ChibiOS Free Embedded RTOS

Posted: **Mon Jun 21, 2021 3:03 pm**

Hello,

The PWM_FRACTION_TO_WIDTH seems tailored for 16 bits timer :

#define PWM_FRACTION_TO_WIDTH(pwmp, denominator, numerator)                 \
  ((pwmcnt_t)((((pwmcnt_t)(pwmp)->period) *                                 \
               (pwmcnt_t)(numerator)) / (pwmcnt_t)(denominator)))

In case of 32 bits timers, period can be large, and period * numerator can overflow.

Is it possible to replace the three last pwmcnt_t casts by uint64_t casts ?

There will be some runtime overhead, but PWM_FRACTION_TO_WIDTH should not be called from a hot path code.

Alexandre

Posted: **Mon Jun 21, 2021 5:31 pm**

Hi,

HAL runs also on compilers that support no C99 and have no uint64_t types, this solution is problematic. Note that it is what we do in RT for time conversions but we can use C99 on that module.

Giovanni

ChibiOS Free Embedded RTOS

integer overflow with PWM_FRACTION_TO_WIDTH and 32 bits timers

integer overflow with PWM_FRACTION_TO_WIDTH and 32 bits timers

Re: integer overflow with PWM_FRACTION_TO_WIDTH and 32 bits timers