ECP5 and ECP5-5G High-Speed I/O Interface
Technical Note
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FPGA-TN-02035-1.3
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DQS clocking is used for DDR memory interface implementation. DQS clock spans every 12 to 16 I/O’s include the
DQS pins. Refer to the
section for pinout assignment rules when using DQS clocking.
5.13.
Timing Analysis for High Speed DDR Interfaces
It is recommended that you run Static Timing Analysis in the software for each of the high-speed interfaces. This
section describes the timing preferences to use for each type of interface and the expected trace results. The
preferences can either be entered directly in the .lpf file or through the Design Planner graphical user interface.
The External Switching Characteristics section of
ECP5 and ECP5-5G Family Data Sheet (FPGA-DS-02012)
should be used
along with this section. The data sheet specifies the actual values for these constraints for each of the interfaces.
5.13.1.
Frequency Constraints
It is required that you explicitly specify FREQUENCY (or PERIOD) PORT preferences to all input clocks in the
design. This preference may not be required if the clock is generated out of a PLL or DLL or is input to a PLL or DLL.
5.13.2.
DDR Input Setup and Hold Time Constraints
All of the Receive (RX) interfaces, both x1 and x2 can be constrained with setup and hold preference.
5.13.2.1.
Receive Centered Interface
shows the data and clock relationship for a Receive Centered interface. The clock is centered to the data, so
it comes into the devices with a setup and hold time.
Receive Parameters
CLOCK
DATA
t
SUGDDR
t
HGDDR
t
HGDDR
t
SUGDDR
Figure 5.16. RX Centered Interface Timing
Note:
tSUGDDR = Setup Time, tHOGDDR = Hold Time
In this case, you must specify in the software preference the amount of setup and hold time available. These
parameters are listed in
as tSU_GDDRX1/2 and tHO_GDDRX1/2. These can be directly provided using the
INPUT_SETUP and HOLD preference as –
INPUT_SETUP PORT “DATA” <tSU_GDDRX1/2> ns HOLD <tHO_GDDRX1/2> ns CLKPORT “CLOCK”;
where:
Data = Input Data Port
Clock = Input Clock Port
The external Switching Characteristics section of
ECP5 and ECP5-5G Family Data Sheet (FPGA-DS-02012)
specifies the
MIN setup and hold time required for each of the high-speed interfaces running at MAX speed. These values can be
picked up from the data sheet if the interface is running at MAX speed.
Example:
For GDDRX2_RX.ECLK.Centered Interface running at max speed of 400 MHz, the preference would be –
INPUT_SETUP PORT "datain" 0.320000 ns HOLD 0.320000 ns CLKPORT "clk”;
Note
: Refer to
ECP5 and ECP5-5G Family Data Sheet (FPGA-DS-02012)
for the latest tSUDDR and tHOGDDR numbers.