US2ST with ULL

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pito
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Joined: Sun Nov 06, 2011 3:54 pm

US2ST with ULL

Postby pito » Sun Mar 20, 2016 1:51 pm

While playing with VLdisco demo (cpu @40MHz) I've tried to use

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chThdSleepMicroseconds(2000100);  //2.0001sec


The macro flows over with CH_CFG_ST_FREQUENCY=10000 so I've modified it

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#define US2ST(usec)                                                         \
  ((systime_t)(((((uint64_t)(usec)) *                                       \
                 ((uint64_t)CH_CFG_ST_FREQUENCY)) + 999999ULL) / 1000000ULL))


and it blinks as expected now :) .

PS: I would do it with MS2ST too, as t>429secs with CH_CFG_ST_FREQUENCY=10000 will overflow as well (and those values are quite realistic).
PPS: and finally a check of the resulting macro value against the tick timer size (16 or 32bit) may help too..

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Giovanni
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Re: US2ST with ULL

Postby Giovanni » Tue Mar 22, 2016 3:07 pm

The problem is that if you pass to the macro a variable then it would do 64 bits arithmetic at runtime.

It is a real problem, both solution are not perfect.

Giovanni


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