Associate III

Question

simple stm32 c question ?

Forum|Forum|13 years ago
May 9, 2013
9 replies
2471 views

Posted on May 10, 2013 at 00:34

what is this 1ul and 2ul and 3ul

examble

RCC->AHB1ENR |= ((1UL << 0) ); /* Enable GPIOA clock *

GPIOA->MODER &= ~((3UL << 2*0) ); /* PA.0 is input */

what is the new value for RCC->AHB1ENR and GPIOA->MODER

#c-basics #off-topic

This topic has been closed for replies.

Tesla DeLorean

Guru

Posted on May 10, 2013 at 00:40

UL means the number is handled as an Unsigned Long,

RCC->AHB1ENR |= 0x00000001;

GPIOA->MODER &= 0xFFFFFFFC; // mask off low two bits ie ~0x00000003

The final state will depend on the initial state of the registers.

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jbl_rawAuthor

Associate III

Posted on May 10, 2013 at 15:28

RCC->AHB1ENR |= 0x00000001;

GPIOA->MODER &= 0xFFFFFFFC; // mask off low two bits ie ~0x00000003

thank you very much

but how you convert this (3UL << 2*0) and this (1UL << 0) to number !

Tesla DeLorean

Guru

Posted on May 10, 2013 at 15:53

but how you convert this (3UL << 2*0) and this (1UL << 0) to number !

I'm not sure I understand the question. The compiler parses suffixes which imply type information which it uses to do the computation, which can be different from the type it is later stored in, or other variables used in the computation. (Like using L to specify a long, on a compiler that would normally hold the value in 16-bit, or F to specify a float rather than a double)

(3UL << 2*0)

3 << 0

3

~3 is equivalent to 3 ^ 0xFFFFFFFF, ie the inverse or logical NOT

A quick Google

http://www.parashift.com/c++-faq/numeric-literal-suffixes.html

http://hackipedia.org/Platform/3D0/html%2c%203DO%20SDK%20Documentation/Type%20A/tktfldr/arrfldr/1arrg.html

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Andrew Neil

Super User

Posted on May 11, 2013 at 00:25

Note that none of this has anything to do with the STM32 - it is all just normal, standard 'C' syntax.

Time to dust-off that 'C' textbook...

http://blog.antronics.co.uk/2010/12/12/things-you-shouldve-learned-in-c-class-0-introduction/

A complex system that works is invariably found to have evolved from a simple system that worked.A complex system designed from scratch never works and cannot be patched up to make it work.

Tesla DeLorean

Guru

Posted on May 11, 2013 at 14:33

Note that none of this has anything to do with the STM32

The code is an example out there for the chip, it's not an unreasonable question, we want to cultivate this as a safe place to ask question, or seek clarifications.

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Andrew Neil

Super User

Posted on May 12, 2013 at 19:00

Yes; but it's important to understand that this is just standard'C' syntax - not something that's in any way specific to the STM32 itself.

A complex system that works is invariably found to have evolved from a simple system that worked.A complex system designed from scratch never works and cannot be patched up to make it work.