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Optimize 1MHz and 32KHz use cases 

Add optimizations for the most common use cases of the
us ticker, 1MHz,  and the lp ticker, 32KHz.
pull/5028/head
Russ Butler 2017-09-18 17:52:57 -05:00
parent ec55b82acf
commit 0d3714e9b7
1 changed files with 50 additions and 10 deletions
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60
hal/mbed_ticker_api.c
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@ -121,14 +121,35 @@ static void update_present_time(const ticker_data_t *const ticker)
uint64_t elapsed_ticks = (ticker_time - queue->tick_last_read) & queue->bitmask;
queue->tick_last_read = ticker_time;
uint64_t us_x_ticks = elapsed_ticks * 1000000;
uint64_t elapsed_us = us_x_ticks / queue->frequency;
uint64_t elapsed_us;
if (1000000 == queue->frequency) {
// Optimized for 1MHz
// Update remainder
queue->tick_remainder += us_x_ticks - elapsed_us * queue->frequency;
if (queue->tick_remainder >= queue->frequency) {
elapsed_us += 1;
queue->tick_remainder -= queue->frequency;
elapsed_us = elapsed_ticks;
} else if (32768 == queue->frequency) {
// Optimized for 32KHz
uint64_t us_x_ticks = elapsed_ticks * 1000000;
elapsed_us = us_x_ticks >> 15;
// Update remainder
queue->tick_remainder += us_x_ticks - (elapsed_us << 15);
if (queue->tick_remainder >= queue->frequency) {
elapsed_us += 1;
queue->tick_remainder -= queue->frequency;
}
} else {
// General case
uint64_t us_x_ticks = elapsed_ticks * 1000000;
elapsed_us = us_x_ticks / queue->frequency;
// Update remainder
queue->tick_remainder += us_x_ticks - elapsed_us * queue->frequency;
if (queue->tick_remainder >= queue->frequency) {
elapsed_us += 1;
queue->tick_remainder -= queue->frequency;
}
}
// Update current time
@ -146,9 +167,28 @@ static timestamp_t compute_tick(const ticker_data_t *const ticker, us_timestamp_
timestamp_t delta = ticker->queue->max_delta;
if (delta_us <= ticker->queue->max_delta_us) {
// Checking max_delta_us ensures the operation will not overflow
delta = delta_us * queue->frequency / 1000000;
if (delta > ticker->queue->max_delta) {
delta = ticker->queue->max_delta;
if (1000000 == queue->frequency) {
// Optimized for 1MHz
delta = delta_us;
if (delta > ticker->queue->max_delta) {
delta = ticker->queue->max_delta;
}
} else if (32768 == queue->frequency) {
// Optimized for 32KHz
delta = (delta_us << 15) / 1000000;
if (delta > ticker->queue->max_delta) {
delta = ticker->queue->max_delta;
}
} else {
// General case
delta = delta_us * queue->frequency / 1000000;
if (delta > ticker->queue->max_delta) {
delta = ticker->queue->max_delta;
}
}
}
return (queue->tick_last_read + delta) & queue->bitmask;