Intel
®
81341 and 81342—Inter-Processor Messaging Unit
Intel
®
81341 and 81342 I/O Processors
Developer’s Manual
December 2007
858
Order Number: 315037-002US
13.6.37 IMU Test and Set Registers — IMUTSR[0:511]
There are five hundred and twelve (512) 8-bit IMU Test and Set Registers (IMUTSRx).
Each 8-bit entry implements 2 bits, one per Intel XScale
®
processor. Bit 0 corresponds
to Intel XScale
®
processor 0 and bit 1 corresponds to Intel XScale
®
processor 1. The
valid values of an IMUTSRx are 00
2
, 01
2
, and 10
2
. An Intel XScale
®
processor can only
read the other Intel XScale
®
processor’s bit. For example, an Intel XScale
®
processor
can only affect the value of its bit by one of the following events:
• A read performed by an Intel XScale
®
processor to an IMUTSRx register when both
bits are cleared will set that particular Intel XScale
®
processor bit in the IMUTSRx.
• A write of 0
2
to an IMUTSRx bit by an Intel XScale
®
processor will only clear its
corresponding bit in the IMUTSRx register.
When an Intel XScale
®
processor reads an IMUTSRx register and both bits are cleared,
the value returned to the Intel XScale
®
processor will be the current value of the bits
(00
2
in this case), followed by the hardware setting that particular Intel XScale
®
processor bit. For example, if Intel XScale
®
processor 1 reads an IMUTSRx register and
both bits are cleared, 00
2
will returned as the value read and the hardware will set bit
1, which will result in bits[1:0] of the IMUTSRx equal to 10
2
.
When an IMUTSRx contains a non-zero value, and any of the Intel XScale
®
processor
reads that particular register, the value of the bits will not be affected and the non-zero
value will be returned to the Intel XScale
®
processor.
Note:
When an Intel XScale
®
processor attempts a write of 1
2
to its bit in an IMUTSRx
register, the bit will not be affected.
Note:
Although the bits’ attributes are defined as Read/Write, writing a 1
2
to a bit does not
have any effect.
Warning:
The IMU Test and Set Registers must be accessed one byte at a time. If multiple bytes
are accessed in one transaction, the result will be unpredictable.