V2.5 BOOSTER CURRENT PROTOTYPE STATUS

Help & information about the V2.5 booster.
Petari
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Re: V2.5 BOOSTER CURRENT PROTOTYPE STATUS

Post by Petari » Sat Jan 06, 2018 8:55 am

Something is not clear for me here. 68HC000 CPU is stated as cycle identical with 68000. How then it can do VDI operations with more than 400% speed ? (at 32 MHz CPU clock) . Especially considering that RAM access is still 100% speed. Is it because blitter is enabled ? Maybe to compare with blitter on reference ?

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Re: V2.5 BOOSTER CURRENT PROTOTYPE STATUS

Post by exxos » Sat Jan 06, 2018 9:43 am

Petari wrote:
Sat Jan 06, 2018 8:55 am
Is it because blitter is enabled ?
Yes.
Petari wrote:
Sat Jan 06, 2018 8:55 am
Maybe to compare with blitter on reference ?
This uses 32Mhz as reference machine, and then 38Mhz system.


Image

Tests were faster once 40Mhz was reached, but was to unstable to run proper tests.
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Re: V2.5 BOOSTER CURRENT PROTOTYPE STATUS

Post by exxos » Mon Jan 08, 2018 10:24 am

I did some testings with adding /DTACK into the switching code (was actually on the STE but relevant here). The problem is with DTACK, is that for ROM access for example, the GLUE doesn't release DTACK until a few nanoseconds before address strobe goes low again on the next cycle, basically around S2. The problem here is, the CPU is running at high speeds, it can reread DTACK from the previous cycle and obviously cause a crash.

So I did a quick test and added DTACK into my speed switching code to see exactly what happens in waiting for DTACK to go high before allowing 32 MHz speeds..

I got 266% on ROM speed (should be 309%)

I added 1K pull up on DTACK, then got around 295% (give or take 5%) .. Still a fraction slow.. but only a few %...

So GLUE is what has DTACK almost low all the time... and main cause of crappy DTACK generation.

There could be something else with slow DTACK release which could account for a few % drop in speed somewhere.. but no idea what. It does seem a little odd that speed seems to vary now, it is like DTACK is not arriving at a constant speed causing around 5-10% variation in ROM access.. So this would be difficult to determine.

But really, in the case of the STFM, ROM decoding is done on the booster board anyway. So this rules out likely issues with DTACK. On the STE however, I use the GLUE logic for the decoding as it is fast enough for 32 MHz. Though it is likely this logic will have to be bypassed in order to create a proper DTACK signal.

But in any case, when thinking towards the 64 MHz, the DTACK issue could be a problem, but the least I have a easy solution for this and it is fixable at least :) it is possible slowdown with this new code, could be compensated by the faster CPU anyway.. In that the CPU will start cycles twice as fast, and compensate the slowdown with using DTACK which delays a clock cycle.

Worst case currently is that a few percent is lost, but overall again should be higher with 64Mhz anyway, so it does not really matter much.
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Re: V2.5 BOOSTER CURRENT PROTOTYPE STATUS

Post by exxos » Mon Jan 08, 2018 11:30 am

As a update, I did a whole bunch of tests.. Long story short, changing to 500R resistor on DTACK made a whole world of difference..

dt11.png
dt11.png (6.61 KiB) Viewed 130 times
On the left, is 1K resistor... On the right is 500R resistor.. Not a great deal between the two, but makes a dramatic difference in results..

Basically now, worst case looks like about 1% variation in results. But this is about as good as things get anyway.

I really don't know why DTACK is such a "heavy" signal to pull-up :roll: I did a quick measurement of capacitance and read 250pF.. They may not be accurate due to the pull-up resistance being in the mix also.. But with a lot of gates to pull-up on chips, it probably isn't far off...

I did a close-up also..
dtz.png
dtz.png (79.54 KiB) Viewed 129 times

I also did a quick simulation..
sct.JPG
sct.JPG (18.61 KiB) Viewed 127 times
res1.JPG
res1.JPG (40.46 KiB) Viewed 127 times
So on my actual scope results I see that around 50% through the cycle (about 150ns) in must reach about 4 V.

On my simulation circuit, I see 4V around 200ns.

Of course there will be a lot of factors and this was only quick test, but it seems that the capacitance is indeed around 250pF. Which does not seem much, but it is clear you can take 200ns to get to 4volts. If we assume 2 volts as a logic one, then the time will be closer to 100ns.

500R on 5V is 5V / 500 = 0.010Amps (10mA) which is a lot really, I quickly checked the MFP datasheet and it quotes 5.3mA.. So likely in reality a 1K resistor should be the lowest value used about starting to strain the DTACK drive transistors.

A possible workaround could be control the 500R resistor by the PLD. In that when address strobe goes high, it connects the 500R resistor to DTACK and allows resistance to be pulled up faster. Then when address strobe goes low, the resistor is isolated so the actual DTACK resistance would be normal like 2.2K. This way DTACK switches to 0V with 2.2K as normal, and is pulled up high with 500R...
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Re: V2.5 BOOSTER CURRENT PROTOTYPE STATUS

Post by exxos » Thu Jan 11, 2018 7:01 pm

Tried the PLL finally.. Wired it for x2, so 8MHz input, 16 MHz output...

Just seem to get varying speed for some reason :roll:

pllmess.png
pllmess.png (4.12 KiB) Viewed 105 times
pll2.png
pll2.png (5.28 KiB) Viewed 105 times
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

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Re: V2.5 BOOSTER CURRENT PROTOTYPE STATUS

Post by exxos » Thu Jan 11, 2018 10:20 pm

OK, so small update.. I switched to x10 on my scope probes and it is now stable at 16mhz.. BUT..

What I did not realise before, is on the STE...The 32mhz goes to 16mhz and is in sync perfectly.. but whatever is clocking down the 16mhz to 8mhz has a 16ns delay.. so its not in sync..So the PLL starts out 16ns out of sync... So the PLL 16mhz and ST 16mhz are also 16ns out of sync.

This means the STE screws up on floppy access, which it doesn't do when using the 16mhz ST clock.. but the PLL clock is 32ns "behind" the 8mhz and its to much and it screws up.

I could probably do some work arounds on the on a larger PLD based design, but not on the simple STE booster..But, this shouldn't be a problem on the STFM as the clocks are all perfectly in sync..

So I will try and find some time tomorrow to try the PLL on a STFM booster. The STFM is the one which a problematic 32mhz circuit.. so I am not to bothered about the STE issues with it.
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Re: V2.5 BOOSTER CURRENT PROTOTYPE STATUS

Post by exxos » Fri Jan 12, 2018 11:56 am

Right, working now :) I used the 16mhz input and x2 PLL for 32mhz output (to "bypass" the 16ns 8mhz skew issue)

Turns out the ST clocks are in sync on the falling edges of the clocks, and the PLL is syncing on the rising edges...


ST CLOCK 16 & 32
1632st.png
1632st.png (4.95 KiB) Viewed 71 times

PLL 32 & ST 16
1632.png
1632.png (4.96 KiB) Viewed 71 times
So I fiddled with the GAL code to invert the 32mhz input and now everything is happy again :)

Oddly I have some "bug" now which has resulted in a few % extra in speed :lol:
bug.jpg
bug.jpg (109.42 KiB) Viewed 71 times

EDIT:

Oddly now and then it crashed, so I took the scope probes off the ST 16MHz line and all was fine, but the speed went back to normal again.. put the scope probe back and higher speeds again.. odd..

EDIT2:
OK, seems the PLL latches onto 32.89mhz sometimes, other times 32.25mhz... now I want to try x3 on the PLL but not going to be easy to re-wire it as I intended to basse on 8mhz not 32mhz :roll:
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Re: V2.5 BOOSTER CURRENT PROTOTYPE STATUS

Post by exxos » Mon Jan 15, 2018 7:35 pm

1.jpg
1.jpg (118.79 KiB) Viewed 21 times

Add a little fun earlier.. I took my RSO which I design for the CT60 while ago.. The clock multiplier is way too high for this test, so just a matter of lifting up a pin on the chip to half the output frequency from 100mhz to 50mhz kinda thing. Pin was tiny and ended up snapping off, but thankfully this pin needed to be floating anyway so it didn't matter :lol:

I tried various methods of getting more speed, but I did not break the speed barrier of what I got before of around 38Mhz. I really did not expect it to go any faster. I was just doublechecking that the CPU was maxing out at this frequency.

I still need to finish off the SEC PCB design yet :( but I got a little sidetracked in testing the PLL out before I added it to the PCB layout.. Hopefully I can find time tomorrow to try out the PLL on the STFM make sure I am happy with it before continuing with the SEC design..
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

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