Re: G4 (7447A) CPU and dynamic frequency scaling

[Radek Kujawa <radoslaw.kujawa%c0ff33.net@localhost>]

Hi

On Jan 6, 2009, at 5:17 PM, Joel Carnat wrote:

> - do the 7447A really support CPU frequency scaling (at software  
> level) ?
As far as I understand MPC7450 Reference Manual (which covers also  
7447A), it is possible to control frequency by writing appropriate  
values to HID register.

> - do NetBSD support this ?
I don't think so.

> - what does "powersave: 1" mean ?
This is CPU-dependent. In 7447A case it means "Nap mode and Dynamic  
Power Management is enabled".

Quotes from MPC7450UM:

"Nap mode disables clocking in the MPC7450 core but maintains the lock  
on the PLL. (...)
Nap mode reduces power consumption by halting instruction fetch and  
dispatch, disabling bus snooping. Only the decrementer/time base  
registers, the PLL, and JTAG logic remain in a powered state."

"Dynamic Power Management - If an MPC7450 functional unit is idle, it  
automatically goes into a low-power mode. This mode does not affect  
operational performance. Dynamic power management automatically  
supplies or withholds power to execution units individually, based  
upon the contents of the instruction stream. "

Source of interest is sys/arch/powerpc/oea/cpu_subr.c and sys/arch/ 
powerpc/powerpc/powerpc_machdep.c

Regards
Radek