Processor Base Frequency Xeon 6338N

[ct73]

Hi, I am trying to determine the processor base frequency using the method described in 20.7.3 of:

Intel® 64 and IA-32 Architectures
Software Developer’s Manual

Order Number: 325462-080US
June 2023

The basic method is to poll the CPUID.15H register and read the EAX, EBX, and ECX values from it. There is a caveat that if ECX is zero, which it is when I read it, then the value should be determined from table 20-91. But that table doesn't have an entry for my processor. I have a Xeon 6338N with a CPU ID signature of 6_6A. The table only has a value for Xeon Scalable Processors with CPUID signature 6_55.

Does anyone know how to handle this?

Thanks!

[Thomas_W_Intel]

Is your problem to implement an automated detection algorithm or is your main concern to know the base frequency of your processor? 
For the latter, it would be simpler to look it up: https://ark.intel.com/content/www/us/en/ark/products/212633/intel-xeon-gold-6338n-processor-48m-cache-2-20-ghz.html 

[ct73]

Hi,

Thanks for the reply. What I am trying to do is port the Wind River Helix hypervisor to a server running a Xeon 6338N CPU. In Helix there is a BSP function that builds an internal data structure that includes the CPU clock and the bus clock. It reads CPU ID register 0x15 and calculates the frequencies as:

CPU clock = (Ecx * Ebx) / Eax

Bus clock = Ecx/1000

But, it will abort (and reset the system) if any of those register values are zero. For this processor the Ecx value always comes back zero.

Section 29.7.3 of the Intel software developers manual says:

For Intel processors in which CPUID.15H.EBX[31:0] ÷ CPUID.0x15.EAX[31:0] is enumerated but CPUID.15H.ECX
is not enumerated, Table 20-91 can be used to look up the nominal core crystal clock frequency.

But the table only has three entries. The table doesn't copy well unfortunately but the entries are:

Intel® Xeon® Scalable Processor Family with CPUID signature 06_55H.  25 MHz

6th and 7th generation Intel® Core™ processors and Intel® Xeon® W Processor Family. 24 MHz

Next Generation Intel Atom® processors based on Goldmont Microarchitecture with
CPUID signature 06_5CH (does not include Intel Xeon processors). 19.2 MHz

The 6338N is an Intel Xeon Scalable Processor but the CPUID signature is 06_6A so it doesn't fit any of those descriptions. Do you know how I can get the CPU and bus clock frequencies?