12. Register Descriptions
246
PowerSpan II User Manual
80A1010_MA001_09
Integrated Device Technology
www.idt.com
When an EEPROM is detected by PowerSpan II’s I
2
C Interface after reset, certain registers are
initialized with the contents of the EEPROM. See
for details on which
register fields are loaded through EEPROM.
12.3
Configuration and IACK Cycle Generation
PowerSpan II has registers that must be programmed in order for a PCI master to generate
configuration (Type 1 or 0) and IACK transactions on the alternate PCI Interface and for the processor
bus to generate configuration (Type 1 or 0) and IACK transactions on either PCI bus.
12.3.1
From PCI-to-PCI
The following PowerSpan II registers are used by a PCI master to generate configuration (Type 1 or 0)
and IACK transactions on the alternate PCI Interface:
•
Px_CONF_INFO/Px_CONF_DATA
•
Px_IACK
12.3.1.1
PCI Configuration Data
Generating a Configuration transaction on PCI requires the programming of the
Configuration Cycle Information Register” on page 276
(Px_CONF_INFO) in order set-up the address
of the Configuration cycle. The PCI transaction is generated when a register access occurs on
the
“PCI-1 to PCI-2 Configuration Cycle Data Register” on page 279
(Px_CONF_DATA).
When a register write is performed to Px_CONF_DATA, the address and data parameters in
Px_CONF_DATA are used to generate a configuration transaction on the alternate PCI bus.
When a register read is performed to Px_CONF_DATA, the read is retried while a configuration read
transaction is generated on the alternate PCI bus. The address for the read transaction is defined by
Px_CONF_INFO. While the data is being retrieved, register accesses to Px_CONF_DATA is retried.
The Px_CONF_INFO and Px_CONF_DATA registers must be treated as shared resources for
applications that require more than one agent to generate configuration transactions on PCI. A
semaphore is used to control access.
12.3.1.2
Interrupt Acknowledge Generation
The Px_IACK register is used to generate IACK reads on the alternate PCI bus. If a register read is
performed to Px_IACK, then the read is retried while an IACK cycle is generated on the alternate PCI
bus. The address for the IACK cycle is taken directly from the originating PCI bus.
The Px_IACK register must be treated as shared resources for applications that require more than one
agent to generate IACK transactions on PCI. A semaphore is used to control access.
Writes to Px_IACK have no effect.