ADC Home > Reference Library > Technical Q&As > Legacy Documents > Hardware & Drivers >

Legacy Documentclose button

Important: This document is part of the Legacy section of the ADC Reference Library. This information should not be used for new development.

Current information on this Reference Library topic can be found here:

Problems with Caching Drivers on PowerMac 9500

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.

[Sep 15 1995]

Did this document help you?
Yes: Tell us what works for you.
It’s good, but: Report typos, inaccuracies, and so forth.
It wasn’t helpful: Tell us what would have helped.