The
plloutdiv
register controls a clock divider that divides the output of the PLL.
plloutdiv: PLL Final Divide Configuration (
plloutdiv
)
Register Offset
0xC
Bits
Field Name
Attr.
Rst.
Description
[5:0]
plloutdiv
RW
0x0
PLL Final Divider Value
[7:6]
Reserved
[13:8]
plloutdivby1
RW
0x1
PLL Final Divide By 1
[31:14]
Reserved
If the
plloutdivby1
bit is set, the PLL output clock is passed through undivided. If
plloutdivby1
is clear, the value
in
plloutdiv
sets the clock-divide ratio to
(between 2–128). The output divider expands the PLL output frequency range to
0.375–384 MHz.
The
plloutdivby1
register is reset to divide-by-1 (
plloutdivby1
=1).
Internal Programmable Low-Frequency Ring Oscillator
A second programmable ring oscillator (LFROSC) is used to provide an internal low-frequency
32 kHz clock source. The LFROSC can generate frequencies in the range 1.5–230 kHz
(±45%).
The
lfrosccfg
register lives in the AON block as shown in Table 35.
At power-on reset, the LFROSC resets to selecting the middle tap (
lfrosctrim
=16) and ÷5
(
lfroscdiv
=4), resulting in an output frequency of
30 kHz.
The LFROSC can be calibrated in software using a more accurate high-frequency clock source.
lfrosccfg: Ring Oscillator Configuration and Status (
lfrosccfg
)
Register Offset
0x70
Bits
Field Name
Attr.
Rst.
Description
Table 13:
plloutdiv: PLL Final Divide Configuration
Table 14:
lfrosccfg: Ring Oscillator Configuration and Status
Chapter 6 Clock Generation
FE310-G003 Manual
© SiFive, Inc.
Page 31
Содержание FE310-G003
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