Basic AVR flashing LED program is not working
PORTB &amp;= -(1&lt;&lt;PB0); should be PORTB &amp;= ~(1&lt;&lt;PB0);. 

~(1&lt;&lt;PB0) is 0xFE, which turns off bit 0. -(1&lt;&lt;PB0) is 0xFF, which works out to a no-op, so the pin is never getting turned off.