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+# SPARC V9 ISA Reference
+
+Reference documentation for the SPARC V9 instruction set as implemented in ReviveSparc.
+
+## Overview
+
+The SPARC V9 architecture is a 64-bit RISC ISA developed by Sun Microsystems and standardized by SPARC International. ReviveSparc implements the full SPARC V9 specification, including the VIS (Visual Instruction Set) extensions.
+
+### Key Features
+
+- 64-bit integer and floating-point registers
+- 32 general-purpose registers (register windowed)
+- 32 floating-point registers (quad-precision capable)
+- Delayed branching with annulment
+- Register windowing with 8 global + up to 32 windowed registers
+- Precise exceptions and multiple trap levels
+
+## Instruction Set Categories
+
+### Integer Instructions
+
+```
+ADD      Add                  ADDcc    Add and modify CC
+AND      And                  ANDcc    And and modify CC
+OR       Or                   ORcc     Or and modify CC
+XOR      Exclusive Or         XORcc    Exclusive Or and modify CC
+SUB      Subtract             SUBcc    Subtract and modify CC
+MULX     Multiply Extended    UDIVX    Unsigned Divide Extended
+SDIVX    Signed Divide Extended
+SLL      Shift Left Logical   SRL      Shift Right Logical
+SRA      Shift Right Arithmetic
+```
+
+### Load/Store Instructions
+
+```
+LDUB     Load Unsigned Byte
+LDSB     Load Signed Byte
+LDUH     Load Unsigned Halfword
+LDSH     Load Signed Halfword
+LDW      Load Word
+LDX      Load Doubleword
+STB      Store Byte
+STH      Store Halfword
+STW      Store Word
+STX      Store Doubleword
+LDF      Load Floating-point
+LDDF     Load Double Floating-point
+STF      Store Floating-point
+STDF     Store Double Floating-point
+```
+
+### Branch Instructions
+
+```
+Bcc      Branch on Condition
+BPcc     Branch on Condition (Predicted)
+BPr      Branch on Register
+CALL     Call and Link
+RETT     Return from Trap
+JMPL     Jump and Link
+RETURN   Return from Subroutine
+```
+
+### Floating-Point Instructions
+
+```
+FADDs    FP Add (single)
+FADDd    FP Add (double)
+FSUBs    FP Subtract (single)
+FSUBd    FP Subtract (double)
+FMULs    FP Multiply (single)
+FMULd    FP Multiply (double)
+FDIVs    FP Divide (single)
+FDIVd    FP Divide (double)
+FSQRTs   FP Square Root (single)
+FSQRTd   FP Square Root (double)
+F CMPs   FP Compare (single)
+F CMPd   FP Compare (double)
+```
+
+### VIS Instructions
+
+```
+FPACK16  Pack 16-bit
+FPACK32  Pack 32-bit
+FALIGNDATA  Align Data
+FEXPAND  Expand
+FMUL8x16  Multiply 8-bit by 16-bit
+FMUL8x16AU  Multiply 8-bit by 16-bit (unsigned)
+FMUL8x16AL  Multiply 8-bit by 16-bit (unsigned)
+FMUL8SUx16  Multiply 8-bit Signed by 16-bit Unsigned
+FMUL8ULx16  Multiply 8-bit Unsigned by 16-bit Unsigned
+FMULD8SUx16  Multiply Double 8-bit Signed by 16-bit Unsigned
+FMULD8ULx16  Multiply Double 8-bit Unsigned by 16-bit Unsigned
+```
+
+## Register Windows
+
+SPARC V9 uses register windows to optimize function call performance:
+
+- **8 global registers** (%g0 through %g7, where %g0 is always zero)
+- **Up to 32 register windows**, each containing 16 registers
+- Each window provides: 8 incoming (%i0-%i7), 8 local (%l0-%l7), 8 outgoing (%o0-%o7) — with overlap between adjacent windows
+- The number of windows is implementation-dependent
+
+## Privileged Registers
+
+| Register | Description |
+|----------|-------------|
+| TPC      | Trap PC (1-4) |
+| TNPC     | Trap Next PC (1-4) |
+| TSTATE   | Trap State (1-4) |
+| TT       | Trap Type (1-4) |
+| TBA      | Trap Base Address |
+| PSTATE   | Processor State |
+| TL       | Trap Level |
+| PIL      | Processor Interrupt Level |
+| CWP      | Current Window Pointer |
+| CANSAVE  | Cleanable Windows |
+| CANRESTORE | Restorable Windows |
+
+## Trap Types
+
+| TT Value | Trap Name | Description |
+|----------|-----------|-------------|
+| 0x01     | instruction_access_exception | Memory access fault |
+| 0x03     | instruction_access_error | Hardware error |
+| 0x04     | illegal_instruction | Unimplemented instruction |
+| 0x05     | privileged_operation | Trap in user mode |
+| 0x06     | fp_disabled | FPU not enabled |
+| 0x08     | clean_window | Register window spill needed |
+| 0x09     | division_by_zero | Integer divide by zero |
+| 0x20-0x2f | interrupt_vector | External interrupts |
+| 0x60-0x7f | software_trap | `ta` instruction traps |
+| 0x80     | data_access_exception | Data memory access fault |
+| 0x82     | data_access_error | Data memory hardware error |