User Manual

Apollo3 Blue Datasheet
DS-A3-0p9p1 Page 533 of 909 2019 Ambiq Micro, Inc.
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12.2.2.4 OCTRL Register
Oscillator Control
OFFSET: 0x0000000C
INSTANCE 0 ADDRESS: 0x4000400C
This register includes controls for autocalibration in addition to the RTC oscillator controls.
23:0 ACALCTR 0x0 RO
Autocalibration Counter result. Bits 17 down to 0 of this is feed directly to the
CALRC register if ACAL register in OCTRL register is set to 1024SEC or
512SEC.
Table 766: OCTRL Register
3
1
3
0
2
9
2
8
2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
1
9
1
8
1
7
1
6
1
5
1
4
1
3
1
2
1
1
1
0
0
9
0
8
0
7
0
6
0
5
0
4
0
3
0
2
0
1
0
0
RSVD ACAL
OSEL
FOS
RSVD
STOPRC
STOPXT
Table 767: OCTRL Register Bits
Bit Name Reset RW Description
31:11 RSVD 0x0 RO
RESERVED
10:8 ACAL 0x0 RW
Autocalibration control. This selects the source to be used in the autocali-
bration flow. This flow can also be used to measure an internal clock
against an external clock source, with the external clock normally used as
the reference.
DIS = 0x0 - Disable Autocalibration
1024SEC = 0x2 - Autocalibrate every 1024 seconds. Once autocalibration
is done, an interrupt will be triggered at the end of 1024 seconds.
512SEC = 0x3 - Autocalibrate every 512 seconds. Once autocalibration is
done, an interrupt will be trigged at the end of 512 seconds.
XTFREQ = 0x6 - Frequency measurement using XT. The XT clock is nor-
mally considered much more accurate than the LFRC clock source.
EXTFREQ = 0x7 - Frequency measurement using external clock.
7OSEL 0x0RW
Selects the RTC oscillator (1 => LFRC, 0 => XT)
RTC_XT = 0x0 - RTC uses the XT
RTC_LFRC = 0x1 - RTC uses the LFRC
6FOS 0x0RW
Oscillator switch on failure function. If this is set, then LFRC clock source
will switch from XT to RC.
DIS = 0x0 - Disable the oscillator switch on failure function.
EN = 0x1 - Enable the oscillator switch on failure function.
Table 765: ACALCTR Register Bits
Bit Name Reset RW Description