68 lines
2.8 KiB
Plaintext
68 lines
2.8 KiB
Plaintext
/*
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* Copyright (c) 2001 Stephen Williams (steve@icarus.com)
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*
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*/
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THREAD DETAILS
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Thread objects in vvp are created by ``.thread'' statements in the
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input source file.
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A thread object includes a program counter and private bit
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registers. The program counter is used to step the processor through
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the code space as it executes instructions. The bit registers each
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hold Verilog-style 4-value bits and are for use by the arithmetic
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operators as they operate.
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The program counter normally increments by one instruction after the
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instruction is fetched. If the instruction is a branching instruction,
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then the execution of the instruction sets a new value for the pc.
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Instructions that use the bit registers have as an operand a <bit>
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value. There is usually space in the instruction for 2 <bit>
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operands. Instructions that work on vectors pull the vector values
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from the bit registers starting with the LSB and up.
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The bit addresses 0, 1, 2 and 3 are special constant bits 0, 1, x and
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z, and are used as read-only immediate values. If the instruction
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takes a single bit operand, then the appropriate value is simply read
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out. If the instruction expects a vector, then a vector of the
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expected width is created by replicating the constant value.
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Bits 4, 5, 6 and 7 are read/write bits but are reserved by many
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instructions for special purposes. Comparison operators, for example,
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use these as comparison flag bits.
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The remaining 64K-8 possible <bit> values are read-write bit registers
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that can be accessed singly or as vectors. This obviously implies that
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a bit address is 16 bits.
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Threads also contain 16 numeric registers. These registers can hold a
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real value or a 64bit integer, and can be used in certain cases where
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numeric values are needed. The thread instruction set includes
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%ix/* instructions to manipulate these registers. The instructions
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that use these registers document which register is used, and what the
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numeric value is used for. Registers 0-3 are often given fixed
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meanings to instructions that need an integer value.
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/*
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* Copyright (c) 2001 Stephen Williams (steve@icarus.com)
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*
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* This source code is free software; you can redistribute it
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* and/or modify it in source code form under the terms of the GNU
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* General Public License as published by the Free Software
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* Foundation; either version 2 of the License, or (at your option)
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* any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
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*/
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