Thread: Please explain what this macro is doing

Hello,

I am working with PIC32CM controller using Harmony3 framework. Can someone explain the following use of the language:

//Macro defined:
#define LED_Set() (PORT_REGS->GROUP[0].PORT_OUTSET = ((uint32_t)1U << 24U))

I understand it is a function-like macro, but when it is called in main.c, another macro sets it this way

#define LED_Off LED_Set

Why parenthesis are missing from LED_Set?

and finally it is called LED_Off(); in a function inside main().

All these uses/not-use of parenthesis are not making sense. Please help.

Thanks,

BTW: If someone is experienced with PIC32CM1216MC000xx or similar microcontroller, I am willing to pay for their time to answer my questions any reasonable price. Though I am not an expert, I understand C-language but having difficulty decoding statements like (PORT_REGS->GROUP[0].PORT_OUTSET = ((uint32_t)1U << 24U)). Please contact me via email.

Code:

LED_Off();

becomes...

Code:

LED_Set();

which becomes

Code:

(PORT_REGS->GROUP[0].PORT_OUTSET = ((uint32_t)1U << 24U));

Sort of like a copy and paste thing

This...

Code:

((uint32_t)1U << 24U));

is saying that the unsigned 32 bit number 1 is shifted to the left 24 times.
i.e.

Code:

0000 0000 0000 0000 0000 0000 0000 0001 << 24
=
0000 0001 0000 0000 0000 0000 0000 0000

It is the way of setting an individual bit in a portable way.

The 'U' is saying to the compiler that this number is an unsigned int

PORT_REGS is a pointer, that's why you need to use ->

You appear to have different output groups, and they are organised into different array elements. Each one of those elements has a member called PORT_OUTSET, which would be related to the output ports of your device.

Wow! Laserlight. Very well explained.

The compiler behaves exactly as you have suggested for the alternate uses of parenthesis:

#define LED_Off LED_Set() --- but now have to leave out the parenthesis when using the LED_Off in the main code.
or
#define LED_Off() LED_Set() --- use parenthesis with both the name and the declaration and also use parenthesis when using the LED_Off() in the main code.

Thanks for your great help!

Hi Click_here,

Thanks for explaining the statement with example. I appreciate your help.
For some reason, when I click on reply, the cart-wheel appears but page does not transition - must be some bug.

I understand the bit-shifting statement, but having difficulty with statements prior to bit-sit statement. I search in the Harmony3 generated code but cannot find what I am looking for.

Thanks again for your help!

Think of it like cut and paste.

If I type...

Code:

LED_Off();

... it will "cut" the "LED_Off" leaving the "();"

Code:

<snip>();

... and replace it with "LED_Set"

Code:

LED_Set();

The next one will also snip the "()"

Code:

LED_Set();
...
<snip>;
...
(PORT_REGS->GROUP[0].PORT_OUTSET = ((uint32_t)1U << 24U));

Thanks Click_here,

Another great explanation.

Boomer