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Toshiba TX39 user manual Data Formats and Addressing, Big endian and little endian formats

Models: TX39

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Architecture

2.4 Data Formats and Addressing

This section explains how data is organized in R3900 registers and memory.

The R3900 uses the following data formats: 64-bit doubleword, 32-bit word, 16-bit halfword and 8-bit byte. The byte order can be set to either big endian or little endian.

Figure 2-5 shows how bytes are ordered in words, and how words are ordered in multiple words, for both the big-endian and little-endian formats.

Higher address	31	23	16 15		8 7		Word address
Higher address
	24				0
	8	9		10		11	8
	4	5		6		7	4
Lower address	0	1		2		3	0

Higher address

Lower address

Byte 0 is the most significant byte (bit 31-24).

A word is addressed beginning with the most significant byte.

(a)Big endian

31	23	15	7	Word address
24	16	8	0
11	10	9	8	8
7	6	5	4	4
3	2	1	0	0

Byte 0 is the least significant byte (bit 7-0).

A word is addressed beginning with the least significant byte.

(b)Little endian

Figure 2-5. Big endian and little endian formats

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Toshiba TX39 user manual Data Formats and Addressing, Big endian and little endian formats

Contents

TX39 Family Core Architecture Page Toshiba Contents EPC Exception Program Counter register Memory location of exception vectorsAppendix a Instruction Set Details Coprocessor Unusable exceptionBus Interface Unit Bus Controller / Write Buffer 227 Bus request and bus grant 227 Cache snoop 228229 230Architecture Architecture Features IntroductionHigh-performance Risc techniques Low power consumption Signal notation Notation Used in This ManualMathematical notation Data notationArchitecture Architecture OverviewRegisters CPU registersCP0 registers Reserved † Exception program counterInstruction Set Overview Operation code 6 bitsSource register 5 bits Destination register 5 bitsLoad/store ComputationalJump/branch CoprocessorComputational Instructions ALU ImmediateALU 3-operand, register type Multiply/Divide Jump/Branch InstructionsCoprocessor Instructions Special InstructionsSpecial Instruction CP0 instructions Instruction Description CP0 InstructionsData Formats and Addressing Big endian and little endian formatsArchitecture Byte addresses of a misaligned word Pipeline Processing Overview User mode Kernel modeMemory Management Unit MMU 1 R3900 Processor Core operating modesDirect segment mapping KusegKseg0 Kseg1Address mapping Architecture Instruction Set Overview Instruction FormatsInstruction Notation Byte specifications for load and store instructions Load and Store InstructionsBase Offset Sync Computational Instructions NOR SLLV, SRLV, Srav Instruction Format and Description MFHI, Mflo Instruction Format and Description MTHI, Mtlo Instruction Format and DescriptionArchitecture Jump/Branch Instructions Jump instructionsInstruction Format and Description Instruction in the delay slot is executed during the jump 10. Branch instructionsArchitecture Special Instructions 11. Special instructionsCoprocessor Instructions COPz Instruction Format and DescriptionBCzT, BCzF Instruction Format and Description Architecture Restore From System Control Coprocessor CP0 Instructions13. System control coprocessor CP0 instructions Cache Instruction Format and DescriptionPipeline Architecture Delay Slot Delayed loadDelayed branching Nonblocking Load Function Nonblocking load functionDivide Instruction DIV, Divu StreamingMemory Management Unit MMU R3900 Processor Core Operating ModesDirect Segment Mapping Internal MMU virtual address spaceKuseg 512MB Exception Processing Utlb TLBL2 Exception Processing Registers Cause registerStatus register Cache registerCause register register no.13 Bits Mnemonic Field name DescriptionRead/Write ExcCode field Mnemonic CauseStatus register register no.12 BitsField name Description ReadStatus register 1/2 Bits Mnemonic Field name Description Value on Read KUc/KUp/KUo Kernel/User mode current/previous/old IEc/IEp/IEo Interrupt Enable current/previous/oldNmI Non-maskable Interrupt IntMask Interrupt MaskCache register register no.7 Cache registerDALc/DALp/DALo Data Cache Auto-Lock current/previous/old IAL DAL Shows how the RFE instruction works BadVAddr Bad Virtual Address register register no.8 PRId Processor Revision Identifier register register no.15Config Configuration register register no.3 21-1910. Config register2/2 Exception Details Address Error exception ∙ Causes ∙ Exception mask∙ Applicable instructions ∙ ProcessingBreakpoint exception ∙ Cause ∙ ServicingBus Error exception ∙ Causes Architecture Coprocessor Unusable exception ∙ Cause Interrupts ∙ Cause Overflow exception ∙ Cause Reserved Instruction exception ∙ CauseReset exception ∙ Cause System Call exception ∙ Cause Non-maskable interrupt ∙ CauseArchitecture Priority of Exceptions Return from Exception HandlerPriority of Exceptions Exception Mnemonic Architecture Caches Instruction CacheData cache configuration Data CacheLock bit setting Lock functionOperation during lock Lock bit clearing Auto-lock bitsCache Test Function Cache disablingCache flushing ExampleCache Refill Cache refillCache Snoop Architecture Debugging Functions System Control Processor CP0 RegistersPRId Processor revision ID Debug †† Debug exception control Depc ††DBD Debug Branch Delay DM Debug Mode 0 at resetDebug register register no.16 BsF Bus Error Exception Flag SSt Single at resetNIS Non-maskable Interrupt Status OES Other Exceptions StatusDebug Exceptions DSS bitTypes of debug exceptions Debug Single Step DSSBranching to a debug exception handler Ii Debug exception handler executionIii Return from a debug exception handler Executing a Deret instructionException priorities Details of Debug Exceptions Single Step exception ∙ Cause∙ Exception masking ∙ Instruction causing this exception Debug Breakpoint exception ∙ CauseArchitecture Appendix a Instruction Set Details Instruction Classes Instruction Formats Instruction Notation Conventions Twos complement division Bitwise logical XOR operationExamples of Instruction Notation Table A-2. Common Load/Store Functions Function MeaningWord access 32 bits Triplebyte access 24 bitsHalfword access 16 bits Byte access 8 bitsJump and Branch Instructions ADD Addi Addiu Addu Rd, rs, rt Andi BCzF Operation Code Bit Encoding BCzFL 111 BCzT 113 BCzTL 115 BEQ Beql Bgez Bgezal Bgezall Bgezl Bgtz Bgtzl Blez Blezl Bltz Bltzal Bltzall Bltzl BNE Bnel Break Bit# Cache Name DataBit# Cache Operation Description Name CFCz COPz COPzCTCz Deret DIV Divu Jump JAL Jalr JR rs LB rt, offsetbase LBU LH rt, offsetbase LHU LUI LW rt, offsetbase LWL 152 LWR 154 Multiply/Add Maddu MFC0 MFCz MFCzMFCz Mfhi Mflo MTC0 MTCz MTCzMthi Mtlo Mult Multu NOR Or rd, rs, rt ORI RFE SB rt, offsetbase Sdbbp SH rt, offsetbase SLL Sllv SLT Slti Sltiu Sltu SRA Srav SRL Srlv SUB Subu SW rt, offsetbase SWL 189 SWR 191 Sync Syscall XOR Xori OPcode Special functionCOPz rs COPz rt CP0 FunctionNotation TMPR3901F 200 R3900 Processor Core On-chip peripheral circuitsBus interface for ease of system implementation Low power consumption, optimal for portable applications Debugging support functions on chipMaximum operating frequency PackageInternal Blocks R3900 Processor Core Clock generatorBus interface unit bus controller / write buffer Address protection unit204 Configuration R3900 Processor CoreInstruction Iimitations Clock Generator Address mappingSync NOP Address Protection Unit Registers Break Address register BAddr0-1Break Mask register BMsk0-1 Break Control register BCnt0-1Break Status register BSts Memory protection exceptionDebug Support Unit SynchronizerRegister address map BSts 0xFF00 BAddr0 Bcnt0 BMsk0 BAddr1 Bcnt1 BMsk1INT* signal synchronization INT50NMI* signal synchronization CPCOND* signal synchronization CPCOND31Pins Enables internal PLL clock Mode quadruple frequency of crystal oscillatorHalt signal. Indicates that TMPR3901F is in halt mode Doze signal. Indicates that TMPR3901F is in doze modeOperations Clock∙ Master Clock ∙ Processor ClockMaster clock Processor System clockClock Read Operation Single ReadBus error during a single read operation Burst Read Burst read 4 words 1 wait Bus error in burst read operation 4 words Write Operation Single write operation 2 waitsInterrupts 1 NMI2 INT50 InterruptBus Arbitration Bus request and bus grantBUSGNT*L Reset Half-Speed Bus Mode Single read operation in half-speed bus modePower-Down Mode Halt mode232 Standby Mode Standby mode PLL stopDoze Mode Reduced Frequency Mode