12. Register Descriptions
245
PowerSpan II User Manual
80A1010_MA001_09
Integrated Device Technology
www.idt.com
12.1.3
Access from the Processor Bus
The PB_REG_BADDR register specifies the 4-Kbyte aligned base address for PCSR space on the
processor bus. This register is programmed through any register interface or through EEPROM.
Register accesses through the Processor Bus Interface can be big-endian or PowerPC little-endian (see
“Processor Bus and PowerSpan II Register Transfers” on page 179
). The endian conversion for register
accesses from the Processor Bus Interface is controlled with the END bit in the PB_REG_BADDR
Register. The default mode is big-endian.
The reset state for the base address for PCSR space on the processor bus is 0x3000_0000.
12.1.4
Access from Multiple Interfaces
PowerSpan II allows reads to its registers from all of its bus interfaces at the same time. However,
writes may occur from only one bus interface at a time. This prevents data corruption if two or more
interfaces try to write to the same register simultaneously.
PowerSpan II uses an internal round robin arbitration mechanism for register access from the different
bus interfaces. Register writes are retried until the interface doing the write has successfully arbitrated
for register access.
Each PowerSpan II PCI Target has a Px Lockout (Px_LOCKOUT) bit in the
and Status Register” on page 318
(MISC_CSR). While a lockout bit is set, the corresponding PCI
Target retries all Configuration Type 0 transactions. When the Base Address registers have been
configured, memory transactions are claimed, but they are retried until the lockout bit is cleared. By
default the Px_LOCKOUT bits are set. The lockout bits can either be cleared by EEPROM load, or by
an access from the Processor Bus Interface. The lockout bits are automatically cleared by PowerSpan II
when the PWRUP_BOOT bit in the
“Processor Bus Arbiter Control Register” on page 307
PCI.
12.2
Register Reset
The PCSR space is divided into four reset domains:
•
PCI-1 CSR space
•
PCI-2 CSR space
•
Processor Bus Interface registers
•
Device Specific registers
for a detailed description of register reset partitioning.
Register writes to “write 1 to set/clear” status bits may not be reflected by an
immediate register read.
Register accesses from all interfaces are retried during EEPROM load.