iverilog/vvp/opcodes.txt

/*
 * Copyright (c) 2001 Stephen Williams (steve@icarus.com)
 *
 *  $Id: opcodes.txt,v 1.8 2001/03/31 01:59:59 steve Exp $
 */



EXECUTABLE INSTRUCTION OPCODES

Instruction opcodes all start with a % character and have 0 or more
operands. In no case are there more then 3 operands. This chapter
describes the specific behavior of each opcode, in hopefully enough
detail that its complete effect can be predicted.

* %add <bit-l>, <bit-r>, <wid>

This instruction adds the right vector into the left vector, the
vectors having the width <wid>. If any of the bits of either vector
are x or z, the result is x. Otherwise, the result is the arithmetic
sum.

* %assign <var-label>, <delay>, <bit>

This does a non-blocking assignment to a variable. The <label>
identifies the affected variable, and the <delay> gives the delay when
the assignment takes place. The delay may be 0. For blocking
assignments, see %set. The <bit> is the address of the thread register
that contains the bit value to assign.

* %cmp/u <bit-l>, <bit-r>, <wid>
* %cmp/s <bit-l>, <bit-r>, <wid>

These instructions perform a generic comparison of two vectors of equal
size. The <bit-l> and <bit-r> numbers address the least-significant
bit of each vector, and <wid> is the width. If either operator is 0,
1, 2 or 3 then it is taken to be a constant replicated to the selected
width.

The results of the comparison go into bits 4, 5, 6 and 7:

	4: eq  (equal)
	5: lt  (less than)
	6: eeq (case equal)

The eeq bit is set to 1 if all the bits in the vectors are exactly the
same, or 0 otherwise. The eq bit is true if the values are logically
the same. That is, x and z are considered equal. In other words the eq
bit is the same as ``=='' and the eeq bit ``===''.

The lt bit is 1 if the left vector is less then the right vector, or 0
if greater then or equal to the right vector. It is the equivilent of
the Verilog < operator. Combinations of these three bits can be used
to implement all the Verilog comparison operators.

The %cmp/u and %cmp/s differ only in the handling of the lt bit. The
%cmp/u does an unsigned compare, whereas the %cmp/s does a signed
compare.

* %cmp/z <bit-l>, <bit-r>, <wid>
* %cmp/x <bit-l>, <bit-r>, <wid>

These instructions are for implementing the casez and casex
comparisons. These work similar to the %cmp/u instructions, except
only an eq bit is calculated. These comparisons both treat z values in
the left or right operand as don't care positions. The %cmp/x
instruction will also treat x values in either operand as don't care.

Only bit 4 is set by these instructions.

* %delay <delay>

This opcode pauses the thread, and causes it to be rescheduled for a
time in the future. The <amount> is the number of the ticks in the
future to reschedule, and is >= 0. If the %delay is zero, then the
thread yields the processor for another thread, but will be resumed in
the current time step.

* %fork <code-label>

This instruction is similar to %jmp, except that it creates a new
thread to start executing at the specified address. The new thread is
created and pushed onto the child stack.  It is also marked runnable,
but is not necessarily started until the current thread yields.

The %fork instruction has no effect other then to push a child thread.

See also %join.


* %inv <bit>, <wid>

Perform a bitwise invert of the vector starting at <bit>. The result
replaces the input. Invert means the following, independently for each
bit:

	0  --> 1
	1  --> 0
	x  --> x
	z  --> x


* %jmp <code-label>

The %jmp instruction performs an unconditional branch to a given
location. The parameter is the label of the destination instruction.

* %jmp/[01xz] <code-label>, <bit>

This is a conditional version of the %jmp instruction. In this case,
a single bit (addressed by <bit>) is tested. If it is one of the
values in the part after the /, the jump is taken. For example:

	%jmp/xz T_label, 8;

will jump to T_label if bit 8 is x or z.

* %join

This is the partner to %fork. This instruction causes the thread to
wait for the top thread in the child stack to terminate, then
continues. It has no effect in the current thread other then to wait
until the top child is cleared.

It is an error to execute %join if there are no children in the child
stack. If a child thread terminates before this instruction is called,
it remains in the stack as a zombie until the %join reaps it.

If a thread terminates (i.e. executes %end) all its children are
terminated as well.


* %load <bit>, <functor-label>

This instruction loads a value from the given functor output into the
specified thread register bit.

* %mov <dst>, <src>, <wid>

This instruction copies a vector from one place in register space to
another. The destination and source vectors are assumed to be the same
width and non-overlapping. The <dst> may not be 0-3, but if the <src>
is one of the 4 constant bits, the effect is to replicate the value
into the destination vector. Useful for filling a vector.

* %set <var-label>, <bit>

This sets a bit of a variable, and is used to implement blocking
assignments. The <label> identifies the variable to receive the new
value. Once the set completes, the value is immediately available to
be read out of the variable. The <bit> is the address of the thread
register that contains the bit value to assign.

* %vpi_call <name> [, ...]

This instruction makes a call to a system task or function that was
declared using VPI. The operands are compiled down to a vpiHandle for
the call. The instruction contains only the vpiHandle for the
call. See the vpi.txt file for more on system task/function calls.

* %wait <functor-label>

When a thread executes this instruction, it places itself in the
sensitive list for the addressed functor. The functor holds all the
threads that await the functor. When the defined sort of event occurs
on the functor, a thread schedule event is created for all the threads
in its list and the list is cleared.

/*
 * Copyright (c) 2001 Stephen Williams (steve@icarus.com)
 *
 *    This source code is free software; you can redistribute it
 *    and/or modify it in source code form under the terms of the GNU
 *    General Public License as published by the Free Software
 *    Foundation; either version 2 of the License, or (at your option)
 *    any later version.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    GNU General Public License for more details.
 *
 *    You should have received a copy of the GNU General Public License
 *    along with this program; if not, write to the Free Software
 *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
 */