lator or an off-chip crystal oscillator. The off-chip oscillator can also drive the high-frequency
clock directly.
For the FE310-G000, the TileLink bus clock (
tlclk
) is fixed to be the same as the processor
core clock (
coreclk
).
The Always-On block includes a real-time clock circuit that is driven from one of the low-fre-
quency clock sources: an off-chip oscillator (LFOSC) or an an on-chip low-frequency oscillator
(LFROSC).
6.2
PRCI Address Space Usage
PRCI (Power, Reset, Clock, Interrupt) is an umbrella term for platform non-AON memory-
mapped control and status registers controlling component power states, resets, clock selection,
and low-level interrupts, hence the name. The AON block contains registers with similar func-
tions, but only for the AON block units.
Table 4 shows the memory map for the PRCI on the FE310-G000.
Offset
Name
Description
0x0
hfrosccfg
Ring Oscillator Configuration and Status
0x4
hfxosccfg
Crystal Oscillator Configuration and Status
0x8
pllcfg
PLL Configuration and Status
0xC
plloutdiv
PLL Final Divide Configuration
6.3
Internal Trimmable Programmable 72 MHz Oscillator
(HFROSC)
An internal trimmable high-frequency ring oscillator (HFROSC) is used to provide the default
clock after reset, and can be used to allow operation without an external high-frequency crystal
or the PLL.
The oscillator is controlled by the
hfrosccfg
register, which is memory-mapped in the PRCI
address space, and whose format is shown in Table 5.
hfrosccfg: Ring Oscillator Configuration and Status (
hfrosccfg
)
Register Offset
0x0
Bits
Field Name
Attr.
Rst.
Description
Table 4:
SiFive PRCI memory map, offsets relative to PRCI base address.
Table 5:
hfrosccfg: Ring Oscillator Configuration and Status
Chapter 6 Clock Generation
SiFive FE310-G000 Manual: v3p2
© SiFive, Inc.
Page 23
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