Q: I'm having problems with our caching drivers on the PowerMac 9500. Our drivers allocate a large (up to 4 MB) amount of RAM early in the boot process. If I set the driver's cache size to 4 MB, the computer locks up as soon as the driver is executed. If I set the cache size to 2 MB, the driver loads, and executes properly, but the computer gets a bus error much later in the boot process (after MacsBug loads, and after the MacOS screen is displayed, but before Finder executes). If I set the cache size to 1 MB, everything runs properly. What's going on here?

A: Because of OpenFirmware requirements, the boot stack on the new PowerMac 9500 CPUs was moved to 4MB. As a result, you can't grow the system heap past 4 MB or a system crash will occur.

If possible, try to defer allocating memory until INIT time. The 'sysz' mechanism is supported by the enabler ('boot' 3) when loading INITs.

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