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Commit ca0d2fb7 authored by Uwe Kleine-König's avatar Uwe Kleine-König Committed by Thierry Reding
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pwm: bcm2835: Improve period and duty cycle calculation



With an input clk rate bigger than 2000000000, scaler would have been
zero which then would have resulted in a division by zero.

Also the originally implemented algorithm divided by the result of a
division. This nearly always looses precision. Consider a requested period
of 1000000 ns. With an input clock frequency of 32786885 Hz the hardware
was configured with an actual period of 983869.007 ns (PERIOD = 32258)
while the hardware can provide 1000003.508 ns (PERIOD = 32787).
And note if the input clock frequency was 32786886 Hz instead, the hardware
was configured to 1016656.477 ns (PERIOD = 33333) while the optimal
setting results in 1000003.477 ns (PERIOD = 32787).

This patch implements proper range checking and only divides once for
the calculation of period (and similar for duty_cycle).

Signed-off-by: default avatarUwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: default avatarLino Sanfilippo <LinoSanfilippo@gmx.de>
Tested-by: default avatarLino Sanfilippo <LinoSanfilippo@gmx.de>
Signed-off-by: default avatarThierry Reding <thierry.reding@gmail.com>
parent a38fd874
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