Back in April we reported on the successful launch of the SpaceX Falcon 9 rocket to the International Space Station which carried, along with supplies and experiments for the orbiting outpost, the RemoveDEBRIS spacecraft. Developed by the University of Surrey, RemoveDEBRIS was designed as the world’s first practical demonstration of what’s known as Active Debris Removal (ADR) technology. It included not only a number of different technologies for ensnaring nearby objects, it even brought along deployable targets to use them on.
Orbital debris (often referred to simply as “space junk”) is a serious threat to all space-faring nations, and has become even more pressing of a concern as the cost of orbital launches have dropped precipitously over the last few years, accelerating number and frequency of new objects entering orbit. The results of these first of their kind tests have therefore been hotly anticipated, as the technology to actively remove debris from Low Earth orbit (LEO) is seen by many in the industry to be a key element of expanding access to space for commercial purposes.
Breaking out the Sega Saturn out of the closet for a hit of 90’s nostalgia comes with its own set of compromises: the wired controllers, the composite video, and worst of all that dead CR2032 battery behind the backdoor. Along with the death of that battery went your clock and all those precious hours put into your game save files. While the bulk of us kept feeding the insatiable SRAM, a friendly Canadian engineer named [René] decided to fix the problem for good with FRAM.
The issue with the battery-backed memory in the Saturn stems from the particularly power-hungry factory installed SRAM chip. Normally when the console is plugged-in to a main power source the CR2032 battery is not in use, though after several weeks in storage the battery slowly discharges. [René’s] proposed solution was to use a non-volatile form of RAM chip that would match the pinout of the factory SRAM as close as possible. This would allow for easier install with the minimum number of jumper wires.
Enter the FM1808 FRAM chip complete with a whopping 256 kb of addressable memory. The ferroelectric chip operates at the same voltage as the Saturn’s factory SRAM, and has the added benefit of being able to use a read/write mode similar to that of the Saturn’s original memory chip. Both chips conform to a DIP-28 footprint, and only a single jumper wire on pin 22 was required to hold the FM1808 chip’s output-enable signal active-low as opposed to the active-high enable signal on the Saturn’s factory memory chip. The before and after motherboard photos are below:
After a quick test run of multiple successful read and writes to memory, [René] unplugged his Saturn for a couple days and found that his save files had been maintained. According to the FM1808 datasheet, they should be there for the next 45 years or so. The only downside to the upgrade is that the clock & calendar settings were not maintained upon boot-up and reset to the year 1996. But that’s nothing a bit of button-mashing through couldn’t solve, because after all wasn’t the point of all this to relive a piece of the 90s?
We live in a time when you don’t have to know assembly language to successfully work with embedded computers. The typical processor these days has resources that would shame early PCs and some of the larger ones are getting close to what was a powerful desktop machine only a few years ago. Even so, there are some cases where you really want to use assembly language. Maybe you need more speed. Or maybe you need very precise control over timing. Maybe you just like the challenge. [Robert G. Plantz] from Sonoma State University has an excellent book online titled “Introduction to Computer Organization: ARM Assembly Langauge Using the Raspberry Pi.” If you are interested in serious ARM assembly language, you really need to check out this book.
If you are more interested in x86-64 assembly and Linux [Plantz] has you covered there, too. Both books are free to read on the Internet, and you can pick up a printed version of the Linux book for a small payment if you want.