This patch optimises away straight line sequences like:
wait for 0 ns;
wait for X ns;
to:
wait for X ns;
This tidies up the output a bit.
It also has the effect of removing all code from initial
processes where the assignments have been extracted as
VHDL signal intialisers. (c.f. pr2391337)
This changes the assignment statement generator so that
each VHDL declaration "knows" which type of assignment
statement can/should be used on (i.e. signals must be
assigned with <=). This will help us catch cases when
we try to use, for example, := with signals. This occurs
in pr2362211 where we try to assign to a signal within
a function (where only := can be used).
With this small patch, building succeeds with Debian's current gcc-snapshot,
gcc (Debian 20081130-1) 4.4.0 20081130 (experimental) [trunk revision 142292]
That gcc also warns about the remaining #idents in
vvp/concat.cc
vvp/dff.h
The resulting build shows some regressions in the test suite, that
I am still investigating. The patch does not break building, or show
test suite regressions, with gcc-4.3.
A casex statement cannot be directly translated to a VHDL case
statement as VHDL does not treat the don't-care bit as special.
The solution here is to generate an if statement from the casex
which compares only the non-don't-care bit positions.
Emitting a VHDL expression like Resize("01", 32) is ambiguous
between interpreting "01" as a Signed or an Unsigned. There's
no point actually outputting this as we can sign-extend the
constant value in the code generator, which is what this
patch does.
The exponentiation operator in VHDL is not defined for numeric_std
types. We can get around this by converting the operands to integers,
performing the operation, then converting the result back to the
original type. This will work OK in simulation but certainly will not
synthesise unless the operands are constant.
However, even this does not work quite correctly. The Integer type in
VHDL is signed and usually only 32 bits, therefore any result larger
than this will overflow and raise an exception. I can't see a way
around this at the moment.
This splits up the monolithic and confusing vhdl_expr::cast function into
several smaller to_XXX functions which each generate code to cast an
expression to type XXX. This makes it much easier to understand and maintain.
Previously this was handled by creating an internal
signal that was connected to the output and could also
be read inside the entity. The correct solution is to
make the output `buffer' rather than `out'. However, this
does not work in the case when an output is connected to
an output of a child entity, and that values is read
in the parent. In this case *both* the outputs of the child
and the parent need to be made `buffer'.
This patch adds a forward declaration for every user funciton.
This fixes VHDL compile problems if a function calls another
before it has been declared.
Whilst adding `wait until ...' at the end of every
process is a valid translation of the input, it is not
actually synthesisable in at least one commercial
synthesiser (XST). According to the XST manual the
correct template is to use `wait until ...' at the
start of sequential processes and `wait on ...'
(equivalent to `wait until ...' with 'Event on all
the signals) at the end of combinatorial processes.
This patch implements that.
Initial processes set a magic flag in the code generator
which allows it to push constant assignments into the
VHDL signal initialisation and omit the assignment.
However, it should only do this if the signal has not
already been read (otherwise the previous read would
not get the undefined value as expected)
If output P of A is connected to output Q of B (and A is
instantiated inside B) then VHDL does not allow B to read
the value of Q (also P), but Verilog does. To get around
this the output Q is mapped to P_Sig which is then connected
to P, this allows B to read the value of P/Q via P_Sig.
Nick Gasson
Larry Doolittle