Project Introduction: Trollbook, a Homebrew 68040 Computer
For a while now, I have worked with h4xxel to build a palmtop computer based on a 68040 processor. I couldn't find many references to homebrew 68040 computers on the internet, so I figured I should write some about it.
1 Overview
The project is about building a homebrew palmtop-ish sized laptop with a 7" screen driven at 256 colors from a 16-bit palette. We first started on a 68030 based design and a Xilinx CPLD for glue logic. This was a mixed voltage system on a two layer board. It was messy, needed a re-design and work halted.
Maybe a year later we found a 68040FE33V on ebay and decided to buy it for the design instead. The board was redesigned to be a 4-layer board and the CPLD was replaced with an FPGA we got from a surplus electronics store.
The intention is to make a separate board with a keyboard, power supply, SD card holder, expansion slot and some other miscellanieous parts. The current plan is to use two 2000 mAh LiPo cells in series for battery power, which should give a bit over two hours of runtime.
2 Current Status
Figure 1 - The current development setup for the hardware
Currently, our main board has everything populated that will be on the mainboard. This includes the CPU and FPGA, 8-bit stereo audio DAC, 512 kB of SRAM (for framebuffer and second stage BIOS code), 64 MB of SDRAM (exclusively for the CPU), 512 kB of SPI flash, VGA DAC, and oscillators.
With this setup, combined with a 7" 800 by 480 resolution screen, the system can boot either by loading an iHEX over UART, or from the on-board SPI ROM. The initial (stage 1) bootloader is located in a small (512 byte) ROM inside the FPGA. The second stage BIOS/bootloader can do a few different things like browse the SD card, write a file to framebuffer from the SD card and launching an ELF binary from SD-card, setting up and enabling the MMU in the process.
A few temporary boards have been constructed with power supply (+3v3, +24v), SD card holder and keypad. Next stage is implementing HDL for audio, interrupts and a timer. To go with the computer, we have hacked together a system emulator for testing code on without access to the actual hardware.
We have also started writing TrollOS, a Unix-like operating system for Trollbook, although we may port Linux or some BSD to it at some point.
A video showing the current status of the project can be found on youtube: Trollbook: First demo
There has been a lot of struggles to get this far, but that's for another blog post. More to follow...
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