stripes
Member
Registered: Sep 1999
Location: VA, USA
Posts: 27 |
The DragonBallEZ doesn't use another chip for memory I/O (or most other I/O either!). that's part of why it is popular for low cost and compact applications.
It does have a limited number of chipselect lines (which basically stear memory accesses to a device, like a ROM/FLASH or RAM, or the springboard). I think it has four, but I don't know for sure, would have to look at the databook to be sure (Mot's link is scrod, I can see the databook entries at http://www.mot.com/SPS/WIRELESS/doc...tion/index.html but I can't get to them).
The springboard gets two of them, I assume the RAM gets one, and the OS/app ROM gets the other.
Each can address 16M (24 address pins). So the CPU can see 32M on a springboard with ease. You could do more by say using one 16M space to select the other (bank switching, ask an Apple II programmer). It is unplesent for many tasks, but could be mostly transparent for others (like holing applications for the Launcher, or DB files the OS copies into "real RAM" when they are accessed by an application).
I think the real reason handspring used two chipselects for the springboard is so one can easally be used for the (FLASH?) ROM holding the application, and the other for talking to the hardware, avoiding the need to select on the address pins, making each springboard a tiny bit cheeper.
As for PalmOS itself it handles as many memory "slots" (or maybe they call it "cards") as you could ever possably stuff into a device (thousands). Each one can be independently inserted and removed (not that any PalmOS platform prior to the Visor actually did that!). Each is limited to 16M, but I don't think there is a deep meaning for that (i.e. they don't give you a 32bit "pointer" with 9 bits used for something else). Even if it could only support 16M per "card" any physical device could just appear as multiple cards to the software anyway.
There, that sure was long winded :-)
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