Entering and exiting an exception software action | Digi NS7520

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Entering and exiting an exception (software action)

The ARM7TDMI performs specific steps when handling exceptions.

Entering an exception

When handling an exception, ARM7TDMI does this:

1Preserves the address of the next instruction in the appropriate Link register.

–If the exception has been entered from the ARM state, the address of the next instruction is copied into the Link register. The address is either current PC + 4 or PC + 8, depending on the exception. (See Table 18: "Exception entry/exit by exception type" on page 38.)

–If the exception has been entered from Thumb state, the value written into the Link register is the current PC offset by a value that lets the program continue from the correct place on return from the exception.

The exception handler does not need to determine from which state the exception was entered. With an SWI, for example, MOVS PC, R14_SVC always returns to the next instruction whether executed in ARM or Thumb state.

2Copies the CPSR into the appropriate SPSR.

3Forces the CPSR mode bits to a value that depends on the exception.

4Forces the PC to fetch the next instruction from the relevant exception vector.

5Sets the I (for IRQ interrupts) or F (for FIRQ interrupts) bits to disable interrupts to prevent unmanageable nesting of exceptions.

Note: If the processor is in Thumb state when an exception occurs, it automatically switches into ARM state when the PC is loaded with the exception vector address.

Exiting an exception

On completion, ARM7TDMI does this:

1Moves the Link register, minus the offset where appropriate, to the PC. The offset value varies depending on the type of exception.

2Copies the SPSR back to the CPSR.

3Clears the interrupt disable flags, if they were set on entry.

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Digi NS7520 manual Entering and exiting an exception software action, Entering an exception, Exiting an exception

Contents

NS7520 Hardware Reference Page Part number/version 90000353D Release date March Page Contents A p t e r 4 B B u s M o d u l e A p t e r 7 M e m o r y C o n t r o l l e r M o d u l e A p t e r A p t e r 1 0 S e r i a l C o n t r o l l e r M o d u l e D e Who should read this guide About this guide What’s in this guide Conventions used in this guideTo read about See For Contact information Documentation updatesRelated documentation Customer supportPage About the NS7520 Key features and operating modes of the major NS7520 modules NS7520 Features O u t t h e N S 7 5 2 7 5 2 0 F e a t u r e s NS7520 overview NS7520 module block diagram Operating frequency Pinout and Packaging NS7520 packaging dimensions Symbol Min Nom MaxPackaging NS7520 pinout and dimensions NS7520 BGA layout Column Description Pinout detail tables and signal descriptions External bus Symbol Pin DescriptionSystem bus interface System bus interface pinout ADDR4 ADDR7ADDR6 ADDR5 Do not USE Signal descriptions System bus interface signal descriptionMnemonic Signal Description Chip select controller Chip select controller pinoutBusy Mnemonic Signal Chip select controller signal description Ethernet interface MAC pinout Ethernet interface MAC Ethernet interface MAC signal description CRS COL General-purpose I/O No connect pinsNo connect pins Serial Other Pin Serial channel Signal Description DSR RTS PORTC4 RXCB/RIB ResetPORTA3 Rxda DACK1 PORTA2 Dsra Amux Serial channel Other Description Gpio signalSerial signal Other signal System clock and reset Clock generation and reset signal descriptionSystem clock pinout Bisten System mode test supportSystem mode and system reset pinout Plltst ARM debugger signal description Jtag test ARM debuggerJtag test pinout Trst termination GND Power supplyPower supply pinout Signal Pin Description Working with the CPU CPU performance ARM Thumb concept ARM ARM modeWorking with ARM exceptions ARM performance Exception priorities Summary of ARM exceptions Exception vector table Exception vector tableVector Description Address Reset exception Detail of ARM exceptionsUndefined exception Abort exception SWI exception Firq exception IRQ exception Entering and exiting an exception software action Entering an exceptionExiting an exception Abort P Reset UndefException entry/exit summary Exception entry/exit by exception type Hardware Interrupts Firq and IRQ linesInterrupt controller Interrupt sources W . d i g i . c o m Page BBus Module Module Master Slave BBus masters and slavesCycles and BBus arbitration BBus masters and slaves Address decoding BBus address decodingAddress range Module Page SYS Module Signal description Signal mnemonic Signal name DescriptionJtag support ARM debug System clock generation NS7520 clock moduleExternal oscillator vs. internal PLL circuit NS7520 clock module block diagram Using the external oscillator External oscillator mode hardware configuration PLL mode hardware configuration Using the PLL circuit PLL mode hardware configuration Bits Access Mnemonic Reset Description D3109 Reserved Setting the PLL frequencyPLL Settings register Setting the PLL frequency on bootup PLL Settings register bit definition PLL multiplier Bits Access Mnemonic Reset DescriptionMHz A87 A65 A40 ND+1 PLL Settings reg Output divider MHz A87 A65 A40 ND+1 PLL Settings reg PLL Control register bit definition PllcntSysclk frequency MHz ND+1 PLL Settings register Reset circuit sources Address bit Name Description NS7520 bootstrap initialization GEN Module Address Register Module configurationGEN module address configuration GEN module hardware initialization General information GEN module registersSystem Control register Address FFB0 Software watchdog timeout in seconds Bclk output disableSoftware watchdog enable Software watchdog reset/interrupt select Bus monitor enable Enable access to internal chip registers in CPUUser mode Bus interface TEA/LAST configuration Bits Access Mnemonic ResetDescription Enable ARM CPU DMA module test mode CPU disable DMA module resetTA input synchronizer NS7520 revision ID Last reset caused by external resetSystem Status register System Status register bit definition Product ID defined by external resistor jumpers Last reset caused by watchdog timerLast reset caused by PLL update Last reset caused by software reset Address FFB0 000C Software Service registerTimer Control registers Software Service register bit definition Timer interrupt mode Timer Control registers bit definitionTimer enable Timer interrupt enable Timer prescaler Timer clock sourceInitial timer count Current timer count Timer Status registersTimer Status registers bit definition Timer interrupt pending Porta data direction Porta Configuration registerPorta mode configuration Porta register bit definition Porta data register Porta ConfigurationPorta configuration Adata IN/SER1DCD PORTA1 Gpio Gpio OUT SER1CTS DONE1OUT PORTA0 SER1SPISENABLEInputs Outputs Portc data direction Portc Configuration registerPortc mode Portc register bit definition Portc data register Portc configurationPortc configuration Cdata PORTC1 Gpio Gpio OUT LEVELIRQ1=CDIR1 PORTC0 LEVELIRQ0=CDIR0 PORTC30 Interrupts Address FFB0 0030 / 0034 Interrupt controller registers Interrupt Enable registers bit definition D01 Page Memory Controller Module About the MEM module Pin configurationMEM module pin configuration by memory type Mode A2714 A130 CSx Mode A2714 A130 SdramRAS CAS Address Mnemonic Register MEM module configurationSetting the chip select address range Memory controller register map Memory Space Refresh count value Memory Module Configuration registerEnable Dram refresh Mmcr bit definition Refresh cycle count Enable external address multiplexingEnable A27 output Rcyc AMUX2 A27 and A26 bit settingsEnable A26 output Enable A25 output Base address Chip Select Base Address registerChip Select Base Address register bit definition Base Dram configuration mode Peripheral page sizeDram address multiplexer select Force Bclk at end of memory cycle External TA configurationDram internal address multiplexer mode Burst memory cycle enable Write-protect the chip select EepromValid bit Mask Address Chip Select Option Register aChip Select Option Register a bit definition Mask When DRSEL=0 When DRSEL=1 and DMODE=2’b00When DRSEL=1 and DMODE=2’b01 at full speed Port size When DRSEL=1 and DMODE=10Burst access size in beats Bsize WE Ctrl Read cycle modeWrite cycle mode OE Ctrl Chip Select Option Register B bit definition Chip Select Option Register B Sync Static memory Sram controller Sync Write Sync Read Single cycle read/write Async Read Burst cycles Using the internal multiplexer NS7520 Dram address multiplexing000 001 010 011 100 101 110 111 7 5 2 0 D R a M a d d r e s s m u l t i p l e x i n g Internal Dram multiplexing Mode NS7520 multiplexed address outputsDram Using the external multiplexer FP/EDO Dram controller Dram refresh FP Dram Write FP Dram Read Normal FP Dram bus cycles FP Dram burst cycles FP/EDO Dram burst cycles X32 Sdram configuration NS7520 Sdram interconnectX32 Sdram interconnect BA1 Bclk CLK VCC CKE X16 Sdram configurationBA1 BA0 Udqm NS7520 signal 16M Sdram signal 64M Sdram signalX16 Sdram interconnect CAS3 RAS CAS2 CAS1 CAS0 Bclk CLK VCC CKE X8 Sdram configurationsNS7520 signal 16M Sdram signal X8 Sdram interconnect Sdram A10/AP support Command Command definitionsSdram command definitions Mux mode X32 X16 Burst length Bsize configurationCAS latency Bcyc configuration Memory timing fields Sdram Address Field Value Sdram Mode registerSdram Mode register settings Full Sdram normal read Sdram read cycles Sdram burst read Sdram normal write Sdram write cycles Sdram burst write Example Peripheral page burst size Wait Bcyc Page DMA Module Fly-by operation transfers DMA module DMA fly-by transfers Memory-to-memory operation DMA buffer descriptor DMA buffer descriptor Fly-by mode Buffer descriptor bit definitions Buffer descriptor bit definitionsBit Description Buffer descriptor field definitions Buffer descriptor field definitionsField Description Channel Base address DMA channel peripheral Fly-by mode DMA channel assignmentsDMA channel assignments DMA channel registers Address mapAddress Description Address Description DMA Control register Buffer Descriptor Pointer register Channel abort request DMA channel enableDMA operation mode DMA Control register bit definition Burst transfer enable Memory-to-memory modeBTE Channel request source REQ Destination address increment SincSource address increment Dinc Data operand size Current DMA channel state shown in binaryCurrent DMA channel buffer descriptor index Normal completion interrupt pending DMA Status/Interrupt Enable registerDMA Status/Interrupt Enable register bit definition Error completion interrupt pending Buffer not ready interrupt enable Premature complete interrupt enableNormal completion interrupt enable Error completion interrupt enable Ethernet transmitter considerations External peripheral DMA support Ethernet receiver considerations Signal Description Signal descriptionExternal DMA configuration Memory-to-memory mode Hardware needed for external memory-to-memory DMA transfers DMA controller resetPage Ethernet Module Fifo Ethernet front-end EFE Transmit and receive FIFOs EFE transmit processingEFE receive processing DMA Receive buffer descriptor selection External CAM filtering MAC module MAC module block diagram Other modules in the diagram include EFE configuration EFE register mapAddress Register Register description Mcfg MaxfSupp Test Erxregetxreg Erfifohetfifoh Erxbretxbc Ethernet General Control register Egcr bit definitionsAddress FF80 Erxetx Erxdmaetxdma Erxlngetxwm Erxshtefulld Erxbad Ethernet General Control register bit definition Receiver in interrupt service mode Enable transmit FifoEnable transmit DMA Do not set this bit when operating the Ethernet Enable full-duplex operation Enable Transmit Data register ready interruptEnable transmit data Fifo half empty interrupt Enable transmit buffer complete interrupt Insert transmit source address MAC software resetInvert the transmit clock input PSOS pNA buffer descriptors Mode field Output based on EFE CSR bit Endec mode and NS7520 pinsEndec control signal cross-reference External interface mode Ethernet General Status register Egsr bit definitions Ethernet General Status register bit definitionRxfdbrxskip Rxregrtxrege Rxfifohtxfifoh Rxbrtxbc Receive buffer ready Receive Fifo data availableReceive register ready Receive Fifo half full Transmit buffer complete Receive buffer skipTransmit register empty Transmit Fifo half empty Writing to the Ethernet Fifo Data register Endec status signal cross-referenceEthernet Fifo Data register Address FF80 0008 / FF80 000C secondary address Reading from the Ethernet Fifo Data register Fifo data FF80 Ethernet Transmit Status registerEthernet Fifo Data register bit definition Ethernet Transmit Status register bit definition Transmit abort late collision Packet transmitted OKBroadcast packet transmitted Multicast packet transmitted Transmit abort excessive collisions TxaedTransmit abort excessive deferral Txaec Transmit abort jumbo TxaurTransmit aborted underrun Txaj Txcrc Transmit CRC errorTxdef Transmit packet deferred Ethernet Receive Status register TxcolcTransmit collision count Receive data violation event previously seen Ethernet Receive Status register bit definitionReceive buffer size in bytes Receive carrier event previously seen Receive multicast packet Receive packet has CRC errorReceive packet has dribble bit error Receive broadcast packet Receive packet has code violation Receive packet is too longReceive packet is too short MAC Configuration Register RoverReceive overflow MAC Configuration Register 1 bit definition Receive enable RX flow controlPass ALL receive frames MAC Configuration Register 2 bit definition CRC enable Auto detect pad enableVlan pad enable PAD/CRC enable PAD operation Pad operation table Back-to-Back Inter-Packet-Gap register Back-to-Back Inter-Packet-Gap register bit definitionBack-to-back inter-packet-gap Non back-to-back inter-packet-gap part Non-Back-to-Back Inter-Packet-Gap registerAddress FF80 040C Non-Back-to-Back Inter-Packet-Gap register bit definition Retransmission maximum Collision Window/Collision Retry registerCollision Window/Collision Retry register bit definition Collision window Maximum Frame register Maximum Frame register bit definitionMaximum frame length PHY Support register bit assignment PHY Support register Address FF80 041C Enable Jabber protectionBit mode Test register Test backpressure Test pauseShortcut pause quanta Clock select MII Management Configuration registerMII Management Configuration register bit definition Reset MII management Clks field Sysclk ratio MHz example Clks field settingsScani Scan increment single scan for read data Single scan for read data MII Management Command registerMII Management Command register bit definition Automatically scan for read data MII PHY register address MII Management Address registerMII Management Address register bit definition MII PHY device address MII write data MII Management Write Data registerAddress FF80 042C MII Management Write Data register bit definition MII Management Read Data register MII Management Read Data register bit definitionMII read data Automatically scan for read data in progress MII Management Indicators registerMII Management Indicators register bit definition Read data not valid Smii Status register Station Address registersSmii Status register bit definition Station address octet Station Address RegisterStation Address Register 1 bit definition Station Address Register 2 bit definition OCTET5 Station Address Register 3 bit definitionOCTET3 OCTET4 Station Address Filter register Address FF80 05C0Station Address Filter register bit definition Address FF80 05D4 Register hash tableMulticast hash table entries and bit definitions Address FF80 05D0 HT3 bit definition Address FF80 05D8Address FF80 05DC HT2 bit definition Calculating hash table entries W . d i g i . c o m Page W . d i g i . c o m Page Serial Controller Module RTS, CTS, DTR, DSR, DCD, RI Supported features Bit-rate generator Serial port block diagram Serial protocols Uart mode SPI mode Terminology What’s being written Value Fifo managementTransmit Fifo interface Operating in Endian modes Receive Fifo interface Processor interrupts vs. DMA Using DMA Using processor interrupts SPI master mode SignalsConfiguration SPI master transmitter SPI master receiver SPI slave mode Signals SPI slave receiver SPI slave transmitter SPI slave mode 0 and 1 two-byte transfer General-purpose I/O configurations Configuration Operating Mode Serial Port Maximum RateSerial port performance N f i g u r a t i o n Serial Channel Control Register a Serial Channel registersSerial Channel 1, 2 Control Register a Address FFD0 0000 Number of stop bits Parity enableStick parity Even parity select General-purpose output 1/General-purpose Enable the transmitter with active CTSRemote loopback Local loopback Receiver interrupt condition Enable receive DMA requestsData terminal ready active Request-to-send active Transmitter interrupt condition Receiver interrupt enable bitsEnable transmit DMA requests Receiver interrupts Transmitter interrupts Transmitter interrupt enable bits Serial Channel 1, 2 Control Register B Address FFD0 0004Serial Channel Control Register B bit definition Bitordr Enable receive character GAP timerSCC mode Rcgt Enable active RTS only while transmitting Transmit encodingReceive data encoding Differential Manchester 111. a 1 is Address FFD0 0008 Serial Channel 1, 2 Status Register a Character Match3 Serial Channel Status Register a bit definitionCharacter Match1 Character Match2 Cgap Buffer GAP timerCharacter GAP timer Bgap Current data set ready state Current ring indicator stateDCD Current data carrier detect state Receive framing error interrupt pending Receive parity error interrupt pendingReceive break interrupt pending Receive overrun interrupt pending RrdyReceive register ready interrupt pending Receive Fifo half-full interrupt pending Receive buffer closed interrupt pendingReceive Fifo full Change in CTS interrupt pending Change in DCD interrupt pendingChange in RI interrupt pending Change in DSR interrupt pending Transmit register empty interrupt pending Transmit Fifo half-empty interrupt pendingTransmit buffer closed interrupt pending Serial Channel 1, 2 Bit-Rate registers Address FFD0 000C / 4CTempty Receive clock source Bit-rate generator enableTiming mode Serial Channel Bit-Rate register bit definition Transmit clock source Drive receive clock externalDrive transmit clock external Clkmux BRG input clockTransmit clock invert Receive clock invert Tdcr If Dpll is not used and you are not usingIf Dpll is not used but you are using When Dpll is used in the application, Receive divide clock rate Rdcr Receiver internal clock source TicsTransmit internal clock source Rics With the 18.432MHz crystal using Xtale as the clock source Max baudrates with different clock sourcesNreg 16X @ 55.296MHz With the 18.432MHz crystal using Sysclk as the clock source Bit rate examples X1 mode X8 mode X16 modeSerial Channel 1, 2 Fifo registers Address FFD0 0010 Data Serial Channel 1, 2 Receive Buffer Gap TimerAddress FFD0 0014 Data Address FFD0 0018 Serial Channel 1, 2 Receive Character Gap TimerRegister diagram and bit assignment Serial Channel Receive Buffer Gap Timer bit definition CT value Serial Channel Receive Character Gap Timer bit definition Address FFD0 0020 Serial Channel 1,2 Receive Match registerSerial Channel 1, 2 Receive Match Mask register Address FFD0 001C / 5C RMMB3 Serial Channel Receive Match Mask register bit definitionRMMB1 RMMB2Page Electrical Characteristics Sym Parameter Conditions Min Typ Max Unit DC characteristicsRecommended operating conditions Recommended operating thermal conditions DC characteristics outputs Input/Output characteristicsPad pullup and pulldown characteristics DC characteristics inputs Internal pullup characteristics Maximum voltage ratings AC characteristicsAC electrical specifications Absolute maximum ratings MDC, MDIO, TXEN, TXER, TXD30 Estimated Signal Load pF Device loadsSystem loading details PORTA3, PORTA1, PORTC3, PORTC1 MDC, TXD30, TXER, TXEN, TDO Oscillator CharacteristicsSignal Derating ns/pF Output buffer derating by load capacitance NS7520 TimingSpecifications Timing Diagrams Resettiming Reset timing parametersNum Description Min Typ Max Units Sram timing Sram timing parametersNum Description Min Max Unit CS* controlled read wait = Sram read Sram burst read CS* controlled read wait = 0, Bcyc = CS controlled write internal and external, wait = Sram write Sram burst write OE* controlled read wait = Sram OE read Sram OE burst read WE* controlled write wait = Sram WE write Sram WE burst write Sdram timing parameters Sdram timing Sdram read, CAS latency = Sdram read Active Read Inhibit Prechg Bterm Sdram burst read Sdram burst read Sdram write Sdram write Sdram burst write Sdram burst write Sdram refresh Sdram load mode FP Dram timing parameters FP Dram timing Fast Page read FP Dram read Fast Page burst read FP Dram burst read Fast Page write FP Dram write Fast Page burst write FP Dram burst write Fast page refresh Rcyc = Fprefreshcycles CAS3 CAS2 CAS1 CAS0 RF1 RF2 RF3 RF4 RF5 RF8 Ethernet timing parameters Ethernet timing Ethernet cam timing Ethernet PHY timing Num Description Min Max Units Jtag arm ice timing diagramJtag timing Jtag arm ice timing parameters Jtag bscan timing parameters Jtag bscan timing diagram External DMA timing parameters External DMA timing Fly-by external DMA Memory-to-memory external DMA 2T SYS Serial internal timing characteristicsSerial external timing characteristics Serial internal/external timing Synchronous serial external clock Synchronous serial internal clock Gpio timing diagram Gpio timingGpio timing parameters Page Index CPU Non-Back-to-BackInter-Packet-Gap register FP Dram Portc NET+ARM PORTC0 Receiver interrupts 229 transmitter interrupts Undefined exception 32 Page