V2.5 BOOSTER CURRENT PROTOTYPE STATUS (SEC BOOSTER)
Posted: Mon Aug 21, 2017 1:16 pm
I actually wasn't planning to produce the V2 booster again. Though a chap said he is interested in them to mod machines with. Though as they are "out of stock" now it caused a bit of a problem. Firstly, a batch of 25-50 PCBs of 6 layers isn't cheap. The production run would be well over £1,000. So it just wasn't viable to produce them considering sales are generally slow with boosters.
I had already spent some time tweaking the V2 design to use just 2 GALs instead of 1. Though in the end, I found it just couldn't be done. Just not enough IO pins
All 3 GAL's are basically chained in series for the logic operations, which doesn't help with trying to push into 32MHz speeds. In theory, it should run at 32mhz, but even the 32MHz drive on the STFM is so bad, it can only just drive the shifter, nevermind a extra gate in a PLD.
The STE had a buffer to do that job. So I made 2 previsions with this design. Buffering the 32MHz clock by the shifter, or just using a 32MHz oscilator. The fallback is just using 16MHz.
Now while the STE booster works at 32MHz, the STFM has more screwy timings to contend with. This makes 32MHz more of a problem. I stopped work on this project for a long time as I just didn't have time (or really any interest at the moment) to finish the beta board off. Though now it has just gone off to fab.
This new board uses a large Atmel PLD. I have used it before on my dev-system board. Though even that I have not been able to run 32MHz. Though I made some more previsions with this new V2 design (dubbed V2.5) to run /DTACK via the PLD so I can stall the CPU a little and hopefully this will get 32MHz working. Though as time is a factor. I don't know when I will get time to write the new code or try it out. Though in theory, getting it running as 16MHz shouldn't take to long. Assuming I've not screwed up anything in the mad rush to complete the design.
The boards can be made in batches of 3 now. So while I don't have to spend £1,000+ on a new batch, the price per PCB is a lot higher. This means the booster end price will be a fair bit higher. Though I am not even sure if I will sell these myself for my store or not yet.
There was some previsions also to adapt the booster logic for software switching. I did some draft designs several months ago and started to route the PLD logic. Though that is as far as it got. I can't even remember how I was planning to go about it now. But its possible firmware updates for the V2.5 could be done to add features or "fixes" for 32MHz speeds in the future (if solvable).
As for the software switching. I think there was plans to have my own "exxos register" somewhere to allow the booster to be turned on or off. Really this is just a bypass for the toggle switch, where that bit is mapped to a register in the memory map somewhere. A latch in the PLD and some logic to route to the switching code shouldn't really be a problem. I actually routed 8 data bits to the PLD for maybe other use such as ROM switching.
One thing to bare in mind, is settings are not stored anywhere. So once the machine is powered down, the defaults would be selected again. Though I do not have any plans to do another V2 design, as the STE booster should have similar logic and the settings will be stored in the RTC NVRAM. Though it is likely a long way off before that project is completed.
Overall, this V2.5 booster is a clone of the V2.2 booster, only using a more advanced PLD with a lot more IO power for various "possible" features at a later date.