nrf9160 - sscanf() - Length field (%hhi, %hhu)

RE: nrf9160 - sscanf() - Length field (%hhi, %hhu)

Håkon Alseth — Wed, 17 Mar 2021 08:21:00 GMT

Hi Rene,

Thank you, this clearly shows the issue.

It seems that newlib nano does not support 8 bit IO types:

https://bugs.launchpad.net/bugs/1598122

At my end, the compiler must have placed variables in 4 byte alignment.

Kind regards,

Håkon

RE: nrf9160 - sscanf() - Length field (%hhi, %hhu)

ReneDelgado — Tue, 16 Mar 2021 20:53:40 GMT

Hi,

Could you tell me where can I see my version of arm-none-eabi-gcc?

Your example runs well , but that example Is not affected by the byte corruptions for that I added an example with a Union to describe better my problem. here is the output of the example. my_array[1] was corrupted

******************************** Original array state
my_array[0]: 1
my_array[1]: 2
my_array[2]: 3
my_array[3]: 4
******************************** Updating my_var
my_var: 7
******************************** Array after the data update, my_array[1] was corrupted
my_array[0]: 7
my_array[1]: 0
my_array[2]: 3
my_array[3]: 4

Thanks you

RE: nrf9160 - sscanf() - Length field (%hhi, %hhu)

Håkon Alseth — Mon, 15 Mar 2021 07:39:51 GMT

Hi René,

[quote user="ReneDelgado"]What should we do to use that the "%hhu" specifier correctly?[/quote]

As mentioned, the newlib standard functions are provided with the compiler itself, so there might be a bug there or in the handling.

Which version of arm-none-eabi-gcc are you using?

What is the output in your case?

Did you try the code that I posted, and how did it behave?

Kind regards,

Håkon

RE: nrf9160 - sscanf() - Length field (%hhi, %hhu)

ReneDelgado — Sat, 13 Mar 2021 22:32:00 GMT

Hello, thanks for your response,

Here is an example that describes better the problem, apparently sscanf () is interpreting the specifier "%hhu" as "%hu". The above causes the next byte to be written incorrectly.

const int8_t str_dummy [8] = "7\r\n";
union dummy_union_t 
{
    uint8_t my_var;
	uint8_t my_array[4];
};
    

union dummy_union_t my_union = 
{
    .my_array[0] = 1,
	.my_array[1] = 2,
	.my_array[2] = 3,
	.my_array[3] = 4,
}; 

printk("******************************** Original array state\n");    
printk("my_array[0]: %hhu\n", my_union.my_array[0]);
printk("my_array[1]: %hhu\n", my_union.my_array[1]);
printk("my_array[2]: %hhu\n", my_union.my_array[2]);
printk("my_array[3]: %hhu\n", my_union.my_array[3]);

printk("******************************** Updating my_var\n");
sscanf(str_dummy, "%hhu", &my_union.my_var);
printk("my_var: %hhu\n", my_union.my_var);
	
printk("******************************** Array after the data update, my_array[1] was corrupted\n");
printk("my_array[0]: %hhu\n", my_union.my_array[0]);
printk("my_array[1]: %hhu\n", my_union.my_array[1]);
printk("my_array[2]: %hhu\n", my_union.my_array[2]);
printk("my_array[3]: %hhu\n", my_union.my_array[3]);

What should we do to use that the "%hhu" specifier correctly?

Thanks a lot,

René D.

RE: nrf9160 - sscanf() - Length field (%hhi, %hhu)

Håkon Alseth — Mon, 08 Mar 2021 09:20:03 GMT

Hi,

sscanf() is provided by newlib, which again comes with your local compiler (arm-none-eabi).

Could you check if the code snippet shown here runs as expected on your end?

https://www.tutorialspoint.com/c_standard_library/c_function_sscanf.htm

I also added this small snippet to the above code, and that ran that:

		char var[100];
		char i;
		strcpy(var, "Something Something: 123");
		sscanf(var, "Something Something: %hhu", &i);
		printk("i: %u\n", i);
		
		int day, year;
		char weekday[20], month[20], dtm[100];
		strcpy( dtm, "Saturday March 25 1989" );
		sscanf( dtm, "%s %s %d  %d", weekday, month, &day, &year );
		printk("%s %d, %d = %s\n", month, day, year, weekday );
		
		k_msleep(1000);

Which prints:

i: 123
March 25, 1989 = Saturday

I added the above code in hello_world, with these additional configs:

CONFIG_NEWLIB_LIBC=y
CONFIG_NEWLIB_LIBC_FLOAT_PRINTF=y
CONFIG_NEWLIB_LIBC_FLOAT_SCANF=y
CONFIG_MAIN_STACK_SIZE=4096

Kind regards,

Håkon