Lantronix DSTni-EX manual 1. Buffer Descriptor Table, Rx vs. Tx as a Target Device or Host

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Figure 4-1. Buffer Descriptor Table

Figure 4-1. Buffer Descriptor Table

The microprocessor manages buffers intelligently for the USB by updating the BDT as necessary. This allows the USB to handle data transmission and reception efficiently while the microprocessor performs communication-overhead processing and other function-dependent applications. Because the microprocessor and the USB share buffers, DSTni uses a simple semaphore mechanism to distinguish who is allowed to update the BDT and buffers in system memory.

The semaphore bit, also known as the OWN bit, is set to 0 when the microprocessor owns the BD entry. The microprocessor has read and write access to the BD entry and the buffer in system memory when the OWN bit is 0.

When the OWN bit is set to 1, the USB owns the BD entry and the buffer in system memory. The USB has full read and write access and the microprocessor should not modify the BD or its corresponding data buffer. The BD also contains indirect address pointers to where the actual buffer resides in system memory.

Rx vs. Tx as a Target Device or Host

The USB core can function as either a USB target device (function) or a USB host, and can switch operating modes between host and target device under software control. In either mode, the USB core uses the same data paths and buffer descriptors for transmitting and receiving data. Consequently, in this section and the rest of this chapter, the following terms are used to describe the direction of the data transfer between the USB and the USB device.

Rx (or receive) describes transfers that move data from the USB to memory. Tx (or transmit) describes transfers that move data from memory to the USB.

Table 4-1shows how the data direction corresponds to the USB token type in host and target device applications

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Contents Section Five DSTni-EX User GuidePage Lantronix Copyright & TrademarkTechnical Support Master DistributorWarranty 1 About This User Guide Contents2 SPI Controller 3 I2C Controller5 CAN Controllers List of TablesTable 3-17. Clock Control Register List of Figures 1 About This User Guide Conventions Intended AudienceNavigating Online Notes Notes are information requiring attentionOrganization Theory of Operation 2 SPI ControllerSPI Background DSTni SPI ControllerTable 2-1. SPI Controller Register Summary SPI Controller Register SummarySPIDATA Register SPI Controller Register DefinitionsRESET Table 2-2. SPIDATA RegisterInterrupt Request Enable CTL RegisterPhase Select Wire-OTable 2-6. SPISTAT Register SPISTAT RegisterTable 2-7. SPISTAT Register Definitions Interrupt RequestTable 2-10. BCNT Bit Settings SPISSEL RegisterSelectO Signal Table 2-8. SPISSEL RegisterDVDCNTRHI DVDCNTRLO RegisterTable 2-11. DVDCNTRLO Register Table 2-12. DVDCNTRLO Register Definitions3 I2C Controller FeaturesFigure 3-1. DSTni I2C Controller Block Diagram Block DiagramI2C Background Master Transmit Mode I2C ControllerOperating Modes Code Table 3-1. Master Transmit Status CodesI2C State Microprocessor ResponseTable 3-2. Codes After Servicing Interrupts Master Transmit Servicing the InterruptTable 3-3. Status Codes After Each Data Byte Transmits Transmitting Each Data ByteAll Bytes Transmit Completely Master Receive ModeTable 3-4. Master Receive Status Codes Table 3-5. Codes After Servicing Interrupt Master Receive Slave Transmit Mode Receiving Each Data ByteTable 3-6. Codes After Receiving Each Data Byte Slave Receive Mode Bus Clock Speed Bus Clock ConsiderationsClock Synchronization Bus ArbitrationI2C Controller Register Summary Programmer’s ReferenceResetting the I2C Controller Table 3-7. I 2C Controller Register SummarySlave Address Register I2C Controller Register DefinitionsGeneral Call Address Enable Table 3-8. Slave Address RegisterTable 3-10. Data Register Data RegisterTable 3-12. Control Register Control RegisterTable 3-13. Control Register Definitions Extended Slave AddressTable 3-14. Status Register Status RegisterStatus Code Table 3-15. Status Register DefinitionsTable 3-16. Status Codes Table 3-18. Clock Control Register Definitions Clock Control RegisterTable 3-17. Clock Control Register Extended Slave Address Register Software Reset RegisterTable 3-21. Software Reset Register Table 3-22. Software Reset Register Definitions4 USB Controller USB Interrupt USB BackgroundUSB Core Serial Interface EngineDigital Phase Lock Loop Logic USB Hardware/Software InterfaceMicroprocessor Interface Buffer Descriptor TableRx vs. Tx as a Target Device or Host Figure 4-1. Buffer Descriptor TableAddressing BDT Entries Table 4-1. USB Data DirectionTable 4-2. 16-Bit USB Address Table 4-3. 16-Bit USB Address DefinitionsUSB Controller Determines… Table 4-4. BDT Data Used by USB Controller and MicroprocessorMicroprocessor Determines… Table 4-5. USB Buffer Descriptor FormatBD Owner Table 4-6. USB Buffer Descriptor Format DefinitionsDATA0/1 Transmit or Receive USB OwnershipFigure 4-2. USB Token Transaction USB TransactionDedicated to host mode USB Register SummaryTable 4-7. USB Register Summary Interrupt Status Register USB Register DefinitionsTable 4-8. Interrupt Status Register Table 4-9. 16- Interrupt Status Register DefinitionsSleep Timer Enable/Disable USBRST InterruptError Condition USB ResetTable 4-11. 16- Error Interrupt Status Register Definitions Error RegisterTable 4-10. Error Interrupt Status Register Data Field Received Not 8 Bits Error interrupt with two functionsCRC16 Failure PID check field failedLive USB Single Ended Zero Signal Live USB Differential Receiver JSTATE SignalTable 4-12. Status Register Table 4-13. Status Register DefinitionsHost Mode Enable valid for host mode only USB Reset SignalResume Signaling BDT PDD ResetTable 4-15. 16- Address Register Definitions Address RegisterTable 4-14. Address Register Table 4-16. Frame Number Register Frame Number RegistersTable 4-17. Frame Number Register Definitions Frame NumberToken Register Table 4-18. Token Register Endpoint for Token CommandTable 4-19. Token Register Definitions Table 4-20. Valid PID TokensEndpoint Enable Endpoint Control RegistersTable 4-21. Endpoint Control Registers Table 4-22. Endpoint Control Register DefinitionsTable 4-23. Endpoint Control Register Definitions Host Mode OperationFigure 3. Enable Host Mode and Configure a Target Device Sample Host Mode OperationsFigure 4. Full-Speed Bulk Data Transfers to a Target Device Figure 4-5. Pull-up/Pull-down USB USB Pull-up/Pull-down ResistorsUSB Output Enable USB Interface SignalsHOST Mode Enable Clock CLK5 CAN Controllers Data Exchanges and Communication Arbitration and Error CheckingCANBUS Background Table 5-1. Bit Rates for Different Cable Lengths CANBUS Speed and LengthRegister Summary CAN Register SummariesHex Offset RegisterRegister Table 5-4. Detailed CAN Register Map Detailed CAN Register MapHex Offset Acceptance Filter Enable RegisterRegister TX Message Registers CAN Register DefinitionsFigure 5-1. TX Message Routing Sending a MessageTable 5-5. TxMessage0ID28 Tx Message RegistersTable 5-6. TxMessage0ID12 Table 5-7. TxMessage0DataTable 5-13. TxMessage0 Register Definitions Table 5-12. TxMessage0Ctrl FlagsMessage Identifier for Both Standard and Extended Messages Message DataFigure 5-2. RX Message Routing RX Message RegistersTable 5-14. RxMessageID28 Rx Message RegistersTable 5-15. Rx Message ID28 Register Definitions Table 5-16. RxMessageID12Table 5-21. Rx Message Data 39 Register Definitions Table 5-20. Rx Message DataTable 5-22. Rx Message Data Table 5-23. Rx Message Data 23 Register DefinitionsTable 5-27. Rx Message RTR Register Definitions Table 5-26. RxMessage RTRTable 5-28. Rx Message Msg Flags Table 5-29. Rx Message Msg Flags Register DefinitionsTable 5-30. Tx/Rx Error Count Error Count and Status RegistersTable 5-31. Tx\Rx Error Count Register Definitions Table 5-32. Error StatusTable 5-35. Tx/Rx Message Level Register Definitions Table 5-34. Tx/Rx Message Level Registerrxlevel10 txlevel10Note The reset value of this register’s bits is indeterminate Interrupt FlagsCRC Error Format ErrorTable 5-38. Interrupt Enable Registers Interrupt Enable RegistersTable 5-39. Interrupt Enable Register Definitions Bus Off State − int2n group error interruptsTable 5-40. Interrupt Enable Registers CAN Operating ModeTable 5-41. Interrupt Enable Register Definitions Overload Condition − int3n group diagnostic interruptsConfiguration Bit Rate CAN Configuration RegistersFigure 5-3. CAN Operating Mode Table 5-42. Bit Rate Divisor RegisterTable 5-45. Configuration Register Definitions Table 5-44. Configuration RegisterOverwrite Last Message Cfgsjwtseg1 + Bit Timetseg2 + time quanta TQTable 5-46. Acceptance Filter Enable Register Acceptance Filter and Acceptance Code MaskTable 5-47. Acceptance Filter Enable Register Definitions Table 5-48. Acceptance Mask 0 RegisterTable 5-51. Acceptance Mask Register ID12 Definitions Table 5-50. Acceptance Mask Register IDTable 5-52. Acceptance Mask Register Data D5556Table 5-55. Acceptance Code Register Definitions Table 5-54. Acceptance Code RegisterTable 5-56. Acceptance Mask Register ID12 Table 5-57. Acceptance Mask Register ID12 DefinitionsArbitration Lost Capture Register CANbus AnalysisTable 5-60. Arbitration Lost Capture Register Table 5-61. Arbitration Lost Capture Register DefinitionsTable 5-62. Error Capture Register Error Capture RegisterTable 5-63. Error Capture Register Definitions ErrorcodeFrame Reference Register Table 5-65. Error Capture Register DefinitionsTable 5-64. Frame Reference Register Stuff Bit InsertedInterface Connections CAN Bus InterfaceFigure 5-6. CAN Connector Figure 5-5. CAN Bus Interface+5CAN Figure 5-7. Power for CANGNDCAN +24V0.01uf Figure 5-8. CAN Transceiver and Isolation Circuits