ADSP-BF535 Blackfin Processor Hardware Reference
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USB Device
The
USBD_PC
interrupt can be used by software to monitor the
progress of a transfer on a packet-by-packet basis. The
USBD_BCSTAT
interrupt indicates when the byte count for the transfer has
expired, and a new buffer must be set up. The
USBD_TC
interrupt
indicates a completed transfer.
5. For multiple block transfers, repeat steps 1 through 4 until all
blocks have been transferred.
If a bulk IN data transfer ends on a packet boundary, an additional
block with a size of 0 bytes must be created to terminate the
transfer.
Due to packet scheduling on the USB, resetting the endpoint regis-
ters between transfers is a time-critical operation to avoid
generating NAKs on the USB.
Bulk Transfers
Bulk data transfers (as well as interrupt and control transfers) are based
around a limited set of packet sizes. The USB 1.1 specification defines
valid sizes of 8, 16, 32, and 64 bytes. Each USB endpoint is assigned one
of these possible basic packet sizes and cannot switch between them.
All large data transfers are broken down into units of the basic packet
sizes. For example, a 1044-byte file transfer across the USB to a 64-byte
bulk endpoint consists of 17 packet transfers. The first 16 packets are 64
bytes, and the remaining 20 bytes are carried in a short packet. The USB
host automatically assumes that the short packet represents an
end-of-transfer indicator.
Scheduling individual packet transfers on the USB is non-deterministic
from the device’s standpoint. It does not know in advance when the host
is going to make a request. The best the device can do to ensure maximum
bandwidth use of the USB is to be ready for a transfer at all times. This
means setting up multiple buffering for the endpoints.
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...