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System Controller: Doorbell Registers
10006757-02 PmPPC7448 User’s Manual
5-13
DOORBELL REGISTERS
The MV64460 uses the doorbell registers in the messaging unit (MU) to request interrupts
on both the PCI and CPU buses. There are two types of doorbell registers:
Outbound: These are set by the MV64460’s local CPU to request an interrupt service on the PCI bus.
Inbound: These are set by an external PCI agent to request interrupt service from the local CPU.
Outbound Doorbells
The local CPU generates an interrupt request to the PCI bus by setting bits in the Outbound
Doorbell register (ODR). The interrupt may be masked in the Outbound Interrupt Mask reg-
ister (OIMR), but that does not prevent the bit from being set in the ODR. The ODR is
located at PCI_0 offset 0x1C2C.
Note: The CPU or the PCI interface can set the ODR bits. This allows for passing interrupt requests between CPU and
PCI interfaces.
Inbound Doorbells
The PCI bus generates an interrupt request to the local CPU by setting bits in the Inbound
Doorbell register (IDR). The interrupt may be masked in the Inbound Interrupt Mask regis-
ter (IIMR), but masking the interrupt does not prevent the bit from being set in the IDR. The
IDR is located at PCI_0 offset 0x1C20.
Note: The interrupt request triggered from the PCI bus can be targeted to the CPU or to the PCI interface, depending
on the software setting of the interrupt mask registers.
MONARCH FUNCTIONALITY
The PmPPC7448 can be configured to function as either a Monarch or non-Monarch mod-
ule, as described in the VITA 32 PPMC specification. A Monarch is the main PPMC device on
the local PCI bus. It performs enumeration on that bus after power-up and is often the inter-
rupt handler. A non-Monarch module does not perform enumeration on the local bus after
power-up. Bit 2 of Board Configuration Register 3 (see
Register Map 7-10) at location
F820,C000
16
indicates how the module is configured (0=non-Monarch, 1=Monarch), as
determined by the signal on pin 64 of connector P12. The software can read the Monarch
line status to configure the board, and the hardware is unaffected.
The EReady register (see
Register Map 7-7) at location F820,5000
16
has an additional bit to
support Monarch functionality. EREADY bit 0 monitors the EREADY line. For a non-Mon-
arch, it is presumed that this signal is initially asserted, then removed when the bus is ready
for enumeration. When all the other PCI devices have stopped driving this signal low, the
Monarch will enumerate the bus. Please see the PPMC standard (reference in
Table 1-3) for
carrier board pull-up requirements.