DP83266 datasheet(103/152 Pages) NSC

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70 Control Information (Continued)

Bit

Symbol

Description

EXCR0

Exception on RCHN0

This bit is set by the MACSI device when an exception occurs on RCHN0 An

exception condition consists of one of the following events ABus Error Consistency Failure (REQ or ODUD)

BMAC MAC Reset Timeout (TRT expires) BMAC abort (MAC frame received or FCRequest Class

inconsistency) RINGOP change host abort (via SAR register) FIFO underrun or confirmation exception (for

full Confirmation) No action is taken by the MACSI device if the host sets this bit

This bit indicates that a request on RCHN0 did not complete normally This implies that an exception event

occurred or that the Request is improperly formed The corresponding Confirmation (CNF) Descriptor will give

more status about the failure The additional information in the CNF descriptor should be used to make a

decision about the severity of the error If the exception was caused by an ABus error the RQSTOP will also

be set

RCMR0

Request Complete on RCHN0

Is set by the MACSI device when it has completed processing a Request

object on RCHN0 This completion may be a normal completion where a request object was transmitted

without error It may also be an abnormal completion due to one of the exception conditions listed above in

EXCR0 This bit (together with the Breakpoint bit BRKR0) indicates that there are CNF descriptors to be

processed No action is taken if the Host sets this bit

USRR0

Unserviceable Request on RCHN0

This bit is set by the MACSI device when a Request cannot be

processed on RCHN0 This occurs when the Request Class is inappropriate for the current ring state (eg

Asynchronous transmission while RINGOP e 0) or when there is no CNF status space or when the host

aborts a request by clearing the ABR bit in the Service Attention Register While this bit is set no requests will

be processed on RCHN0

The host must clear this bit to resume request processing If the USRR0 was set due to lack of CNF space this

condition must be corrected by giving the MACSI device more CNF space before restarting the channel If it

was due to a request classRINGOP incompatibility then the reason for the incompatibility must be resolved

103

DP83266 Datasheet(PDF) 103 Page - National Semiconductor (TI)