• Latest prototype boards are in!

    Ross Bamford02/15/2022 at 21:10 0 comments

    It's been pretty quiet around here lately, as I've been kind of focused on the Classic Version 2 of the original rosco_m68k , and have also been super busy with my new day job, but things have continued quietly progressing behind the scenes. 

    The Pro has been through a couple of revisions now. The free-running board I posted about in the last log had some pretty silly mistakes so needed a respin pretty much right away. However, with those fixed the board finally ran some code, and I made a start on the pro-specific firmware, including spinning up the onboard SD card and other things (all made much easier by the fact that a lot of the code can be reused from the Classic).

    It's worth noting that it's actually running at 20MHz here, and not 0.0MHz - the speed calculation code wasn't ported to 68030 at this point! Once that was done, we got some sensible speed readouts, and I did a quick Dhrystone run,  just to get a feel of it:

    Once code was running, I turned my attention to getting the onboard peripherals working, starting with the awesome Xosera video adapter. That led me to discover a few more errors (some silly, some slightly less-so) in the design, which meant some bodge wires and a whole bodge PCB to turn one logic chip into two were needed:

    (Notice the bodge PCB daughterboard in the lower left. Also, it's not super-visible in this picture, but the 74245 I'm using for Xosera level shifting in the upper right - the one with the wires - is actually stacked on three sockets to rewire the pins with those bodges).

    Closer view of the "bodge daughterboard":

    With those hacks in place, we had VGA output!

    There's still some issues to work out, notably a (suspected) bus timing issue with the Xosera accesses that's causing some interesting issues when writing to the video RAM quickly (like, when software-scrolling a text screen):

    But all-in-all, I'm very happy with the progress. The bodges and hacks shown on the r3 prototype above are all now worked into a new r4 prototype, which arrived back from the fab this week. It's now at a point where it's "good enough" that it's worth others populating a board, so I'm sending a few out this week (including one to Xark, who's kindly agreed to help me track down the Xosera scroll / fast write issue). 

    The latest board looks like this:

    As always, everything is available on Github, and you can find more about Xark's Xosera retro video adapter both here on Hackaday and over on his Github.

    That's all for now, I'll update again when I have one of these new board populated! 

    Oh, and if updates here aren't coming frequently enough (and for that I apologise) you can always join us on Discord :) 

  • Free-running prototype and first steps to code

    Ross Bamford11/08/2021 at 22:28 0 comments

    The prototype board I logged about recently came back from the fab, and as a first test (just to sanity check the components really) I got it free-running. Happy to say the CPU and reset / power circuitry seem to be just fine :) 

    I'm now working on getting it running some actual code. So far I've identified a few issues in the GALs (which I coded blind) and some bodge wires needed on the board, but that's what a prototype is for, after all :D 

    As soon as I've something to show, I'll update here!

  • First prototype out for production!

    Ross Bamford10/11/2021 at 19:52 2 comments

    Things are moving pretty fast here, and I recently sent the first prototype rosco_m68k_pro board out for production!

    The aim with this is only really to prove out some of the basics of the architecture, and it's missing a lot of stuff that will go on the final boards (such as interchangeable CPU/FPU modules, expansion slots, IDE and lots more), but it will at least prove that the basic 68030 bus architecture works with the programmable logic and that the fundamental design is sound. It'll also prove out the on-board Xosera video adapter (for now on an UPduino, in future boards the FPGA will be on-board too).

    That's all for now, I'll update further when I have them back from the fab!