Applications with Few Input Sources | Xilinx UG129 specification

R

Chapter 6: Input and Output Ports

IN_D

IN_C

IN_B

IN_A

Registering the multiplexer output is

1 1 allowed because PORT_ID is asserted for two clock cycles. Registering improves performance.

1 0

PicoBlaze Microcontroller

	IN_PORT[7:0]	OUT_PORT[7:0]
	0 1	PORT_ID[7:0]
	0 1	READ_STROBE
		READ_STROBE
		WRITE_STROBE
	0 0
	S0
	S1
	PORT_ID[0]
	PORT_ID[1]
		UG129_c6_03_060404

Figure 6-3:Multiplex Multiple Input Sources to Form a Single IN_PORT Port

Failure to include a register anywhere in the path from PORT_ID to IN_PORT is the most common reason for decreased system clock rates. Consequently, make sure that this path is registered at some point.

Applications with Few Input Sources

If the application has 32 or less input ports, then a single multiplexer is ideal to connect the various input signals to the IN_PORT input port, as shown in Figure 6-3. Check the results of synthesis to ensure that the special MUXF5, MUXF6, MUXF7, and MUXF8 are being employed to make the most efficient multiplexer structure.

Refer to UG331 Chapter 8: Using Dedicated Multiplexers (see Reference 5).

READ_STROBE Interaction with FIFOs

Occasionally, the circuit providing data to the PicoBlaze microcontroller needs to know that it was successfully read. Figure 6-4shows an example using a FIFO buffer. The FIFO only updates its read pointer once the PicoBlaze microcontroller successfully captures data, indicated by the READ_STROBE signal.

52	www.xilinx.com	PicoBlaze 8-bit Embedded Microcontroller
		UG129 (v1.1.2) June 24, 2008

Image 52

Xilinx UG129 manual Applications with Few Input Sources, Readstrobe Interaction with FIFOs, Input and Output Ports

Contents

PicoBlaze 8-bit Embedded Microcontroller User Guide UG129 v1.1.2 June 24 Revision History Version Revision Limited Warranty and Disclaimer LimitationsLimitation of Liability Technical Support Limitations Acknowledgments Preface Acknowledgments Guide Contents About This Guide Preface About This Guide Table of Contents Interrupts Performance Appendix C PicoBlaze Instruction Set and Event Reference PicoBlaze Microcontroller Features Introduction PicoBlaze Microcontroller Functional Blocks General-Purpose RegistersInstruction Program Store Introduction Arithmetic Logic Unit ALU FlagsByte Scratchpad RAM Input/Output Reset Program Counter PCProgram Flow Control CALL/RETURN Stack Why Use a Microcontroller within an FPGA? Why the PicoBlaze Microcontroller?Why the PicoBlaze Microcontroller? Strengths Weaknesses PicoBlaze Interface Signal Descriptions PicoBlaze Interface SignalsSignal Direction Description Readstrobe PicoBlaze Instruction Set 1PicoBlaze Instruction Set alphabetical listing Enable Interrupt Returni Disable Address Spaces Instruction 1Kx18 Direct Logic Instructions Processing DataPicoBlaze Instruction Set 2Complementing a Register Value 3Inverting an Individual Bit Location 616-Setting a Bit Location Arithmetic Instructions SUB and Subcy Subtract Instructions Multiplication 10Incrementing and Decrementing a Register 148-bit by 8-bit Multiply Routine Produces a 16-bit Product 168-bit by 8-bit Multiply Routine Using Hardware Multiplier Division No Operation NOP 18Loading a Register with Itself Acts as a NOP Instruction Setting and Clearing Carry Flag Test and Compare 22The Test Instruction Affects the Zero Flag 25Generate Parity for a Register Using the Test Instruction Shift and Rotate Instructions SRX 5PicoBlaze Rotate Instructions Rotate Left Rotate Right Moving Data Program Flow Control Program Flow Control 6Instruction Conditional Execution Description CALL/RETURN Program Flow Control UG129 v1.1.2 June 24 Interrupts 1Simple Interrupt Logic Example Interrupt Flow 2Example Interrupt Flow 3Interrupt Timing Diagram Example Interrupt Flow Interrupts Scratchpad RAM Address ModesDirect Addressing Indirect Addressing Implementing a Look-Up Table Scratchpad RAM Fifo Operations Stack OperationsStack Operations Scratchpad RAM Input and Output Ports Portid Port Input Operations 1INPUT Operation and Fpga Interface Logic Input Operations PORTID70INPORT70 Register s0 Readstrobe Interaction with FIFOs Applications with Few Input SourcesInput and Output Ports Output Operations Output Operations Simple Output Structure for Few Output Destinations Fpga Register 8Use Constant Directives to Declare Output Port Addresses Pipelining for Maximum Performance 9Pipelining the Portid Decoding Improves Performance Pipelining for Maximum Performance Repartitioning the Design for Maximum Performance Effective Pipelining Improves Read Performance Instruction Storage Configurations Standard Configuration Single 1Kx18 Block RAM Instruction Storage Configurations Two PicoBlaze Microcontrollers Share a 1Kx18 Code Image 6Using Distributed ROM for Instruction Memory Distributed ROM Instead of Block RAM Instruction Storage Configurations Performance Input Clock FrequencyPredicting Executing Performance Frequency Performance PicoBlaze Development Tools Assembler Input and Output Files Assembly ErrorsPicoBlaze Development Tools Configuring pBlazIDE for the PicoBlaze Microcontroller Mediatronix pBlazIDE Importing KCPSM3 Code into pBlazIDE 4Example of How Kcpsm Source Code Converts to pBlazIDE Code Differences Between the KCPSM3 Assembler and pBlazIDE DirectivesDifferences Between the KCPSM3 Assembler and pBlazIDE Function KCPSM3 Directive PBlazIDE Directive PicoBlaze Development Tools Vhdl Design Flow Using the PicoBlaze Microcontroller in an Fpga DesignKCPSM3 Module Connecting the Program ROM Using the PicoBlaze Microcontroller in an Fpga Design Black Box Instantiation of KCPSM3 using KCPSM3.ngc Generating the Program ROM using progrom.coeGenerating an ESC Schematic Symbol Black Box Instantiation of KCPSM3 using KCPSM3.ngc Using the PicoBlaze Microcontroller in an Fpga Design Locating Code at a Specific Address Assembler DirectivesNaming or Aliasing Registers Defining Constants Naming the Program ROM Output FileDefining I/O Ports pBlazIDE PBlazIDE Output Ports Input PortsDefining I/O Ports pBlazIDE Input/Output Ports 5Example of pBlazIDE Dsout Directive Custom Instruction Op-Codes Custom Instruction Op-Codes Assembler Directives Simulating PicoBlaze Code Instruction Set Simulation with pBlazIDE Simulator Control Buttons Instruction Set Simulation with pBlazIDE2pBlazIDE Simulator Control Buttons Function Assemble Edit Run Step OverRun to Cursor Pause Turbocharging Simulation using FPGAs Turbocharging Simulation using FPGAs Simulating PicoBlaze Code Related Materials and References Chapter Related Materials and References Example Program Templates KCPSM3 Syntax PBlazIDE Syntax Appendix Example Program Templates PicoBlaze Instruction Set and Event Reference ADD sX, Operand -Add Operand to Register sX Addcy sX, Operand -Add Operand to Register sX with Carry Appendix PicoBlaze Instruction Set and Event Reference SX, Operand Logical Bitwise and Register sX with Operand SX, Operand Logical Bitwise and Register sX with Operand Examples Condition Table C-1CALL Instruction Conditions Description Compare sX, Operand Compare Operand with Register sX Figure C-4COMPARE Operation Enable Interrupt Enable External Interrupt Input Disable Interrupt Disable External Interrupt InputDisable Interrupt Disable External Interrupt Input Figure C-5FETCH Operation KCPSM3 Instruction PBlazIDE Instruction Portid 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 Operand Figure 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 RL sX Rotate Left Register sX RR sX Rotate Right Register sXTable C-5Rotate Left RL Operation Table C-6Rotate Right RR Operation SL 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 SUB sX, Operand -Subtract Operand from Register sX Store sX, sY Figure 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 Instruction Codes Table D-1PicoBlaze Instruction Codes Jump 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