ADSP-BF535 Blackfin Processor Hardware Reference
14-53
USB Device
Isochronous Transfers
Isochronous endpoints are guaranteed exactly one packet transfer per USB
frame. The maximum size of the packet is specified in the endpoint’s
descriptors (software), and in the EpBufs (hardware). In any given frame,
the USB may transfer from 0 to the maximum number of bytes allocated
for the endpoint.
The specific timing of the packet within a frame is dynamic based on the
USB traffic load. In the worst-case scenario, a device can get an isochro-
nous packet request at the end of frame X, and then another immediately
at the beginning of frame X+1. For this reason, isochronous applications
should consider prebuffering an entire packet one frame in advance of
when it is needed.
For USB IN endpoints, prebuffering an entire packet involves setting up
the transfer for the next frame as soon as the
USBD_TC
interrupt is received
for the current frame. For USB OUT endpoints, this translates to putting
a buffer in place as soon as the
USBD_TC
interrupt is received for the cur-
rent frame.
For USB OUT endpoints, the device software should program the byte
count to the exact size of the maximum packet for the endpoint (1 to
1023 bytes). For USB IN transfers, the device software should program
the byte count to match the amount of data to be transferred in a given
frame (the maximum packet size or less).
If the USB device does not have any data to transfer on a particular frame,
it should disarm the endpoint by clearing the
USBD_ARM
bit in the
USBD_EPCFGx
register.
To monitor the progress of transfers, the device software monitors the
USBD_SOF
interrupt, and it can look at the status fields of the
USBD_STAT
register to see exactly what is occurring on the bus at any given time.
Specific examples of ISO IN and ISO OUT register programming are
shown in the following sections.
Summary of Contents for ADSP-BF535 Blackfin
Page 80: ...Development Tools 1 26 ADSP BF535 Blackfin Processor Hardware Reference...
Page 312: ...Working With Memory 6 86 ADSP BF535 Blackfin Processor Hardware Reference...
Page 332: ...System Interfaces 7 20 ADSP BF535 Blackfin Processor Hardware Reference...
Page 360: ...Dynamic Power Management Controller 8 28 ADSP BF535 Blackfin Processor Hardware Reference...
Page 446: ...Beginning and Ending an SPI Transfer 10 40 ADSP BF535 Blackfin Processor Hardware Reference...
Page 522: ...Timing Examples 11 76 ADSP BF535 Blackfin Processor Hardware Reference...
Page 562: ...IrDA Support 12 40 ADSP BF535 Blackfin Processor Hardware Reference...
Page 608: ...PCI I O Issues 13 46 ADSP BF535 Blackfin Processor Hardware Reference...
Page 672: ...References 14 64 ADSP BF535 Blackfin Processor Hardware Reference...
Page 810: ...SDRAM Controller SDC 18 86 ADSP BF535 Blackfin Processor Hardware Reference...
Page 811: ...ADSP BF535 Blackfin Processor Hardware Reference 18 87 External Bus Interface Unit...
Page 812: ...SDRAM Controller SDC 18 88 ADSP BF535 Blackfin Processor Hardware Reference...
Page 860: ...DMA Bus Debug Registers 20 30 ADSP BF535 Blackfin Processor Hardware Reference...