CXD5602 User Manual
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866/1010
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The following table shows the estimated values of time stamp fluctuation (maximum) when a task’s execution
start time is affected by the presence of a different task. (in this table, the SCU clock is RCOSC 8.192 MHz)
Table SCU (Sensor Control Unit)-727 Time Stamp Fluctuation Estimated Values
Task
Number of Fluctuation Clocks
Time Stamp Fluctuation (maximum)
(1/32768 seconds)
HPADC
2737
11
LPADC
3907
16
SPI
3794
16
I2C
4259
18
Figure SCU (Sensor Control Unit)-92 shows a case when fluctuation is caused by the effects of HPADC. In this
example, the fluctuation is approximately 7 (32 kHz count) in Table SCU (Sensor Control Unit)-734. Note that in
the below Figure, the fluctuation of the sequencer start time is not considered.
the case of fetching
HPADC data
the case of not
fetching HPADC data
HPADC
SPI
I2C0
I2C1
LPADC
SPI
I2C0
I2C1
LPADC
the variation of
time stamp for SPI
Figure SCU (Sensor Control Unit)-92 Time Stamp Fluctuation by the Presence/Absence of HPADC Execution
3.9.15.13
Time Stamp Readout Restrictions
The time stamp within the SCU is comprised of MSB 32 bits (the seconds digits) and LSB 15 bits (the seconds
and smaller than seconds digits). However, atomic access is not supported during readout from the APB.
Therefore, when readout is performed by APB access two times, the time stamp readout value may shift by a
maximum of ±1 seconds.
Within the hardware, “LSB and MSB, and remaining number of FIFO data update are atomic” is compensated for.
Therefore, the only problem is when update occurs during two bus accesses, which can be avoided by performing
two continuous readouts (four APB accesses).
The following is an example pseudo code of reading out the OLDEST_TIMESTAMP two times. Using the
change of the MSB, the carry of the MSB during the two bus accesses is detected.
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