1. Purpose of Constraint
Introduce the principle of FPGA constraints, understand the purpose of constraints for design services, is to ensure that the design meets timing requirements, and guide FPGA tools for synthesis and implementation. Constraints are the goals that Vivado and other tools strive to achieve. Therefore, the design must be reasonable before the constraints can be satisfied. The constraints in turn check whether the design can meet the timing. It mainly involves the xilinx vivado xdc constraint syntax and gives the corresponding ISE ucf syntax. In addition, the quatus syntax is almost compatible with xdc, the principle is the same.
The most basic of timing constraints is the clock, which has three characteristics: jitter, skew, and duty cycle distortion.
1. Jitter is divided into cycle jitter, cycle to cycle jitter and long term jitter.
2. The offset is related to the length of the clock line, the load capacitance of the timing unit and the number. The global clock of FPGA adopts all copper technology and tree structure, the deviation is very small and can be ignored.
3. Duty cycle distortion is high- and low-level asymmetry, which will consume the timing margin.
2. Basic clock constraints
In the simplest case, the design has only one clock. At this time, the period of this clock needs to be constrained, (of course, the duty cycle can also be constrained, the default is 50%). If we don't constrain the clock, we don't know whether our design has closed timing. Simply put, for example, if the system clock is 200M, then the period is 5ns, which means that the signal comes out of a register and goes through a series of combinational logic. It must be sampled by the destination register before the rising edge of the next clock. Of course, considering that the actual situation is much more complicated.
If there are many clocks in the design, which clocks must be constrained?
The first is the clock that enters the FPGA from the port. Other derived clocks (such as those generated by PLL or MMCM) are homologous clocks, and the tool will automatically derive them. Then, GT's rx_clk and tx_clk must be constrained. Finally, the traveling wave clock generated by the user's own frequency division (for simple low frequency applications) must be constrained.
create_clock -name clk_200m -period 5 [get_ports I_clk200]
3. Cross-clock domain cdc constraints
set_clock_groups –asynchronous -group [get_clocks -include_generated_clocks clk_1] \
-group [get_clocks -include_generated_clocks clk_2]
4. input delay
Both input delay and output delay are external delays analyzed, which is the exact opposite of ISE's ucf-constrained FPGA internal delay.
5. output delay
Assume the period is 10ns
OFFSET = OUT 4ns AFTER clock;
set_output_delay 6 -clock ï¼»get_clocksï¼½ ï¼»get_portsï¼½
By putting the input output register pack into the IOB, and constraining slew, it is easier to meet the interface timing requirements.
constraints in rtl
(* IOB = "true" *)
O_config_dat
constraints in xdc
set_property IOB true [get_ports O_config_dat]
set_property SLEW FAST [get_ports O_config_dat]
What is Feeder on the placement machine? What is Feida on the placement machine? Feida is the main accessory of the placement machine. Its function is to mount the SMD patch components on the feeder, and the feeder provides components for the placement machine for patching.
In the placement machine, the feeder functions to supply the chip component SMC/SMD to the placement head in a regular pattern and order for accurate and convenient pickup, which occupies a large number and position in the placement machine. It is also an important part of choosing a placement machine and arranging the placement process. Depending on the SMC/SMD package, feeders typically have a variety of tapes, sticks, waffles, and bulk materials.
Tape feeders with the different size such as 8mm, 16mm, 24mm, 32mm, 44mm, 56mm etc.Panasonic Feeder,Insertion Machine Tape Feeder Unit,Tape Feeder Unit,Feeder Panasonic
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