User`s guide

DWMBB Adapter

3.6 Lockout Modes

The DWMBB has four lockout modes. Lockout Assert Enable (bit

<8>) and Lockout Response Enable (bit <7>) (both in the ACSR,

Control and Status Register) determine the lockout mode.

The four DWMBB lockout modes are:

• Mode 0 – The DWMBB ignores the XMI LOCKOUT L signal.

• Mode 1 – The DWMBB responds to the XMI LOCKOUT L signal but

does not assert it.

• Mode 2 – DWMBA Compatibility Mode: The DWMBB asserts the

XMI LOCKOUT L signal but does not respond to its assertion from

another XMI node.

• Mode 3 – Full XMI Lockout (default mode after power-up and XMI

node reset): The DWMBB asserts and responds to the assertion of the

XMI LOCKOUT L signal.

The XMI LOCKOUT L signal is used to prevent lock starvation problems.

When an Interlock Read (IREAD) transaction to a locked memory location

occurs, the XMI memory returns a LOC response.

If the DWMBB receives an IREAD from the VAXBI while XMI LOCKOUT

L is asserted, the IREAD is retried on the VAXBI, enabling a VAXBI node

with a pending Unlock Write transaction to gain access to the XMI to

complete its IREAD–Unlock Write transaction. More than one XMI cycle

is required to retry the IREAD on the VAXBI.

The DWMBB retries on the VAXBI all IREADs that either receive a LOC

response from memory or that are prohibited from being transmitted

on the XMI because of the assertion of XMI LOCKOUT L by another

XMI node. The DWMBB asserts the XMI LOCKOUT L signal when the

number of consecutive IREAD retries equals or exceeds the lockout limit

value. The lockout limit value is speciﬁed by the Lockout Limit ﬁeld of the

Utility Register (AUTLR<31:28>). The default value is 4 (hex).

If the DWMBB reaches its lockout limit but another node has asserted

the XMI LOCKOUT L signal, the DWMBB waits until the other node

deasserts the signal and then it asserts XMI LOCKOUT L.

The DWMBB has a lockout deassertion timer that controls the maximum

time that the XMI LOCKOUT L signal remains asserted. At power-up, the

value of the lockout deassertion timer is 2 to 3 ms.

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