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Understanding DLX ISA Floating-Point Instructions: Arithmetic, Conversion, and Comparisons

This document provides an in-depth overview of DLX ISA floating-point instructions, categorized into arithmetic, conversion, and set-on-comparison operations. It details the processes for both single-precision (SP) and double-precision (DP) arithmetic operations, including addition, subtraction, multiplication, and division. Additionally, it explains conversion techniques between different numerical formats and integer types. Special instructions such as TRAP and RFE are also covered, which manage exceptions and interrupts. Lastly, it highlights how comparison operations set floating-point status.

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Understanding DLX ISA Floating-Point Instructions: Arithmetic, Conversion, and Comparisons

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  1. QuadCore Team – DLX ISA • David Bild • Greg Bok • Jake Czyz • Brandon Keao

  2. Floating-Point Instructions • There are three categories for the DLX floating-point instructions: • Arithmetic • Conversion • Set-on-comparison • All operation occur in the floating-point registers and are in the R-type format.

  3. DLX ISA Floating-Point Instructions: Arithmetic Brandon Keao

  4. Floating-Point Instructions: Arithmetic • These intructions preform arithmetic operations on two floating-point registers • Always R-format • There are 2 categories of floating-point arithmetic instructions: • Single-precision • Double-precision

  5. Floating-Point Instructions: Arithmetic • SP operations interpret the values in the two registers as SP FP values • The result is rounded to a SP value and stored in a FP register • ADDF- Adds two SP values • SUBF - Subtracts two SP values • MULTF - Multiplies two SP values • DIVF - Divides two SP values

  6. Floating-Point Instructions: Arithmetic • DP operations interpret the values of two even/odd pairs of FP registers as DP FP values. • The result if rounded to a DP value and stored in an even/odd pair of FP registers. • ADDD - Adds two DP values • SUBD - Subtracts two DP values • MULTD - Multiplies two DP values • DIVD - Divides two DP values

  7. DLX ISA Floating-Point Instructions: Conversion And Special Instructions Greg Bok

  8. Floating-Point Instructions: Conversion • Sometimes need to convert between precisions or integer/floating-point • The DLX ISA includes 6 such instructions • R-format • Double-precision FP register operands must be even-numbered FP registers • 32-bit integers used

  9. Floating-Point Instructions: Conversion • CVT2DF: double-precision to single-precision • CVTD2I: double-precision to integer • CVTF2D: single-precision to double-precision • CVTF2I: single-precision to integer • CVTI2D: integer to double-precision • CVTI2F: integer to single-precision

  10. Special Instructions: TRAP • J-type, unconditional branch • 26-bit name field zero-extended to 32-bits to obtain target address • Moves PC + 8 to IAR (interrupt address register)

  11. Special Instructions: RFE • Return From Exception • J-type, unconditional • Returns to code that was executing before TRAP instruction • Moves value in IAR register to PC

  12. Special Instructions: NOP • R-type • Performs no operation -- hardware state is unaffected • Typically used to fill branch delay slots when no useful instruction will work

  13. DLX ISA Floating-Point Instructions: Set-on-Comparison David Bild

  14. Floating-Point Instructions: Set-On-Comparison • Compares two floating point numbers (SP or DP) • Sets FPSR (Floating Point Status Register) to ‘1’ if comparison is true, ‘0’ if false • 6 comparisons are provided: <, >, =. <=, >=, ~=

  15. DLX ISA Load & Store Instructions Jake Czyz

  16. Load and Store Instructions • For loading/storing data from/to memory • Handle data of size: • Byte • Halfword • Word • Double (for floating point only)

  17. Load and Store Instructions • Byte and Halfword instructions always load/store the least significant byte or halfword, respectively. • Loads and Stores may be done with any of the general purpose registers, except that loading R0 has no effect (it always stores the value 0x00000000).

  18. Load and Store Instructions • All are I-Type • Data always moved between memory and the register(s) specified by rd

  19. Load and Store Instructions • Load/Store Address Calculations: • Load • lw rd rs1 imm • rd = Mem(Sign_Extend(imm) + rs1) • Store • sw rd rs1 imm • Mem(Sign_Extend(imm) + rs1) = rd

  20. Load Instructions • LB Loads a byte (w/ sign ext.) • LBU Loads a byte (w/ zero ext.) • LH Loads a halfword (w/ sign ext.) • LHU Loads a halfword (w/ zero ext.) • LW Loads a word • LF Loads a single precision float • LD Loads a double precision float* *to/from a pair of even/odd registers

  21. Store Instructions • SB Stores a byte • SH Stores a halfword • SW Stores a word • SF Stores a single precision float • SD Stores a double precision float* *to/from a pair of even/odd registers

  22. Thank You

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