>Ok, you have to think this out a bit more. Do you remember 286's? I do, I >have one. It is 3 times the speed of a gameboy, yet I still feel like >popping the thing open and pushing the data (whenever I'm forced into using >it). But this is only due to inefficiencies in the operating system, and the slow secondary memory. Running a 286 or even an 8088 computer completely from ROM or RAM is very fast. My Zenity Minisport 8088 laptop (8 MHz) has DOS 3.1 in ROM and a 2 meg ram disk, everything runs *very* quickly. No latencies. >Keep in mind as well that the 4mhz is the max speed of the processor, >that does not mean its ever going to get to 4mhz while doing some >processing (in fact, it probably won't). A 6mhz z80 in a calculator (The >TI-8x series) can be clocked at 2mhz. Say you can reach 2mhz with the z80 >in the gameboy. Don't forget now that you'll want some I/O there, because >of the need of a hard drive and other such devices. After this, what speed >do you think you'll reach? Ummm :) No processor switches clock rates during operation (well actually some do, but generally small embedded processors don't). The TI-8x processor always runs at about 6 MHz. It only slows down in the TI-8x because the clock is not crystal controlled, and battery life can affect the clock rate because the clock is a cheap RC pair. But in most other devices, gameboy included, they are clocked with a crystal and the clock rate will never vary more than 0.1%. As has been previously stated in this list, an 8 bit processor is *plenty* fast enough to do 90% of the tasks a PDA or simple wearable would need. And depending on the type of 8 bit processor you choose, they can have all the I/O, serial ports, timers, interrupts, etc. that even their 16 and 32 bit cousins can have. NEC even makes *4 bit* processors which have hundreds of pins, built-in LCD and memory controllers, and tons of I/O!!! So as you can see, 8 bit won't go away any time soon. They just do things slower. >As far as 25 hours of life, don't expect half that. You're going to need >power for the hard drive (which is basically an improbable addon), Yep, don't even bother with attempting to add a hard drive to the game boy. It's far more work than it's worth. >the HMD >(even if you use the screen as I suggested, you may need to make some >modifications), and any other device you have hooked up to it (which will >probably entail an I/O card so you can add things on later). True, a hard disk alone will kill the battery life of most any system. The typical laptop hard drive can draw as much as 0.5 amps, and this will eat through 4 AA's in 15 minutes. Add some sort of backlit or color HMD and the batteries required alone will cost as much as your entire wearable. >While it would be nice, it may be more... effective... to think about some >other chip, such as those used in PDA's (Such as the NEC VR series, my >choice). Problem though is that the complexity of these systems rises exponentially with processor power. You have to guage what you want with how much time you're willing to spend developing. While the NEC VR chips are cheap, super high performance, and use very little power, the simplest VR chip is a 120 pin quad flat package! Most of the VR's suitible for wearables (the VR41xx series) are 180 or more pins. There's *no way* you can homebuild a circuit board in which this chip can be mounted. You must resort to expensive board fabrication houses, and expect to pay $200+ just for a few prototype boards. Couple this with the fact that most of these 32 bit chips require 16 or even 32 bit wide memory datapaths, which makes your board complexity go through the roof, unless you can find chips with large on-chip memories. But even still you'll have to add RAM which rarely ever comes on-chip. The PDA manufacturers can get away with using these big complicated chips because they included huge and expensive FPGA chipsets along with 4 or even 8 layer printed circuit boards, which allows their entire system to fit in small spaces. Few people can afford these luxuries when their goal is a low cost wearable. So people, unless you're an experienced embedded system designer, don't discount 8 bit systems, otherwise you'll be spending 6 months just for design R&D :). -Mel ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -http://www.egr.msu.edu/~tsaimelv/expander.htm
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