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1.添加安全补丁和具体注释。

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MacRsh
2024-01-21 01:11:28 +08:00
parent 28e6be3f89
commit 802444700d
1 changed files with 11 additions and 16 deletions
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27
device/pwm.c
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@@ -69,7 +69,7 @@ static int pwm_calculate(struct mr_pwm *pwm, uint32_t freq)
int error_min = INT32_MAX; int error_min = INT32_MAX;
/* Check the clock and frequency */ /* Check the clock and frequency */
if (clk == 0 || freq == 0) if ((clk == 0) || (freq == 0))
{ {
return MR_EINVAL; return MR_EINVAL;
} }
@@ -81,28 +81,29 @@ static int pwm_calculate(struct mr_pwm *pwm, uint32_t freq)
if (product <= per_max) if (product <= per_max)
{ {
psc_best = 1; psc_best = 1;
per_best = product; per_best = MR_BOUND(product, 1, per_max);
} else } else
{ {
/* Calculate the Least error prescaler and period */ /* Calculate the least error prescaler and period */
for (uint32_t psc = MR_BOUND(product / per_max, 1, psc_max); psc < psc_max; psc++) for (uint32_t psc = MR_BOUND(product / per_max, 1, psc_max); psc < psc_max; psc++)
{ {
uint32_t per = MR_BOUND(product / psc, 1, per_max); uint32_t per = MR_BOUND(product / psc, 1, per_max);
/* Calculate the frequency error */ /* Calculate the frequency error */
int error = (int)freq - (int)(clk / psc / per); int error = (int)((clk / psc / per) - freq);
/* Found a potentially optimal prescaler and period combination */ /* Found a valid and optimal solution */
if (error == 0) if (error == 0)
{ {
psc_best = psc; psc_best = psc;
per_best = per; per_best = per;
break;
/* Found a valid and optimal solution */ /* Error could only be >= 0 because:
if (per_best < per_max) * <product> is floored during calculation, making it smaller,
{ * smaller <product> leads to smaller <per>,
break; * smaller <per> means <clk / psc / per> is lower than <freq>
} */
} else if (error < error_min) } else if (error < error_min)
{ {
error_min = error; error_min = error;
@@ -112,12 +113,6 @@ static int pwm_calculate(struct mr_pwm *pwm, uint32_t freq)
} }
} }
/* Check period is valid */
if (per_best > per_max)
{
return MR_EINVAL;
}
pwm->prescaler = psc_best; pwm->prescaler = psc_best;
pwm->period = per_best; pwm->period = per_best;
pwm->freq = clk / psc_best / per_best; pwm->freq = clk / psc_best / per_best;