_delay_ms seems not to work when using pwm - c

Question

I'm relatively new to programming microcontrollers, so I started experimenting on an ATtiny85.
First program was simply turning on an LED and off with a little delay (classic blinky program).
Now I wanted to slowly increase the brightness of the LED. Here is the code:
#define F_CPU 1000000L
#include <avr/io.h>
#include <util/delay.h>
#include <stdint.h>
#define LED PB0
void setup(void);
void loop(void);
void analogOutput(int8_t brightness);
int main(void)
{
setup();
while (1)
{
loop();
}
return 0;
}
void setup()
{
TCCR0A = (1 << WGM00) | (1 << WGM01);
TCCR0B = (1 << CS00) | (1 << CS01);
DDRB = (1 << LED);
PORTB = 0;
}
void loop()
{
int8_t brightness = 0;
analogOutput(brightness);
_delay_ms(500);
for (brightness = 0; brightness < 256; ++brightness)
{
analogOutput(brightness);
_delay_ms(10);
}
}
void analogOutput(int8_t brightness)
{
if (brightness == 0)
{
// digital output LOW
TCCR0A &= ~(1 << COM0A1);
PORTB &= ~(1 << LED);
}
else if (brightness == 255)
{
// digital output HIGH
TCCR0A &= ~(1 << COM0A1);
PORTB |= (1 << LED);
}
else
{
PORTB &= ~(1 << LED);
// analog output
TCCR0A |= (1 << COM0A1);
OCR0A = brightness;
}
}
I expected the LED to be turned off for half a second and then increase the brightness.
But if i run the code the LED simply becomes more bright, as if the _delay_ms(500) was ignored.
The analogOutput function is inspired by the function of the Arduino library.
What is wrong here? Why does the delay not work as expected?
EDIT
I changed my loop function, new content:
void loop()
{
analogOutput(127);
_delay_ms(500);
analogOutput(255);
_delay_ms(500);
}
This works, I now have a LED that constantly switches from dimmed to fully on and back.

Answer 1

__delay_ms() is converted to cycle-wasting instructions by the compiler, so as long as your F_CPU matches the current speed of the processor, then it should work as expected.
I would look for other places in your code that are not working as you expect them to.
A half second delay at power up is not a great diagnostic test since it happens quickly, only once, and there may be other things going on then as well.
Maybe instead try blinking between two different brightness levels with a 500ms delay between. Visually this should be unambiguous.
if that works as expected, then maybe try doing a brightness ramp and changing the delay inside the loop to see if that works as expected.
Eventually you will work your way up to something that is not as expected, and then you will know where the problem is. It is still possible you will not understand what is going on, but at least you will be able to ask a much more specific question here and be more likely to get a helpful answer.
Report back with your results!

Answer 2

I feel stupid.. It was just an overflow error, since I used uint8_t and set < 256 in the for loop, the condition was always true (255 + 1 = 0).
My solution was to use uint16_t for the loop