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Optimize LED writes

pull/266/head
D.R.racer 2023-03-08 09:38:35 +01:00
parent 8d40d39701
commit 5cae131cf5
1 changed files with 35 additions and 2 deletions
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37
src/hal/avr/shr16.cpp
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@ -42,8 +42,41 @@ void SHR16::Write(uint16_t v) {
void SHR16::SetLED(uint16_t led) {
ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
led = ((led & 0x00ff) << 8) | ((led & 0x0300) >> 2);
Write((shr16_v & ~SHR16_LED_MSK) | led);
// led = ((led & 0x00ff) << 8) | ((led & 0x0300) >> 2);
// save 12 bytes by rewriting the bit operations into unions ... avr-gcc7 is not very strong in this kind of optimization
// and the Atmega instruction set doesn't help it either
union InputU {
struct __attribute__((packed)) S {
uint8_t l8 : 8;
uint8_t l0 : 1;
uint8_t l1 : 1;
uint8_t empty : 6;
} s;
uint16_t u;
constexpr InputU(uint16_t u)
: u(u) {}
};
static_assert(sizeof(InputU) == 2);
union OutputU {
struct __attribute__((packed)) S {
uint8_t empty : 6;
uint8_t l0 : 1;
uint8_t l1 : 1;
uint8_t l8 : 8;
constexpr explicit S(InputU iu)
: empty(0)
, l0(iu.s.l0)
, l1(iu.s.l1)
, l8(iu.s.l8) {}
} s;
uint16_t u;
constexpr OutputU(InputU iu)
: s(iu) {}
};
static_assert(sizeof(OutputU) == 2);
Write((shr16_v & ~SHR16_LED_MSK) | OutputU(InputU(led)).u);
}
}