Requirements
14-4
ADSP-BF535 Blackfin Processor Hardware Reference
Data Flow and Traffic Scheduling
Data flows between the USB host and the attached devices in units of
packets, which are normally 8, 16, 32 or 64 bytes. An exception is the iso-
chronous data type, where packets can be as large as 1023 bytes. The
packets are grouped into larger units called transfers.
To allocate the serial bus bandwidth fairly across all of the attached USB
devices and endpoints, the USB host implements a traffic scheduling algo-
rithm. From the point of view of a USB device, this algorithm is not
deterministic. Although the specific scheduling algorithm is standardized,
the bus dynamically reallocates bandwidth based on factors such as packet
error conditions and flow control. So far as the device is concerned, it can
receive transfer requests for any endpoint at any time.
Depending on the bus loading, the USB host may request packets
back-to-back, or it may request packet transfers to each endpoint in a
round-robin fashion. The USB protocol also allows for detection and
retransmission of packets in cases of bit errors and flow control problems.
Each USB device implementation must maintain state information for
each endpoint that allows large data transfers to occur a packet at a time.
Each device must also maintain state information for each packet to be
retransmitted.
USB Implementation
The ADSP-BF535 processor’s USBD implementation includes:
• The peripheral has a single interrupt output (
USBD_INTR
).
• System software is responsible for managing interrupt priority and
requeueing low priority events as software interrupts.
• Memory access for the USB endpoints is by means of the DAB as a
bus master.
Содержание ADSP-BF535 Blackfin
Страница 80: ...Development Tools 1 26 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 312: ...Working With Memory 6 86 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 332: ...System Interfaces 7 20 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 360: ...Dynamic Power Management Controller 8 28 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 446: ...Beginning and Ending an SPI Transfer 10 40 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 522: ...Timing Examples 11 76 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 562: ...IrDA Support 12 40 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 608: ...PCI I O Issues 13 46 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 672: ...References 14 64 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 810: ...SDRAM Controller SDC 18 86 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 811: ...ADSP BF535 Blackfin Processor Hardware Reference 18 87 External Bus Interface Unit...
Страница 812: ...SDRAM Controller SDC 18 88 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 860: ...DMA Bus Debug Registers 20 30 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 908: ...SDRAM Controller External Bus Interface Unit B 36 ADSP BF535 Blackfin Processor Hardware Reference...