IBM PowerPC 750GX User Manual page 76

User's Manual
IBM PowerPC 750GX and 750GL RISC Microprocessor
User Sampled Instruction Address Register (USIA)
The contents of SIA are reflected to USIA, which can be read by user-level software. USIA can be accessed
with the mfspr instructions using SPR 939.
Sampled Data Address Register (SDA) and User Sampled Data Address Register (USDA)
The 750GX does not implement the Sampled Data Address Register (SDA) or the user-level, read-only
USDA registers. However, for compatibility with processors that do, those registers can be written to by boot
code without causing an exception. SDA is SPR 959; USDA is SPR 943.
Programming Model gx_02.fm.(1.2)
Page 76 of 377 March 27, 2006