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Platform-independent core collection
Commit 7d76d2b6 authored by Tristan Gingold's avatar Tristan Gingold
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Merge branch 'add_scoped_xdc' into 'proposed_master' 

Add scoped XDC constraints for CDC modules

See merge request !16
parents 93195673 f7f3caf9
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README.md
View file @ 7d76d2b6
......@@ -44,6 +44,13 @@ In [modules/common](modules/common) there are general purpose cores:
contains a complex handling for asynchronous signals (crossing clock
domains, deglitcher, edge detection, pulse extension...)
* CDC modules come also with specific timing contraints in [modules/common/xdc](modules/common/xdc).
These constraints can be used in Vivado projects (so-called "module-bound" constraints)
to automatically derive proper timing constraints for CDC paths in each module.
To use it, add specific constraint file to your project and set `SCOPED_TO_REF`
property in GUI or your TCL file.
(e.g. add `gc_sync.xdc` if you use `gc_sync.vhd` and set `SCOPED_TO_REF=gc_sync`)
* For reset generation, you can use [gc_reset](modules/common/gc_reset.vhd)
which generate synchronous resets once all the PLL lock signals are set.
The module [gc_reset_multi_aasd](modules/common/gc_reset_multi_aasd.vhd)
......
modules/common/xdc/gc_reset_multi_aasd.xdc 0 → 100644
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# the "-quiet" option is added for the use case where this module is added to
# the project, but not instatiated (e.g. because of generic settings)
# in that case Vivado would throw critical warnings during P&$
set_false_path -quiet -to [get_pins -hierarchical *rst_chains_reg[*]/CLR]
modules/common/xdc/gc_sync.xdc 0 → 100644
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# Timing constrains for basic 1 bit synchroniser.
# In many cases this could be solved with simple set_false_path, but in some
# cases this module is used in more time-critical applications, eg. inferred FIFO.
# In that case it makes sense to apply some max_delay constraint.
#
# You can always override any of these max_delay constraints in your global XDC
# with set_false_path because it has the highest priority.
set clk [get_clocks -of_objects [get_ports clk_i]]
set clk_period [get_property PERIOD $clk]
# ATTENTION: we can't use "all_fanin" to find the source register because
# apparently this command doesn't traverse outside of scoped reference (even with -flat switch)
# This method won't work properly if there's a combinational path between a source and target FF;
# but in a proper CDC circuit it's forbidded to have logic between FFs anyway!
set dst_ff [get_pins sync_*.sync0_*/D]
set src_ff [get_cells -of_objects [get_pins -filter {IS_LEAF && DIRECTION == OUT} -of_objects [get_nets -segments -of_objects $dst_ff]]]
# We use -quiet switch, because otherwise Vivado will throw critical warning
# if module is not used in the project (e.g. due to generics)
set_max_delay $clk_period -quiet -datapath_only -from $src_ff -to $dst_ff
modules/common/xdc/gc_sync_register.xdc 0 → 100644
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# Timing constrains for basic bit vector synchroniser.
#
# This is similar to gc_sync, but vector synchronisation is usually more tricky.
# Usually you really want to limit bus skew and delay to one clock cycle.
#
# You can always override any of these max_delay constraints in your global XDC
# with set_false_path because it has the highest priority.
set clk [get_clocks -of_objects [get_ports clk_i]]
set clk_period [get_property PERIOD $clk]
# ATTENTION: we can't use "all_fanin" to find the source register because
# apparently this command doesn't traverse outside of scoped reference (even with -flat switch)
# This method won't work properly if there's a combinational path between a source and target FF;
# but in a proper CDC circuit it's forbidded to have logic between FFs anyway!
set dst_ff [get_pins sync0_*[*]/D]
set src_ff [get_cells -of_objects [get_pins -filter {IS_LEAF && DIRECTION == OUT} -of_objects [get_nets -segments -of_objects $dst_ff]]]
# We use -quiet switch, because otherwise Vivado will throw critical warning
# if module is not used in the project (e.g. due to generics)
set_max_delay $clk_period -quiet -datapath_only -from $src_ff -to $dst_ff
set_bus_skew $clk_period -quiet -from $src_ff -to $dst_ff
modules/common/xdc/gc_sync_word_rd.xdc 0 → 100644
View file @ 7d76d2b6
# Timing constrains for read word synchronizer.
# Flag handskaking is done by pulse synchroniser submodule which should have its
# own constraint file and thus isn't covered here
set src_clk [get_clocks -of_objects [get_ports clk_in_i]]
set dst_clk [get_clocks -of_objects [get_ports clk_out_i]]
set src_clk_period [get_property PERIOD $src_clk]
set dst_clk_period [get_property PERIOD $dst_clk]
set skew_value [expr {(($src_clk_period < $dst_clk_period) ? $src_clk_period : $dst_clk_period)}]
set src_ff [get_pins gc_sync_word_data*[*]/C]
set dst_ff [get_pins data_out*[*]/D]
# We use -quiet switch, because otherwise Vivado will throw critical warning
# if module is not used in the project (e.g. due to generics)
set_max_delay $skew_value -quiet -datapath_only -from $src_ff -to $dst_ff
set_bus_skew $skew_value -quiet -from $src_ff -to $dst_ff
modules/common/xdc/gc_sync_word_wr.xdc 0 → 100644
View file @ 7d76d2b6
# Timing constrains for write word synchronizer.
# Flag handskaking is done by pulse synchroniser submodule which should have its
# own constraint file and thus isn't covered here
set src_clk [get_clocks -of_objects [get_ports clk_in_i]]
set dst_clk [get_clocks -of_objects [get_ports clk_out_i]]
set src_clk_period [get_property PERIOD $src_clk]
set dst_clk_period [get_property PERIOD $dst_clk]
set skew_value [expr {(($src_clk_period < $dst_clk_period) ? $src_clk_period : $dst_clk_period)}]
set src_ff [get_pins gc_sync_word_data*[*]/C]
set dst_ff [get_pins dat_out*[*]/D]
# We use -quiet switch, because otherwise Vivado will throw critical warning
# if module is not used in the project (e.g. due to generics)
set_max_delay $skew_value -quiet -datapath_only -from $src_ff -to $dst_ff
set_bus_skew $skew_value -quiet -from $src_ff -to $dst_ff
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