30
SiFive E300 Platform Reference Manual, Version 1.0.1
R
eserve
d
31
16
rtchi
15
0
rtclo
31
0
Figure 9.2: RTC counter register pair
rtchi
/
rtclo
R
es
erve
d
31
29
rtcmpip
28
R
es
er
ve
d
27
13
rtcenalways
12
R
eserve
d
11
4
rtcscale
3
0
Figure 9.3: RTC configuration register
rtccfg
The 4-bit
rtcscale
field scales the real-time counter value before feeding to the real-time interrupt
comparator. The value in
rtcscale
is the bit position within the
rtclo
/
rtchi
register pair of the
start of a 32-bit field
rtcs
. A value of 0 in
rtcscale
indicates no scaling, and
rtcs
would then be
equal to
rtclo
. The maximum value of 15 in
rtcscale
corresponds to dividing the clock rate by
2
15
, so for an input clock of 32.768 kHz, the LSB of
rtcs
will increment once per second. The value
of
rtcs
is memory-mapped and can be read as a single 32-bit register over the AON TileLink bus.
The
rtccmpip
interrupt pending bit is read-only.
RTC Compare Register
rtccmp
The
rtccmp
register holds a 32-bit value that is compared against
rtcs
, the scaled real-time clock.
If
rtcs
is greater than or equal to
rtccmp
, the
rtccmpip
interrupt pending bit is set. The
rtccmpip
bit can be cleared down by writing a value to
rtccmp
that is greater than
rtcs
.
rtccmp
31
0
Figure 9.4: RTC counter compare register
rtccmp
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