Re: [avr-libc-dev] RFC: avr/bits.h

[Nicolas Schodet]

Hello,

About bit manipulations, I had a bad experience last week. On some
registers, bit manipulation can be tricky:

TWCR &= ~(_BV (TWSTA) | _BV (TWSTO));

The interrupt flag bit is read as 1, and writen at 1, this clear the
interrupt bit! A warning could be added to the manual.


Another question about bit manipulation: what is the best way to read 4
bytes into a double word? This could also be included in the bit
manipulation header. This code seems to compile quite bad and generate
useless operations:

uint32_t a;
uint8_t b[4];

a = (uint32_t) b[0] << 24 | (uint32_t) b[1] << 16
    | (uint32_t) b[2] << 8 | (uint32_t) b[3] << 0;

Thanks!

Nicolas.