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Xilinx UG129 manual No Operation NOP, 18Loading a Register with Itself Acts as a NOP Instruction

Models: UG129

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Processing Data

R

;Divide Routine (8-bit / 8-bit = 8-bit result, remainder)

;==================================================

;Shift and subtract algorithm

;
div_8by8:
NAMEREG s0, dividend						;	preserved
NAMEREG s1, divisor						;	preserved
NAMEREG s2, quotient						;	preserved
NAMEREG s3, remainder						;	modified
NAMEREG s4, bit_mask						;	used to test bits in dividend,
						;	one-hot encoded, modified
;
LOAD remainder, 00						;	clear remainder
LOAD bit_mask, 80						;	start with most-significant bit (msb)
div_loop:
TEST dividend, bit_mask						;	test bit, set CARRY if bit is '1'
SLA remainder						;	shift CARRY into lsb of remainder
SL0 quotient						;	shift quotient left (multiply by 2)
;
COMPARE remainder, divisor ;							is remainder > divisor?
JUMP C, no_sub						; if divisor is greater, continue to next bit
SUB remainder, divisor						;	if remainder > divisor, then subtract
ADD quotient, 01						;	add one to quotient
no_sub:
SR0 bit_mask						;	shift to examine next bit position
JUMP NZ, div_loop						;	if bit_mask=0, then all bits examined
						;	otherwise, examine next bit
RETURN

	Figure 3-17:8-bit Divided by 8-bit Routine

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No Operation (NOP)

The PicoBlaze instruction set does not have a specific NOP instruction. Typically, a NOP instruction is completely benign, does not affect register contents or flags, and performs no operation other than requiring an instruction cycle to execute. A NOP instruction is therefore sometimes useful to balance code trees for more predictable execution timing.

There are a few possible implementations of an equivalent NOP operation, as shown in Figure 3-18and Figure 3-19. Loading a register with itself does not affect the register value or the status flags.

nop:

LOAD sX, sX

Figure 3-18:Loading a Register with Itself Acts as a NOP Instruction

PicoBlaze 8-bit Embedded Microcontroller

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UG129 (v1.1.2) June 24, 2008

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Xilinx UG129 manual No Operation NOP, 18Loading a Register with Itself Acts as a NOP Instruction

Contents

UG129 v1.1.2 June 24 PicoBlaze 8-bit Embedded Microcontroller User GuideVersion Revision Revision HistoryTechnical Support Limitations Limited Warranty and DisclaimerLimitations Limitation of LiabilityPreface Acknowledgments AcknowledgmentsAbout This Guide Guide ContentsPreface About This Guide Table of Contents Interrupts Performance Appendix C PicoBlaze Instruction Set and Event Reference Introduction PicoBlaze Microcontroller FeaturesIntroduction PicoBlaze Microcontroller Functional BlocksGeneral-Purpose Registers Instruction Program StoreInput/Output Arithmetic Logic Unit ALUFlags Byte Scratchpad RAMCALL/RETURN Stack ResetProgram Counter PC Program Flow ControlWhy Use a Microcontroller within an FPGA? Why the PicoBlaze Microcontroller?Why the PicoBlaze Microcontroller? Weaknesses StrengthsPicoBlaze Interface Signal Descriptions PicoBlaze Interface SignalsSignal Direction Description Readstrobe 1PicoBlaze Instruction Set alphabetical listing PicoBlaze Instruction SetEnable Interrupt Returni Disable Address Spaces Instruction 1Kx18 Direct Logic Instructions Processing DataPicoBlaze Instruction Set 3Inverting an Individual Bit Location 2Complementing a Register ValueArithmetic Instructions 616-Setting a Bit LocationSUB and Subcy Subtract Instructions 10Incrementing and Decrementing a Register Multiplication148-bit by 8-bit Multiply Routine Produces a 16-bit Product Division 168-bit by 8-bit Multiply Routine Using Hardware Multiplier18Loading a Register with Itself Acts as a NOP Instruction No Operation NOPTest and Compare Setting and Clearing Carry Flag22The Test Instruction Affects the Zero Flag Shift and Rotate Instructions 25Generate Parity for a Register Using the Test Instruction5PicoBlaze Rotate Instructions Rotate Left Rotate Right SRXProgram Flow Control Moving Data6Instruction Conditional Execution Description Program Flow ControlCALL/RETURN Program Flow Control UG129 v1.1.2 June 24 1Simple Interrupt Logic Interrupts2Example Interrupt Flow Example Interrupt FlowExample Interrupt Flow 3Interrupt Timing DiagramInterrupts Indirect Addressing Scratchpad RAMAddress Modes Direct AddressingScratchpad RAM Implementing a Look-Up TableFifo Operations Stack OperationsStack Operations Scratchpad RAM Portid Port Input and Output Ports1INPUT Operation and Fpga Interface Logic Input OperationsRegister s0 Input OperationsPORTID70 INPORT70Readstrobe Interaction with FIFOs Applications with Few Input SourcesInput and Output Ports Output Operations Output OperationsFpga Register Simple Output Structure for Few Output Destinations8Use Constant Directives to Declare Output Port Addresses 9Pipelining the Portid Decoding Improves Performance Pipelining for Maximum PerformancePipelining for Maximum Performance Effective Pipelining Improves Read Performance Repartitioning the Design for Maximum PerformanceStandard Configuration Single 1Kx18 Block RAM Instruction Storage ConfigurationsTwo PicoBlaze Microcontrollers Share a 1Kx18 Code Image Instruction Storage ConfigurationsDistributed ROM Instead of Block RAM 6Using Distributed ROM for Instruction MemoryInstruction Storage Configurations Frequency PerformanceInput Clock Frequency Predicting Executing PerformancePerformance Assembler PicoBlaze Development ToolsInput and Output Files Assembly ErrorsPicoBlaze Development Tools Mediatronix pBlazIDE Configuring pBlazIDE for the PicoBlaze Microcontroller4Example of How Kcpsm Source Code Converts to pBlazIDE Code Importing KCPSM3 Code into pBlazIDEFunction KCPSM3 Directive PBlazIDE Directive Differences Between the KCPSM3 Assembler and pBlazIDEDirectives Differences Between the KCPSM3 Assembler and pBlazIDEPicoBlaze Development Tools Vhdl Design Flow Using the PicoBlaze Microcontroller in an Fpga DesignKCPSM3 Module Using the PicoBlaze Microcontroller in an Fpga Design Connecting the Program ROMBlack Box Instantiation of KCPSM3 using KCPSM3.ngc Black Box Instantiation of KCPSM3 using KCPSM3.ngcGenerating the Program ROM using progrom.coe Generating an ESC Schematic SymbolUsing the PicoBlaze Microcontroller in an Fpga Design Locating Code at a Specific Address Assembler DirectivesNaming or Aliasing Registers PBlazIDE Defining ConstantsNaming the Program ROM Output File Defining I/O Ports pBlazIDEOutput Ports Input PortsDefining I/O Ports pBlazIDE 5Example of pBlazIDE Dsout Directive Input/Output PortsCustom Instruction Op-Codes Custom Instruction Op-CodesAssembler Directives Simulating PicoBlaze Code Instruction Set Simulation with pBlazIDE Edit Simulator Control ButtonsInstruction Set Simulation with pBlazIDE 2pBlazIDE Simulator Control Buttons Function AssemblePause RunStep Over Run to CursorTurbocharging Simulation using FPGAs Turbocharging Simulation using FPGAsSimulating PicoBlaze Code Related Materials and References Chapter Related Materials and References KCPSM3 Syntax Example Program TemplatesAppendix Example Program Templates PBlazIDE SyntaxADD sX, Operand -Add Operand to Register sX PicoBlaze Instruction Set and Event ReferenceAppendix PicoBlaze Instruction Set and Event Reference Addcy sX, Operand -Add Operand to Register sX with CarrySX, Operand Logical Bitwise and Register sX with Operand SX, Operand Logical Bitwise and Register sX with OperandExamples Table C-1CALL Instruction Conditions Description ConditionFigure C-4COMPARE Operation Compare sX, Operand Compare Operand with Register sXEnable Interrupt Enable External Interrupt Input Disable Interrupt Disable External Interrupt InputDisable Interrupt Disable External Interrupt Input KCPSM3 Instruction PBlazIDE Instruction Figure C-5FETCH OperationPortid Å Operand SX Å Inport PC Å PC + Interrupt Event, When Enabled Table C-2JUMP Instruction Conditions Description Load sX, Operand Load Register sX with Operand Or sX, Operand Logical Bitwise or Register sX with Operand Or sX, Operand Logical Bitwise or Register sX with OperandFigure C-7OUTPUT Operation and Fpga Interface Logic Reset Event Reset EventTable C-3PicoBlaze Reset Values Resource Reset Event Effect Table C-4RETURN Instruction Conditions Description PBlazIDE Equivalent RET, RET C, RET NC, RET Z, RET NZ Table C-6Rotate Right RR Operation RL sX Rotate Left Register sXRR sX Rotate Right Register sX Table C-5Rotate Left RL OperationSL 0 1 X a sX Shift Left Register sX SL 0 1 X a sX Shift Left Register sXTable C-7Shift Left Operations SR 0 1 X a sX Shift Right Register sX Shift Right with ‘ 0’ fill Figure C-8STORE Operation Store sX, sY SUB sX, Operand -Subtract Operand from Register sXFigure C-10SUBCY Instruction Registers sX Flags CARRY, Zero PBlazIDE Equivalent Subc Figure C-11ZERO Flag Logic for Test Instruction PicoBlaze 8-bit Embedded Microcontroller 117 XOR sX, Operand Logical Bitwise XOR Register sX with Operand Table D-1PicoBlaze Instruction Codes Instruction CodesJump Z PicoBlaze 8-bit Embedded Microcontroller 121 Appendix Instruction Codes Registers Register and Scratchpad RAM Planning WorksheetsReg Description Appendix Register and Scratchpad RAM Planning Worksheets Scratchpad RAMLoc Description