Date: Thu, 23 Oct 2003 02:23:37 -0400 From: Fluxstringer <[EMAIL PROTECTED]> Subject: Re: Cuda button: what it is/does
If removing the battery dumps the PRAM info and the Cuda chip controls hardware management info stored in PRAM (?) how does the result differ ? Even if this info is stored somewhere else it takes current to keep it stored . With the AC disconnected pulling the battery will eliminate any info not stored on a PROM or EPROM neither which am I aware of on a Mac motherboard.
The item which no-one has mentioned is the NVRAM (non-volatile RAM) chip. This is an 8KB chip of static RAM (very low power) which is powered by the battery when the machine is off. Many Open Firmware settings including the NVRAMcr are stored in the NVRAM. Open Firmware is the OS which the Mac runs before it loads the Mac OS and it touches on all the low level hardware stuff that can screw up your machine. Having corrupted NVRAM contents can remove all life signs from a machine as several people learned in the early days of OSX installation on our unsupported machines.
The NVRAMrc is an area in NVRAM where OF scripts are stored. These are the little things that modify the early behaviour of the machine, such as XLR8's (or was it PowerLogix's?) "virtual firmware" concept. The scripts in the NVRAMrc can have very powerful effects at the hardware level. One limit on our machines is that there are so many scripts fixing old problems, that all the NVRAMrc space is often used and there's no room for more NVRAMrc for new PCI cards or such.
Unplugging the machine and removing the battery will reset the NVRAM. However, the SRAM chip uses so little power that it is possible it may retain its contents for a significant amount of time just drinking the charge in the capacitors on the motherboard. Hence, it is recommended that one unplug the machine, remove the battery and hold down the CUDA switch for a time (30 seconds or so) to drain all the residual charge in the machine.
I'm not sure whether zapping PRAM or pressing the CUDA switch also resets the NVRAM chip. Apple is aggravatingly inprecise about the exact function of each of these procedures.
Jeff Walther
Thanks Jeff that explains a lot. But I wonder. Does the machine have to be plugged in or at least have a battery installed in order for a Cuda reset to be effective ? What I mean is, I assume current must be present in order for the machine to recognize the new hardware configuration.
Adrian
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