Inc. Portable Generator User Manual

Using the System Generator Constraints Files 135
System Generator Software Features
The ce2_group contains theblocks operating at twice thesystem period, i.e., the input
register and the up sampler. Here are the corresponding constraints.
# ce2_group and inner group constraint
INST "InReg" TNM = "ce2_group";
INST "Up_Sample" TNM = "ce2_group";
TIMESPEC "TS_ce2_group_to_ce2_group" = FROM "ce2_group" TO
"ce2_group" "TS_clk" * 2;
The ce3_group operates at three times the system period. It contains the down
sampler and the output register, and its constraints are the following.
# ce3_group and inner group constraint
INST "Down_Sample" TNM = "ce3_group";
INST "OutReg" TNM = "ce3_group";
TIMESPEC "TS_ce3_group_to_ce3_group" = FROM "ce3_group" TO
"ce3_group" "TS_clk" * 3;
Group to group constraints establish the relative speeds of the groups. Here are the
constraints that relate the speed of ce2_group to ce1_group.
# Group-to-group constraints
TIMESPEC "TS_ce1_group_to_ce2_group" = FROM "ce1_group" TO
"ce2_group" "TS_clk" * 1;
TIMESPEC "TS_ce1_group_to_ce3_group" = FROM "ce1_group" TO
"ce3_group" "TS_clk" * 1;
TIMESPEC "TS_ce2_group_to_ce1_group" = FROM "ce2_group" TO
"ce1_group" "TS_clk" * 1;
TIMESPEC "TS_ce2_group_to_ce3_group" = FROM "ce2_group" TO
"ce3_group" "TS_clk" * 2;
TIMESPEC "TS_ce3_group_to_ce1_group" = FROM "ce3_group" TO
"ce1_group" "TS_clk" * 1;
TIMESPEC "TS_ce3_group_to_ce2_group" = FROM "ce3_group" TO
"ce2_group" "TS_clk" * 2;
Port timingrequirements canbe set in the parameter dialog boxesfor GatewayIn and
Out blocks. These requirements are translated into port constraints like those shown
below. In this example, the 3-bit DIN input is constrained to operate at its gateway’s
sample rate (corresponding to a period of 20 ns). The 'FAST' attributes indicate that
the ports should be implemented using hardware resources that reduce delay. (The
delay is reduced, but at a cost of increased noise and power consumption.) The
Din_valid lines constrain the companion valid signal that accompanies DIN. For
more information concerning valid signals, see the Hardware Handshaking section.
# Offset in constraints
NET "Din<0>" OFFSET = IN : 20.0 : BEFORE "clk";
NET "Din<1>" OFFSET = IN : 20.0 : BEFORE "clk";
NET "Din<2>" OFFSET = IN : 20.0 : BEFORE "clk";
NET "Din_valid" OFFSET = IN : 20.0 : BEFORE "clk";
NET "Din<0>" FAST;
NET "Din<1>" FAST;
NET "Din<2>" FAST;
NET "Din_valid" FAST;
Checking the Specify IOB Location Constraints option for a Gateway In or Gateway
Out block allows port locations to be specified. The locations must be entered as a