Intel B940 Datasheet download pdf (Page 15)

Datasheet, Volume 2 15

Processor Configuration Registers

2 Processor Configuration

Registers

2.1 Register Terminology

Table 2-1 shows the register-related terminology that is used in this chapter.

Table 2-1. Register Terminology (Sheet 1 of 2)

Item Description

RO Read Only bit(s). Writes to these bits have no effect. These are static values only.

RO-V

Read Only/Volatile bit(s). Writes to these bits have no effect. These are status bits only. The

value to be read may change based on internal events.

RO-V-S

Read Only/Volatile/Sticky bit(s). Writes to these bits have no effect. These are status bits

only. The value to be read may change based on internal events. Bits are not returned to their

Reset Values by “warm” reset, but is reset with a cold/complete reset (for PCI Express* related

bits a cold reset is “Power Good Reset” as defined in the PCI Express Base Specification).

Atomic Flag bit(s). The first time the bit is read with an enabled byte, it returns the value 0, but

a side-effect of the read is that the value changes to 1. Any subsequent reads with enabled bytes

return a 1 until a 1 is written to the bit. When the bit is read, but the byte is not enabled, the

state of the bit does not change, and the value returned is irrelevant, but will match the state of

the bit.

When a 0 is written to the bit, there is no effect. When a 1 is written to the bit, its value becomes

0, until the next byte-enabled read. When the bit is written, but the byte is not enabled, there is

no effect.

Conceptually, this is “Read to Set, Write 1 to Clear”

Read/Write bit(s). These bits can be read and written by software. Hardware may only change

the state of this bit by reset.

RW1C

Read/Write 1 to Clear bit(s). These bits can be read. Internal events may set this bit. A

software write of 1 clears (sets to 0) the corresponding bit(s) and a write of 0 has no effect.

RW1C-L-S

Read/Write 1 to Clear/Lockable/Sticky bit(s). These bits can be read. Internal events may

set this bit. A software write of 1 clears (sets to 0) the corresponding bit(s) and a write of 0 has

no effect. Bits are not cleared by “warm” reset, but is reset with a cold/complete reset (for PCI

Express related bits a cold reset is “Power Good Reset” as defined in the PCI Express Base spec).

Additionally there is a Key bit (which is marked RW-K or RW-L-K) that, when set, prohibits this bit

field from being writable (bit field becomes Read Only/Volatile).

RW1C-S

Read/Write 1 to Clear/Sticky bit(s). These bits can be read. Internal events may set this bit.

A software write of 1 clears (sets to 0) the corresponding bit(s) and a write of 0 has no effect.

Bits are not cleared by "warm" reset, but is reset with a cold/complete reset (for PCI Express

related bits a cold reset is “Power Good Reset” as defined in the PCI Express Base spec).

RW-K

Read/Write/Key bit(s). These bits can be read and written by software. Additionally this bit,

when set, prohibits some other target bit field from being writable (bit fields become Read Only).

RW-L

Read/Write/Lockable bit(s). These bits can be read and written by software. Additionally

there is a Key bit (which is marked RW-K or RW-L-K) that, when set, prohibits this bit field from

being writable (bit field becomes Read Only).

RW-L-K

Read/Write/Lockable/Key bit(s). These bits can be read and written by software. This bit,

when set, prohibits some other bit field(s) from being writable (bit fields become Read Only).

Additionally there is a Key bit (which is marked RW-K or RW-L-K) that, when set, prohibits this bit

field from being writable (bit field becomes Read Only).

Conceptually, this may be a cascaded lock, or it may be self-locking when in its non-default state.

When self-locking, it differs from RW-O in that writing back the Reset Value will not set the lock.

RW-V

Write/Volatile bit(s). These bits can be read and written by software. Hardware may set or

clear the bit based on internal events, possibly sooner than any subsequent software read could

retrieve the value written.

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Intel B940 Datasheet Page 15

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