
MOTOROLA
Chapter 7. PCI Bus Interface
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significant 16 lines (AD[31–16]). The special-cycle message encodings are assigned by the
PCI SIG steering committee. The current list of defined encodings and how the MPC106
implements them are provided in Table 7-5.
Note that the power management configuration register (PMCR) controls which special-
cycle messages (if any) the MPC106 broadcasts to the PCI bus. See Section 3.2.4, “Power
Management Configuration Registers (PMCRs),” for a description of the PMCR.
Each receiving agent must determine whether the special-cycle message is applicable to
itself. Assertion of DEVSEL in response to a special-cycle command is not necessary. The
master of the special-cycle transaction can insert wait states but since there is no specific
target, the special-cycle message and optional data field are valid on the first clock IRDY is
asserted. All special-cycle transactions are terminated by master-abort; however, the
received master-abort bit in the master’s status register is not set for special-cycle
terminations.
7.5 Exclusive Access
PCI provides an exclusive access mechanism referred to as a resource lock. The mechanism
locks only the selected PCI resource (typically memory) but allows other nonexclusive
accesses to unlocked targets. In this section, the term ‘locked operation’ means an exclusive
access to a locked target that may span several PCI transactions. A full description of
exclusive access is contained in the
PCI Local Bus Specification
.
The LOCK signal indicates that an exclusive access is underway. The assertion of GNT
does not guarantee control of the LOCK signal. Control of LOCK is obtained in
conjunction with GNT. When using resource lock, agents performing nonexclusive
accesses are free to proceed even while another master retains ownership of LOCK.
7.5.1 Starting an Exclusive Access
To initiate a locked operation, a master must receive GNT when the LOCK signal is not
busy. The master is then said to own the LOCK signal. To request a resource lock, the
master must hold LOCK negated during the address phase of a read command and assert
LOCK in the clock cycle following the address phase. Note that the first transaction of a
locked operation must be a read transaction.
Table 7-5. Special-Cycle Message Encodings
AD[15–0]
Message
Description
0x0000
SHUTDOWN
Indicates the MPC106 is entering the sleep power
saving mode
0x0001
HALT
Indicates the MPC106 is entering either the nap or
sleep power saving mode
0x0002
x86 architecture-specific
This message type is not used by the MPC106.
0x0003–0xFFFF
—
Reserved