,
Carl Richard

[Aduka_27]

Hi Carl,

I did not uninstall my Zephyr standalone, but I am trying to add sdk-nrf v1.3.2 release to my existing zephyrproject repository. Is that possible or I make the mistake doing this procedure in that way? Also, trying this I got some error like: FATAL ERROR: already initialized in /home/adnan/zephyrproject, aborting. I found that I can resolve this issue unsetting the ZEPHYR_BASE environmental variable. Also, do you maybe know which is the procedure of uninstalling to all existing zephyrproject repository in case that I cannot finish my job like I explained above? And, my last question where can I unset this variable in my documentation?

Best regards,

Adnan.