Functional Description - STMicroelectronics SPC572L series Reference Manual

RM0400
Field
0:11 Reserved
Measurement duration bits. This field displays the measurement duration in terms of selected
12:31
clock (CLKMT0_RMN) cycles. This value is loaded in the frequency meter
MD
down-counter. The down-counter starts counting when CMU_CSR [SFM] = 1.
23.5

Functional description

This section describes the functionality of the CMU.
23.5.1 Frequency meter
The purpose of frequency meter is to evaluate the deviation from the nominal metered
source (such as, CLKMT0_RMN) frequencies. This in turn allows either recalibration of
these clocks or other timing corrections. Programming of the CMU_CSR[CKSEL1] field is
used to select one of metered clocks from a multiplexer that drives a simple Frequency
Meter (see
signal. The measurement starts when CMU_CSR[SFM] = 1. The measurement duration is
given by the contents of CMU_MDR[MD] in terms of number of clock cycles of the selected
metered clock. The CMU_CSR[SFM] bit is cleared by hardware once the frequency
measurement is complete and the count is loaded in CMU_FDR[FD]. The frequency of the
selected clock (f
following equation:
Equation 7
23.5.2 CLKMN0_RMT supervisor
If frequency of CLKMN0_RMT is smaller than frequency of
CLKMT0_RMN / 2
then:
•
The CMU writes 1 to CMU_ISR[OLRI].
•
The CMU asserts the OLR signal.
Note: f
CLKMN0_RMT
guarantee correct f
23.5.3 CLKMN1 supervisor
The frequency of CLKMN1(f
CMU_CSR[CME] = 1. CLKMN1 monitoring starts as soon as CMU_CSR[CME] = 1. This
monitor can be disabled at any time by programming CMU_CSR[CME] = 0.
If f
CLKMN1
and CLKMN1 is 'ON' as signaled by the MC_ME, then:
•
The CMU writes 1 to CMU_ISR[FHHI]
•
The CMU asserts the FHH signal
Table 231. CMU_MDR field descriptions
Figure 173). The reference clock for the Frequency Meter is the CLKMN0_RMT
) can be derived from the value loaded in the CMU_FDR as shown in the
sel
f = (f
sel CLKMN0_RMT
CMU_CSR[RCDIV]
must be greater than f
CLKMN0_RMT
CLKMN1
is greater than the reference value determined by fields CMU_HFREFR[HFREF]
DocID027809 Rev 4
Description
x MDR[MD]) / FDR[FD]
and CLKMN0_RMT is 'ON' as signaled by the MC_ME,
RCDIV
/ 2
CLKMT0_RMN
monitoring.
) can be monitored by programming
Clock Monitor Unit (CMU)
by at least 0.5 MHz in order to
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