Details

On the C7604 CPU, programming information is sent to the Streaming Engines via SEOPEN, the Streaming Address Generators via SAOPEN, and to the MMA via the HWAOPEN instructions. This programming information is sourced from CUCR registers in the CPU that are populated and updated via the MVC and VPUT family of instructions. Data being written into these CUCR registers can be incorrectly forwarded to the SEOPEN, SAOPEN, and HWAOPEN instructions if in a sequence of three CPU cycles a CUCR register is updated on the first two cycles and then used by an SEOPEN, SAOPEN, or HWAOPEN instruction on the third.

For example, this sequence will cause a forwarding error to occur in the execution of the SAOPEN instruction, corrupting SA0's programming:

MVC .C2 VB0, CUCR0
VPUTD .C2 B1, 0, CUCR0
SAOPEN .C2 CUCR1:CUCR0, 0

Workaround

The issue can be avoided by avoiding the sequence of three execute packets where the first two contain MVC/VPUT instructions that write to the same CUCR and the third contains an SE/SA/HWAOPEN instruction that reads from the same. The workaround is included automatically by the compiler when compiling C7504 code.