It seems strange that RAM is being added to a computer so late in the build, but [Quinn Dunki] must have had it in the back of her mind the whole time because it turns out to be a rather painless experience. For those of you keeping score, this makes her Veronica project Turing complete.
The brightly colored rats nest pictured above connects the new components to the 6502 computer backplane seen in the upper left. [Quinn] decided to go with two 32K SRAM modules which need very little in the way of drive hardware (it’s hanging out on the breadboard to the left). The RAM module will simply listen for its address and react accordingly. There is one hitch regarding a two-phase clock and the need to protect the RAM from erroneous data during the first of those phases.
Getting this all to work actually pointed out a bug in the ROM module she had long ago completed. After picking up on the problem she was able to correct it simply by cutting traces and soldering in jumper wires.
For last year’s Toorcamp, the folks over at DorkbotPDX helped out with the Church of Robotron installation. A religion founded on the prophesy of a cybernetic uprising in the year 2084 is a little esoteric even for us, so the Dorkbot crew wanted a way to make playing Robotron: 2084 a little more visceral. Using MAME and a few debugging tools, they were able to read the memory of a machine playing Robotron to extend the game into the physical world. When the player dies, lights go off, alarms sound, and the prophet of the Church of Robotron is pleased.
The setup at the Church of Robotron included a machine running MAME with a Robotron ROM. When events happened in the game, such as lasers firing or a player death, physical events would be triggered. To do this, the Dorkbot team read the memory locations of a game of Robotron at different times and found memory locations tied to in-game events. On their blog they go over using the MAME debug tool to detect a player’s death which can then be translated into physical apparitions for the Church of Robotron.
It’s a very cool hack, and one we wish we had a video of. Having a plastic ghost hit a player while playing Pac-Man seems like an awesome idea, and with the Dorkbot tutorial, it looks fairly easy.
There is buzz all over the reddits and Element 14 discussion boards about an updated version of the Raspberry Pi that bumps the amount of RAM from 256 MB to 512 MB.
This new update comes after the announcement of an upgraded version of the yet-to-be-released Raspi Model A (from 128 MB of RAM to 256 MB), and a few slight modifications to the Model B that include fixing a few hardware bugs (nothing serious) and adding mounting holes.
After perusing the Element 14 and Raspberry Pi discussion boards, a few things become apparent. Firstly, it appears this new upgrade to double the amount of RAM was initiated by manufacturers. It seems 512 MB RAM chips are cheap enough now to include in the Raspi without impacting the cost of components. Secondly, 512 MB seems to be the upper limit for the Raspberry Pi, at least for this iteration of hardware. Not enough address lines, they say, but you’re welcome to try and hack your own RAM to a Raspi CPU.
So far, attentive Raspi enthusiasts have found Raspberry Pis with double the amount of RAM on the UK Farnell site and the Australian Element 14 site. Nothing so far on the US Element 14 site, although we’ll gladly update this post when a Hackaday reader finds the relevant link.
EDIT: Here’s the link for the US version of Newark. No, there aren’t any in stock. Also, Hackaday beat the official Farnell/Element 14/Newark press release and the Raspberry Pi blog to the punch. Woo, go us.
For the longest time, hardware tinkerers have only been able to play around with two types of memory. RAM, including Static RAM and Dynamic RAM, can be exceedingly fast but is volatile and loses its data when power is removed. Non-volatile memory such as EPROMS, EEPROMS, and Flash memory retains its state after power is removed, but these formats are somewhat slower.
There have always been competing technologies that sought to combine the best traits of these types of memory, but not often have they been available to hobbyists. [Majenko] got his hands on a few MRAM chips – Magneto-Resistive RAM – and decided to see what they could do.
Magneto-Resistive RAM uses tiny pairs of magnetic plates to read and write 1s and 0s. [Majenko] received a sample of four MRAM chips with an SPI bus (it might be this chip, 4 Megabits for $20, although smaller capacity chips are available for about $6). After wiring these chips up on a home-made breakout board, [Majenko] had 16 Megabits of non-volatile memory that was able to run at 40 MHz.
The result was exactly what the datasheet said: very fast write and read times, with the ability to remove power. Unlike EEPROMS that can be destroyed by repeated reading and writing, MRAM has an unlimited number of write cycles.
While MRAM may be a very young technology right now, it’s a wonderful portent of things to come. In 20 (or 30, or 40) years, it’s doubtful any computer from the largest server to the smallest microcontroller will have the artificial separation between disk space and memory. The fact that any hardware hacker is able to play around with this technology today is somewhat amazing, and we look forward to more builds using MRAM in the future.
[Quinn Dunki] keeps rolling with her 6502 based computer build. This time around she’s added some memory to store the programs, but needed a way to get that code into the device. Above is her solution, a bank of hex switches used to program the 8-bit command and 16-bit address for each line of machine code.
This is a continuation of her Veronica project. The last time we saw it she had hardwired the logic levels for the data bus, but that’s no fun since nothing can actually be computed. [Quinn] picked up an SRAM chip which will store the program. It’s compatible with the 6502’s memory bus, but needs a bit of extra circuitry for her to be able to hand program it with this switch bank. She used some tri-state buffers to switch between connections to the processor, and to the hex switches. This way, she disconnects the RAM from the processor using the buffers, uses the switches and push button to clock in the program, then patches the RAM back into the computer.
Seeing this process in the video after the break certainly gives you an appreciation for what an improvement the punch-card system was over this technique. Still, seeing this is a delight that we’d like to try! Continue reading “Programming the 6502 one nibble at a time”
[Heli] had a WRT300N wireless router sitting around collecting dust. He decided to squeeze at bit more entertainment value out of it by seeing if he could pull off a RAM upgrade. He managed to double the router’s RAM and posted a walk through (translated) to help you do the same.
Swapping out surface mount RAM chips isn’t the easiest thing in the world and you must wondering what prompted this. It seems he wanted to run the LuCI package on the router but it was slow (or even incapable) of booting with the stock hardware’s 16 Mb. He first sourced some pin-compatible replacement chips from an old Pentium III computer. While his soldering iron was hot, he also wired up a JTAG header, which connects via the red wires just visible to the left. When he first fired up the unit he was happy that it was able to boot, but it still only detected 16 Mb.
It turns out you’re going to need to roll your own kernel to get it to take advantage of the upgrade. Source code for OpenWRT is easy to find and there’s plenty of guides for compiling it. If you try this, make sure to read [Heli’s] post carefully as he’s got some important configuration information that will help you to avoid bricking your router.
[Andy] stuffed some more RAM onto an Arduino Mega and his three-part walk through on the design, construction, and software is a great read and one of the more ‘hard core’ Arduino builds we’ve seen.
The build is centered around a 512K × 8 SRAM module [PDF warning]. Because the RAM is divided up into about 512,000 chunks of 8 bits, the Arduino has to access the RAM through 16 ‘address lines’, then send the data through 8 ‘data lines’. [Andy] didn’t want to use up 24 pins on his Arduino, so he used a latch to multiplex the lowest 8 address lines and the data lines together. With the 512KB RAM expansion installed, the Mega is able to address a whopping 520 Kilobytes.
We’ve seen a few builds that have been limited by the amount of RAM available in the Arduino, like capturing video and some robot hacks, and adding some more RAM to those builds would be great. Multiplexing data and address lines using a latch can be expanded even further, but 520KB ought to be enough for anybody.