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+# Instruction Set Reference
+
+This chapter describes the instruction set for the Vertex-32 and Vertex-64
+architectures in V32 and V64 modes of operation. For each instruction, each
+operand combination is described, a description of the effect upon the FLG
+register and a summary of possible exceptions are also provided.
+
+## Registers
+
+Figure 3.1 shows the initial state of the registers in the ISA. For V32, the
+16 registers are each 32 bits wide. Register `0X` is hardwired with all bits
+equal to 0. General purpose registers `AX` to `GX` hold values that various
+instructions interpret as a collection of Boolean values, or as two's
+complement signed binary integers or unsigned binary integers. The registers
+`PTR`, `IDTR` and `CRX` are considered privileged and writing to them in the
+unprivileged state will generate a general protection fault.
+
+## Base Instruction Formats
+
+In the core V32 ISA, there are four instruction formats (C/I/R/J), as shown in
+Figure 3.3. All are a fixed 32 bits in length and must be aligned on a four-byte
+boundary in memory. An instruction alignment exception is generated if a branch
+or jump instruction is called on an address that is not four-byte aligned. No
+exception is generated on a branch or jump not taken.
+
+## Integer Instructions
+
+Most integer computational instructions operate on 32 or 64 bit values held in
+a register or memory location. Integer instructions are encoded as
+register-immediate operations using the I-type format or as register-register
+operations using the R-type format. The destination is `RD` for both
+register-immediate and register-register operations. If any of the following
+instructions cause an overflow or underflow, the overflow flag is set.
+
+### Integer-Register Instructions
+
+The instructions that follow are operations between registers; an attempt to use
+a non-register operand will result in an invalid opcode exception. The format
+for these exceptions follow Figure 3.4.
+
+#### ADD
+
+`ADD` adds the second and third operands and stores the result in the first
+operand.
+
+#### SUB
+
+`SUB` subtracts the third operand from the second operand and stores the result
+in the first operand.
+
+#### MUL/MULU
+
+`MUL` multiplies the second operand by the third operand and stores the result
+in the first operand. `MULU` performs the same operation on unsigned integers.
+
+#### DIV/DIVU
+
+`DIV` divides the second operand by the third operand. The dividend is stored in
+the upper 16 bits of the first operand, and the remainder is stored in the lower
+16 bits. `DIVU` performs the same operation on unsigned integers.
+
+#### XOR
+
+`XOR` performs a bitwise 'exclusive or' operation between the second and third
+operands and stores the result in the first operand.
+
+#### OR
+
+`OR` performs a bitwise 'or' operation between the second and third operands and
+stores the result in the first operand.
+
+#### AND
+
+`AND` performs a bitwise 'and' operation between the second and third operands
+and stores the result in the first operand.
+
+#### LSL
+
+`LSL` performs a logical shift left. The second operand is shifted left by `n`
+bits, where `n` is the third operand. The result is stored in the first operand.
+
+#### LSR
+
+`LSR` performs a logical shift right. The second operand is shifted right by
+'n' bits, where 'n' is the third operand. The result is stored in the first
+operand.
+
+#### ASR
+
+`ASR` performs an arithmetic shift right. The second operand is shifted right by
+'n' bits, where 'n' is the third operand. The result is stored in the first
+operand.