Franklinstein
Well-known member
For those familiar, the PowerBook 2400c's logic board has spots on the logic board for four VRAM modules, but only two are populated to provide the normal 1MB of VRAM in these. However, the Chips 65550 video controller here (and in the 3400) can support up to 2MB using four 256x16 EDO VRAM modules.
I tested expanding this on the hardware side and while it looks like the new modules are recognized (there were new video artifacts on screen due to a bad solder joint on one of the new chips, subsequently repaired), System software doesn't see it/cant't utilize anything beyond the 1MB it's expecting. This suggests that the 1MB is a fixed size somewhere either in ROM or wherever the video driver is present in the System Software on these.
According to the user guide for the 65550 on page 13-12, I have to somehow set part of register XR43 to 01 to reflect 2MB of memory. On a reset this value defaults to 00 for 1MB. I figure ResEdit can be utilized to change the configuration if I can find the resource in the OS but I'd probably be out of luck if it's in ROM; I'm nowhere near good enough in software to build a ROM patch.
Has anyone ever tried to hack the video system on a 2400 or 3400? Any suggestions where to look for the video driver? These don't seem to have a discrete Extension.
I tested expanding this on the hardware side and while it looks like the new modules are recognized (there were new video artifacts on screen due to a bad solder joint on one of the new chips, subsequently repaired), System software doesn't see it/cant't utilize anything beyond the 1MB it's expecting. This suggests that the 1MB is a fixed size somewhere either in ROM or wherever the video driver is present in the System Software on these.
According to the user guide for the 65550 on page 13-12, I have to somehow set part of register XR43 to 01 to reflect 2MB of memory. On a reset this value defaults to 00 for 1MB. I figure ResEdit can be utilized to change the configuration if I can find the resource in the OS but I'd probably be out of luck if it's in ROM; I'm nowhere near good enough in software to build a ROM patch.
Has anyone ever tried to hack the video system on a 2400 or 3400? Any suggestions where to look for the video driver? These don't seem to have a discrete Extension.