On 30-10-16 10:55, Juergen Stuber wrote:
On Fri, 28 Oct 2016 10:03:17 +0200
Juergen Stuber <juer...@jstuber.net> wrote:
When you use shift and mask you usually do a single access for
all fields of a register.
Note that you shouldn't do it in two assignments
(I'm seeing this in cpu/stm32l1/periph/gpio.c):
port &= ~mask;
port |= (new_value << shift);
This will result in bigger code and the first assignment will write a
spurious value to the register, which might cause problems.
port = (port & ~mask) | (new_value << shift);
is better. Or
port = (port & ~mask)
| (new_value1 << shift1)
...
| (new_valueN << shiftN);
for multiple fields.
True.
But this would not be a good example for (named) bitfields, because
in this example the bitfield is dynamic. (Depends on runtime value of
pin number.)
--
Kees
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