/* * Copyright (c) 2001 Stephen Williams (steve@icarus.com) * * $Id: vthread.txt,v 1.3 2001/05/01 05:00:02 steve Exp $ */ THREAD DETAILS Thread objects in vvp are created by ``.thread'' statements in the input source file. A thread object includes a program counter and private bit registers. The program counter is used to step the processor through the code space as it executes instructions. The bit registers each hold Verilog-style 4-value bits and are for use by the arithmetic operators as they operate. The program counter normally increments by one instruction after the instruction is fetched. If the instruction is a branching instruction, then the execution of the instruction sets a new value for the pc. Instructions that use the bit registers have as an operand a value. There is usually space in the instruction for 2 operands. Instructions that work on vectors pull the vector values from the bit registers starting with the LSB and up. The bit addresses 0, 1, 2 and 3 are special constant bits 0, 1, x and z, and are used as read-only immediate values. If the instruction takes a single bit operand, the the appropriate value is simply read out. If the instruction expects a vector, then a vector of the expected width is created by replicating the constant value. Bits 4, 5, 6 and 7 are read/write bits but are reserved by many instructions for special purposes. Comparison operators, for example, use these as comparison flag bits. The remaining 64K-8 possible values are read-write bit registers that can be accessed singly or as vectors. This obviously implies that a bit address is 16 bits. Threads also contain 4 numeric ``index'' registers. These are binary values (no unknowns) that can be used in certain cases where extra numeric parameters are needed. The thread instruction set includex %ix/* instructions to manipulate these registers. The instructions that use these registers document which register is used, and what the numeric value is used for. For example, %assign/m uses index register 3 to select the memory bit to target its bit. /* * 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 */