Requirements for rxsys_clk – Altera POS-PHY Level 4 IP Core User Manual
Page 49
Chapter 4: Functional Description—Receiver
4–11
Clock Structure
December 2014
Altera Corporation
POS-PHY Level 4 IP Core User Guide
In 32-bit (quarter-rate) SPI-4.2 mode, all the above clocks exist. The maximum
frequency of the clocks depends on ALTDDIO_IN limitations. To minimize clock
skews, the rdclk goes into a PLL where it generates rdint_clk (×1). The PLL is
required to provide 90 phase shift, so the ALTDDIO_IN IP core samples in the centre
of the data eye. A typical system may have a rdint_clk of 100 MHz, of which the SPI-
4.2 data rate is 200 Mbps. Most of the quarter-rate receiver IP core runs off rdint_clk,
including all data path processors and the write side of the FIFO buffer.
Figure 4–5
shows the clocking structure used by the receiver IP core, for 32-bit (quarter-rate
mode) variations that use the ALTDDIO_IN IP core.
Requirements for rxsys_clk
The IP core’s protocol logic and all Atlantic FIFO buffers share a common clock called
rxsys_clk
that clocks both the write and optionally the read side of the Atlantic FIFO
buffers.
Table 4–2
shows guidelines for the frequency of rxsys_clk.
f
For detail on the optimum setting of rxsys_clk, refer to
Figure 4–5. Clock Layout Diagram (Quarter Rate)
Notes to
Figure 4–5
:
(1) rxsys_clk is internally connected to rdint_clk in 32-bit shared buffer with embedded addressing mode variations.
(2) The single clock mode removes the separate Atlantic clocks.
(3) The embedded address mode has only one buffer; the individual buffers mode can have more than one buffer.
(4) In 32-bit (quarter-rate) SPI-4.2 mode, this PLL only provides a phase shift for the incoming rdclk.
ALTDDIO_IN
ALTDDIO_OUT
EPLL
(Note 4)
Status
Processor
Data
Processor
Atlantic
Buffer 0
Atlantic
Interface 0
a0_arxclk
aN_arxclk
(Note 2, 3)
rdclk
ctl_rx_pll_areset
stat_rx_pll_locked
rdat[15:0]
rctl
rxsys_clk
(Note 1)
rdint_clk
rsclk
rstat[1:0]
Atlantic
Buffer N
Atlantic
Interface N
2
Table 4–2. Frequency Guidelines—rxsys_clk
Data Path Width
(Bits)
Worst Case Frequency Requirement
32
1.0 × rdint_clk
64
1.25 × rdint_clk
128
1.6 × rdint_clk