USB Programming Model
14-60
ADSP-BF535 Blackfin Processor Hardware Reference
Exception Handling
Software must handle several exception cases. These exceptions consist of
catastrophic endpoint errors, isochronous packets with data errors, and
failed memory access requests.
Small Packets (Less Than 16-Byte Transfers)
The DMA master channel is required to address data in minimum bursts
of 16 bytes.For this reason, using the USBD module with packet sizes of
less than 16 bytes presents a challenge to system software.
To use 16-byte or smaller packets, the USB module pads the data to main-
tain the 16-byte boundary. It is up to the system software to read the
USBD_EPLENx
register to determine the valid data.
Endpoint Errors
Under normal circumstances, the hardware handles transfer errors on
individual data packets transparently without software intervention. The
USB protocol supports packet retries for Bulk, Control, and Interrupt
packets.
In cases where a catastrophic problem occurs on a specific endpoint, and
the device needs support from the application software (such as a configu-
ration change), the device has the option to stall individual endpoints.
When a device stalls an endpoint, the USB host is required to clear the
stall condition before further data transfers can occur on the endpoint.
Presumably, while clearing the stall condition, the application also fixes
the underlying condition which caused the stall in the first place.
The USBD module includes a stall bit for each endpoint in the
USBD_CTRL
register. When software needs to indicate a stall condition, it sets the
USBD_EPxSTALL
bit. After the
USBD_EPxSTALL
bit has been set, application
behavior is product specific. The application must clear the
USBD_EPxSTALL
bit in the
USBD_CTRL
register.
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...