Intel
®
81341 and 81342 I/O Processors
December 2007
Developer’s Manual
Order Number: 315037-002US
419
Messaging Unit—Intel
®
81341 and 81342
4.6
Index Registers
The Index Registers are a set of 1004 registers that when written by an external host I/
O interface agent can generate an interrupt to the Intel XScale
®
processor. These
registers are for inbound messages only. The interrupt is recorded in the Inbound
Interrupt Status Register.
The storage for the Index Registers is allocated from the 81341 and 81342 local DDR
memory. Write accesses to the Index Registers write the data to local DDR memory.
Read accesses to the Index Registers read the data from local DDR memory. The local
DDR memory used for the Index Registers ranges from MU Base Address Registers
+50H to the MU Base Address Reg FFFH. The MU Base Address registers
(MUBAR and MUUBAR) must be programmed properly in order to map the MU space
within DDR memory space, and the DDR Memory space must be within the ATU
translation window. The MU Base Address Registers allow the index registers to be
placed in any 8-KByte space of the Host I/O Interface Address Translation window.
The address of the first write access is stored in the Index Address Register. This
register is written during the earliest write access and provides a means to determine
which Index Register was written. Once updated by the MU, the Index Address Register
is not updated until the Index Register Interrupt bit in the Inbound Interrupt Status
Register is cleared. When the interrupt is cleared, the Index Address Register is re-
enabled and stores the address of the next Index Register write access.
Writes by the Intel XScale
®
processor to the local memory used by the Index Registers
does not cause an interrupt and does not update the Index Address Register.
The index registers can be accessed with multi-word transactions.
Warning:
The MU Base Address Register (MUBAR and MUUBAR) must be programmed by
software for proper operation of the MU. Using the MUBAR and MUUBAR, the MU can be
relocated to any address space on the internal bus. However, the MU must be mapped
in the ATU translated address space. In addition, the MU must overlap the DDR
memory address space in order for the Index Registers to be functional.