Specifications

Product Errata 87
Revision Guide for AMD Athlon™ 64 and AMD Opteron™ Processors
25759 Rev. 3.79 July 2009
153 Potential System Hang in Multiprocessor Systems With ≥14
Cores
Description
Under a highly specific and detailed set of internal timing conditions the crossbar flow control buffer
pointer can become corrupted, causing incorrect information to be captured and resulting in a system
hang.
Potential Effect on System
The system hangs.
Suggested Workaround
A BIOS workaround can be implemented to modify the buffer allocation scheme to limit the
maximum number of crossbar command buffers to 49, with some performance impact. The AMD
recommended buffer allocation for ladder and twisted ladder configurations are listed in the tables
below. This requires modifications to the configuration registers Dev:0x90h, B0h, D0h, Dev:3x70h,
and Dev:3x78h (command buffers only) and assumes default values in Dev:3x7Ch.
Outer Node Virtual Channel Command Buffer Allocation
Total Command Buffer Allocation Per Outer Node
Link Request Posted Request Response Probe
Number of
Command Buffers
Coherent links 1 1 6 4 12
Non-coherent links 5 4 1 0 10
SRI 2 3 3 0 8
MCT 0 0 5 2 7
Allocation Outer Node
12 Coherent link
12 Coherent link
10 Non-coherent link
8 SRI (includes three buffers from FreeList Buffer Count
register)
7MCT
49 Total