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Real-Time Clock (RTC)
Copyright © 12/13/06 Marvell
CONFIDENTIAL
Doc. No. MV-TBD-00 Rev. A
December 13, 2006
Document Classification: Proprietary Information
Page 399
Not approved by Document Control. For review only.
Most registers in the RTC controller are read/write registers. Marvell strongly recommends that the operating
system use the core memory-management unit (MMU) protection mechanisms to prevent inadvertent writes to
the RCNR. See the Intel XScale
®
Core Developer’s Manual for more information about the MMU.
Because of the asynchronous nature of the 1-Hz clock relative to the PXA300 processor or PXA310 processor
clock, writes to these registers are controlled by a hardware mechanism that delays the actual write until the data
can be synchronized properly. For multiple writes to RTC counter and alarm registers in quick succession, the
final update to the RTC register may be delayed by a maximum of six 32-kHz clock cycles.
The RTC counter and alarm registers can be read at any time. Reads reflect the value in the register after it
increments or after it is written.
13.6.1
RTC Trim Register (RTTR)
, configures the frequency of the 1-Hz clock. The reset value of this register
(0x0000_7FFF) is such that a perfect 32.768 kHz crystal would result in a 1-Hz clock (see
for
details on how to calculate the value for this register).
The RTTR register is reset only by hardware to ensure the validity of the data written into this register. RTTR[31]
is provided as a lock bit. The data in RTTR can be changed only if RTTR[LCK] is clear. Once RTTR[LCK] is
set, only a hardware reset can clear the RTTR.
This is a read/write register. Ignore reads from reserved bits. Write 0b0 to reserved bits.
Table 13-5. RTTR Bit Definitions
Physical Address
0x4090_000C
RTTR
RTC Controller
User
Settings
Bit
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
8
7
6
5
4
3
2
1
0
LCK
reserved
DEL
CK_DIV
Reset
0
?
?
?
?
?
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Bits
Access
Name
Description
31
R/W
LCK
Lock bit for the RTTR:
0 – Value of RTTR can be overwritten
1 – Value of RTTR can not be overwritten
NOTE:
Once LCK has been set, the value of RTTR can be changed
only after a hardware reset.
30:26
—
—
reserved
25:16
R/W
†
DEL
Trim delete count — the number of 32-kHz clocks to delete when clock
trimming begins.
15:0
R/W
†
CK_DIV
Clock Divider count — the number of 32-kHz clock cycles, plus one, per
1-Hz clock cycle. Minimum value is 0x20.
†
These bit fields can be written to only if RTTR[LCK] is clear.