[SOLVED] Make a bit to zero without using "~" and affecting other bits in a register - ARM Compiler 6 (ARMClang compiler)

[Raguvaran]

Hi, I am in basic level of embedded C. Using Keil for STM32 programming. For bit set and reset i use "|=" and "&=~". Below is a code

GPIOA->ODR |= (1<<5); // PA5 = 1
GPIOA->ODR &=~ (1<<5); // PA5 = 0

While using ARM Compiler Version 5 there is no issue.
In ARM Compiler 6 (ARMClang compiler), I am getting a warning while using "~" that

main.c(28): warning: implicit conversion changes signedness: 'int' to 'unsigned int' [-Wsign-conversion]
GPIOA->ODR &=~ (1<<5); // PA5 = 0
~~^~~~~~~~

By reading a document "Migrate ARM Compiler 5 to ARM Compiler 6", I understood the Bit-field Signedness in ARM Compiler 5 is default unsigned and in ARM Compiler 6 is default signed

My Question is,
1) Now how i have make a bit to zero without using "~" and affecting other bits in a register?
2) Is it ok to use "|=" to make a bit to 1?
3) Is any other effective way to make a bit to zero or one without affecting other bits in a register?

Kindly apology me if my question is very basic,
Thank you in advance

 

[KlausST]

Hi,

A warning is no error, thus I assume everything is working as expected.

*****
I'm no expert either....so what I'd try is
* typecasting: set "(unsigned int)" before "(1<<5)"
* or use HAL functions
* or use BRR instruction

Just did an internet search "keil bit clear arm". (Didn't you do something similar on your own before?)
There are a lot of interesting documents.
There seems to be a BIC function and a CLEAR_BIT function...

You may also try other internet search like: "keil arm clear port pins"

Klaus

 

[danadakk]

Why not a simple AND to clear the bit ? If compiler still complains then do a cast
first, if your signedness is known before the cast....

Not a C expert, but thats what I would try.

Regards, Dana.

 

[Raguvaran]

Hi,

A warning is no error, thus I assume everything is working as expected.

*****
I'm no expert either....so what I'd try is
* typecasting: set "(unsigned int)" before "(1<<5)"
* or use HAL functions
* or use BRR instruction

Just did an internet search "keil bit clear arm". (Didn't you do something similar on your own before?)
There are a lot of interesting documents.
There seems to be a BIC function and a CLEAR_BIT function...

You may also try other internet search like: "keil arm clear port pins"

Klaus

Thank you Klaus

This code shoes no error
{
GPIOA->ODR |= (1<<5); // PA5 = 1
delayMs(500);
GPIOA->ODR &=~ (unsigned int)(1<<5); // PA5 = 0
delayMs(500);
}

and also tried SET_BIT and CLEAR_BIT functions as you mentioned.
{
SET_BIT(GPIOA->ODR, GPIO_ODR_OD5); // PA5 = 1
delayMs(500);
CLEAR_BIT(GPIOA->ODR, GPIO_ODR_OD5); // PA5 = 0
delayMs(500);
}

As reading further I understood that using BSRR and BRR is efficient compared to using ODR. Because accessing ODR takes more cycles.
Thank you for your guidance.

Hope this help others.

--- Updated Jun 6, 2021 ---

Why not a simple AND to clear the bit ? If compiler still complains then do a cast
first, if your signedness is known before the cast....

Not a C expert, but thats what I would try.

Regards, Dana.

Thank you for your reply.

direct AND may affect other bits in a register.

Maybe if i am wrong, kindly correct me..

 

[BradtheRad]

To set a bit to zero, execute AND with a number consisting of 1's in all the other bit positions.

Example, to clear the rightmost bit of 8 bits, execute AND and 254. It leaves the leftmost 7 bits unchanged.