3.3. Clash Compiler Flags¶
- --vhdl
Use the VHDL backend for code generation. This currently emits VHDL 1993 source which can be consumed by other tools.
- --verilog
Use the Verilog backend for code generation. This currently emits Verilog 2001 source which can be consumed by other tools.
- --systemverilog
Use the SystemVerilog backend for code generation. This currently emits SystemVerilog 2012 source which can be consumed by other tools.
- -fclash-debug
Set the debugging mode for the compiler, exposing additional output. The available options are
DebugNone
to show no debug messagesDebugSilent
to test invariants and error if any are violated. This is implicitly enabled by any debug flagDebugFinal
to show expressions after they have been completely normalizedDebugCount
to count how often each transformation is appliedDebugName
to show the names of transformations as they are appliedDebugTry
to show names of tried and applied transformationsDebugApplied
to show sub-expressions after they are rewrittenDebugAll
to show all sub-expressions when a rewrite is attempted
Default:
DebugNone
Note
This flag exists for backwards compatibility. It is now possible to set debugging flags individually with -fclash-debug-invariants, -fclash-debug-info and -fclash-debug-count-transformations.
- -fclash-debug-invariants
Check invariants while debugging and print warnings / errors which may be useful, such as alterting when unexpected changes occur or when a transformation introduces free variables / shadowing.
- -fclash-debug-info
Specify the information to show about individual transformations while debugging. From least to most information, these are
None
to show no informationFinalTerm
to show the final result of normalizationAppliedName
to show the names of applied transformationsAppliedTerm
to show the result of applied transformationsTryName
to show the names of attempted transforamtions, as well as the result of any transformations which are appliedTryTerm
to show the names and results of all transformations attempted whether they were applied or notDefault:
None
- -fclash-debug-count-transformations
Count the transformations that are applied and print a summary at the end of the normalization phase.
- -fclash-debug-history[=FILENAME]
Saves all applied rewrites into
FILENAME
, for later analysis with the clash-term tool. When no filename is given it defaults tohistory.dat
.
- -fclash-debug-transformations
List the transformations that are to be debugged. This is given as a comma-separated list of transformations, e.g.
clash -fclash-debug-transformations inlineNonRep,topLet,appProp
Default: []
- -fclash-debug-transformations-from=N
Only print debug output from applied transformation
N
and onwards.clash -fclash-debug-transformations-from=21570
Default: 0
- -fclash-debug-transformations-limit=N
Only print debug output for
N
applied transformations.clash -fclash-debug-transformations-limit=12
Default: MAX_INT
- -fclash-hdldir
Specify the directory that generated HDL is written into. For example
clash -fclash-hdldir build/hdl
will create a directory
build/hdl
Default: Either
vhdl
,verilog
, orsystemverilog
depending on the synthesis target.- -fclash-hdlsyn
Specify the HDL synthesis tool which will be used. Available options are
Vivado
,Quartus
andOther
, but some synonyms for these exist (Xilinx
andISE
are synonyms forVivado
,Altera
andIntel
are synyonyms forQuartus
).Default:
Other
- -fclash-no-cache
Don’t reuse previously generated output from Clash, instead generating HDL from a clean state. While this leads to longer builds, it can be useful in development.
Warning
Previously this flag was called
-fclash-nocache
, however this is now deprecated.Default: Cache generated HDL
- -fclash-no-check-inaccessible-idirs
Check that all include directories (containing primitives) exist when running Clash. If any directory does not exist, an error is thrown.
Default: Check directories
- -fclash-clear
Remove HDL directories before writing to them (if cache can’t be used). By default, Clash will only write to non-empty directories if it can prove all files in it are generated by a previous run. This option applies to directories of the various top entities, i.e., the subdirectories made in the directory passed in with
-fclash-hdldir
.Default: Clean before build
- -fclash-no-prim-warn
Disable warnings for primitives that are annotated with
warnAlways
. This means warnings from annotations like{-# ANN f (warnAlways "This primitive is dangerous") #-}
will not be shown when compiling.
Default: Show warnings
- -fclash-spec-limit
Change the number of times a function can undergo specialization.
Default: 20
- -fclash-inline-limit
Change the number of times a function
f
can undergo inlining inside some other functiong
. This prevents the size ofg
growing dramatically.Default: 20
- -fclash-inline-function-limit
Set the threshold for function size. Below this threshold functions are always inlined (if it is not recursive).
Default: 15
- -fclash-inline-constant-limit
Set the threshold for constant size. Below this threshold constants are always inlined. A value of 0 inlines all constants.
Default: 0
- -fclash-evaluator-fuel-limit
Set the threshold for unfolding potentially non-terminating bindings in the evaluator. A value of 0 only unfolds terminating bindings.
Default: 20
- -fclash-intwidth
Set the bit width for the
Int/Word/Integer
types in the generated HDL. Clash simulation is not affected, and neither are BitPack instances. The only allowed values are 32 or 64.Default: Machine word size (
WORD_SIZE_IN_BITS
)- -fclash-error-extra
Print additional information with compiler errors if it as available. If there is extra information and this flag is not enabled, a message will be printed suggesting this flag.
Default: False
- -fclash-float-support
Enable support for floating point numbers. If this is disabled, Clash will not attempt to convert Float and Double values for hardware.
Default: False
- -fclash-component-prefix
Prefix the names of generated HDl components with a string. For example a component
foo
would be calledxcorp_foo
if run withclash -fclash-component-prefix "xcorp"
Default: “”
- -fclash-old-inline-strategy
The new inlining strategy for Clash inlines all functions which are not marked with
NOINLINE
or a synthesize attribute. The old inlining strategy differed, attempting only to inline functions which were deemed “cheap”. The old inlining strategy may be quicker in practice for some circuits.Default: False
- -fclash-no-escaped-identifiers
Disable extended identifiers, as used in some HDLs like VHDL to allow more flexibility with names. Clash will only generate basic identifiers if this is used.
Default: Escaped identifiers are allowed
- -fclash-lower-case-basic-identifiers
Clash will only generate lower case basic identifiers if this is used. This affects places where the various HDLs only allow basic identifiers to be used, most notably module and file names.
Default: Disabled
- -fclash-compile-ultra
Aggressively run the normalizer, potentially gaining much better runtime performance at the expense of compile time.
Default: False
- -fclash-force-undefined{,0,1}
Set the value to use when an undefined value is inserted into generated HDL. This flag can be suffixed with either 0 or 1 to force use of that bit, or left without a suffix to use a HDL-specific default (e.g.
x
in Verilog).Default: Disabled
- -fclash-aggressive-x-optimization
Remove all undefined branches from case expressions, replacing them with another defined value in the expression. If only one branch is defined, the case expression is elided completely. If no branches are defined the entire expression is replaced with a call to
errorX
.Implies:
-fclash-aggressive-x-optimization-blackboxes
Default: False
- -fclash-aggressive-x-optimization-blackboxes
Allow blackboxes to detect undefined values and change their behavior accordingly. For example, if
register
is used in combination with an undefined reset value, it will leave out the reset logic entirely. This flag is enabled when using-fclash-aggressive-x-optimization
.Default: False
- -fclash-edalize
Generate metadata for use with Edalize. This generates edam.py files in all top entities with the configuration for building that entity. Users still need to edit this file to specify the EDA tool to use, and if necessary the device to target (for Quartus, Vivado etc.)
Default: False
- -main-is
When using one of
--vhdl
,--verilog
, or--systemverilog
, this flag refers to synthesis target. For example, running Clash withclash My.Module -main-is top --vhdl
would synthesizeMy.Module.top
.- -fclash-timescale-precision
Sets the second part of Verilog’s
timescale 100fs/100fs
. E.g., setting this flag to1fs
would make Clash generate Verilog files withtimescale 100fs/1fs
as their header.Default:
100fs