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Freescale Semiconductor, Inc.
LIN Stepper Software Description
LIN Stepper Software Implementation
UWord16 variable frequencyActLowHigh.Word. This will guarantee
the low resolution (necessary to create low steepness frequency ramps).
For the frequency-to-period calculation and comparison with required
frequency frequencyReq, it is sufficient to use 8-bit information. This
allows to use fast calculations like frequency to speed conversion using
udiv16_8to16.
Then the high byte frequencyActLowHigh.Byte.High is accessed.
Freescale Semiconductor, Inc...
6.3.4 Actual Frequency to Period Conversion
The conversion from frequency to period requires division.
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Period = --------------------------Frequency
(EQ 19.)
For software execution optimized calculation we wrote a special
arithmetic function:
UWord16 udiv16_8to16(UWord16 x, UByte y)
with UWord16 output and UWord16 x, UByte y inputs. It is written in
assembler and provides the following calculation:
Variable1UWord16 Variable3 = UWord16
-----------------------------------------------UByte Variable3
(EQ 20.)
The conversion must take into account the variables scaling:
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Resolution Period*(UWord16) periodStep = --------------------------------------------------------------------------------------------------------Resolution Frequency*(UByte8) Frequency
(EQ 21.)
UWord16 ) ( Resolution Frequency/ResolutionPeriod )(UWord16) periodStep = (----------------------------------------------------------------------------------------------------------------------------------(UByte8) Frequency
(EQ 22.)
So the final calculation using the udiv16_8to16 function is:
( UWord16 ) ( CONVERSION_CONST_PERIOD_FERQ -)
(UWord16) periodStep = ------------------------------------------------------------------------------------------------------------------------------------------(UByte8) frequencyActLowHigh.Byte.High
(EQ 23.)
where:
Resolution Period [s] is RESOLUTION_PERIOD_NS*1000000000.0
DRM047 — Rev 0
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Designer Reference Manual
LIN Stepper Software Description
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