ST92163 datasheet(139/224 Pages) STMICROELECTRONICS

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ST92163 - USB PERIPHERAL (USB)

USB INTERFACE (Cont’d)

Bit 0 = Reserved. This bit is fixed by hardware at 0.

INTERRUPT STATUS REGISTER (USBISTR)

R249 - Read/Write

Reset Value: 0000 0000 (00h)

Each bit is set by hardware when the related event

occurs.

If one of these bits is set, the hardware clears the

CTRO bit and sets the V[3:0] bits in the USBIVR

to the interrupt vector containing the address of

the service routine related to these interrupt sourc-

es. If several bits are set only a single interrupt will

be generated.

Note: to avoid spurious clearing of some bits, it is

recommended to clear them with a load instruction

where all bits which must not be altered are set to

1, and all bits to be cleared are set to 0. Read-

modify-write instructions like AND, XOR,... are to

be avoided: consider the case of clearing bit 0 of

USBISTR with an AND instruction, when only bit 7

of USBISTR is at 1 and the others at 0. First the

microcontroller reads the content of USBISTR

(=10h), then it clears bit 7 and writes the result

(=00h) in USBISTR. If between the read and the

write operations another bit were set by hardware

(e.g. bit 5), writing 00h would clear it before the mi-

croprocessor has the time to service the event.

Table 24. Classification of Interrupt Sources:

Bit 7 = Reserved. This bit is fixed by hardware at 0.

Bit 6 = DOVR:

DMA over/underrun.

ST9 processor has not been able to answer a

DMA request in time and the USB FIFO buffer is

full or empty depending on the transfer direction

(reception or transmission).

The USB handles this event in the following way:

during reception the ACK handshake packet is not

sent, during transmission a bit-stuffing error is

forced on the transmitted stream. In both cases

the host will retry the transaction. The DOVR inter-

rupt should never occur during normal operations.

Bit 5 = ERR:

Error.

One of the errors listed below has occurred:

– NANS: No answer. The timeout for a host re-

sponse has expired.

– CRC: CRC error. One of the received CRCs, ei-

ther in the token or in the data, was wrong.

– BST: Bit Stuffing error. A bit stuffing error was

detected anywhere in the PID, data, and/or CRC.

– FVIO: Framing format violation. A nonstandard

frame was received (EOP not in the right place,

wrong token sequence, etc.).

– BUFOVR: Buffer overrun. A packet longer than

the allocated DMA buffer has been received.

DOVR

ERR

ESUSP

SUSP

RESET

SOF

ESOF

Interrupt

Class

DOVR

DMA Over/Underrun event

ERR

Notification event

ESUSP

Notification event

SUSP

Notification event

RESET

Notification event

SOF

Notification event

ESOF

Notification event

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