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Operational Description (Continued)

3.3.2.5

CommandPtr

Software initializes CommandPtr.descriptorAddress to con-

tain the address of the first descriptor block that the

CS4210 accesses when software enables the context by

setting ContextControl.run. Software also initializes Com-

mandPtr.Z to indicate the number of descriptors in the first

descriptor block. Software only writes to this register when

both ContextControl.run and ContextControl.active are

zero. The CS4210’s behavior when this rule is violated is

undefined. Since the CS4210 utilizes the CommandPtr reg-

ister while processing a context, there is a set of guidelines

by which software may safely and deterministically read

CommandPtr. These guidelines are based on the Context-

Control bits as listed in Table 3-8 (X = don’t care).

If ContextControl.run is set and ContextControl.dead is not

set, then the contents of CommandPtr are only specified if

both ContextControl.active and ContextControl.wake are

clear. In this instance, CommandPtr.descriptorAddress

contains the address of a descriptor within the last descrip-

tor block that was executed. If ContextControl.run and Con-

textControl.dead are both set, then descriptorAddress

points to a descriptor within the descriptor block in which

an unrecoverable error occurred. Except for the case

where software initializes CommandPtr, the value of Com-

mandPtr.Z is undefined and Z may contain a value that is

implementation dependent. The value of CommandPtr is

undefined after a hardware or software reset of the

CS4210. When software sets ContextControl.run to 1 and

CommandPtr.Z contains an invalid value for the controller

and context, or if a Z value is invalid for a fetched descriptor

block in a running context, the CS4210: sets ContextCon-

trol.dead

and

sets

ContextControl.event

evt_unknown and will not process any descriptors in that

context.

Table 3-8. CommandPtr Read Values

ContextControl Bits

CommandPtr.descriptor Address Value

run

dead

active

wake

A descriptor block address. Either last written or last executed.

Contents unspecified.

1000

Refers to the descriptor block that contains the Z = 0 that caused the

CS4210 to set active to 0.

1001

Contents unspecified.

1010

Contents unspecified.

1011

Contents unspecified.

Points to the descriptor block in which a fatal error occurred.

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