Intel 82558 Manuale Utente

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Note: The SCB Status word is not updated immediately in response to SCB commands. For example, the 

CU status will remain in the idle state for a period of time after the CU start command is issued. 
Software should not rely exclusively on the state of the SCB Status word to determine when it is 

appropriate to issue commands requiring the device to be in a specific state. Software may be 

required to keep an internal state engine on the commands recently issued to the device to insure 
that data read from the register is valid.

The SCB Command word is also addressable as two bytes. The upper byte is called the Interrupt 

Control byte. The least significant byte is called the Command byte.

The Interrupt Control byte allows software to either force the generation of an interrupt or mask 
device interrupts from occurring. The 82558 and later devices also allow individual interrupt 

sources from within the device to be masked (this feature is not available in the 82557).

Bits 7:6

CUS

This field contains the CU status (2 bits). Valid values are for this field are:

00    Idle
01    Suspended
10    LPQ Active
11    HQP Active

Bits 5:2

RUS

This field contains the RU status (4 bits). Valid values are:

0000    Idle
0001    Suspended
0010    No resources
0011    Reserved
0100    Ready
0101    Reserved
0110    Reserved
0111    Reserved
1000    Reserved
1001    Reserved
1010    Reserved
1011    Reserved
1100    Reserved
1101    Reserved
1110    Reserved
1111    Reserved

Bits 1:0

Reserved

These bits are reserved and should not be used.

Specific Interrupt Mask Bits

SI

M

CU Command

0

RU Command