GekkoScience BM1384 Project Development Discussion

[sidehack]

So, I currently have three tested functional BM1384 breakout boards. I didn't get any further work done on the regulator for doing that and other things. But one of the breakouts is heatsinked and running on Eligius pointed at the burger address (http://eligius.st/~wizkid057/newstats/userstats.php/1BURGERAXHH6Yi6LRybRJK7ybEm5m5HwTr)

I think the regulator problems are temperature-related. I hope to have time to look at them tomorrow, but our wire cutter went down today and I have to weld/machine some parts back together to get it going so we can meet orders. Grumble grumble Chinese steel grumble grumble.

[gexain]

exellent project development

[sidehack]

So yesterday evening I finally got the wire cutter parts re-machined and reassembled, but today was a maintenance day for hosting and stuff around the shop. So very little progress. We've had the protoCompac mining on the 1Burger at Eligius at 125MHz (about 6.8GH) for the last 24 hours without any problems. I have noted the chip doesn't like to start below 0.65V, which might help explain what some people were seeing with S5 undervolt testing. That's about 10V across an S5 board. I'll probably change up the regulator voltage range to start about 625mV and run up to about 800mV.

I'm working on using the RF pin to trigger sent-share LED like on the U1/U2 but having no luck. The flag is pulsing with a short-enough duration that persistence of vision keeps me from seeing an LED change with the setup we have. I can make it work with a one-shot circuit but it'll take some extra dev time and a bit more board space. Hopefully I can keep things simple. Having a flashing sent-share LED is way better than not having a flashing sent-share LED.

I'll probably be on Compac all day tomorrow. Hopefully I can get enough ironed out that we'll be sending off for actual prototype PCBs early next week.

Also, tomorrow is Friday which means Cheeseburger Day. So I won't actually be working all day. Gotta make time for sammiches.

[MrTeal]

Also, tomorrow is Friday which means Cheeseburger Day. So I won't actually be working all day. Gotta make time for sammiches.

How many sammiches are involved in a typical Cheeseburger Day?

[sidehack]

I typically eat 3 cheeseburgers, 5 hashbrowns and between 6 and 8 glasses of tea.

[Unacceptable]

I typically eat 3 cheeseburgers, 5 hashbrowns and between 6 and 8 glasses of tea.

Sweet tea   & I'm not making a pass at you  

[sidehack]

Yes, sweet tea.

[daddyfatsax]

With ice. It is already getting warm down South.

[sidehack]

Got LED stuff figured out and the board design modified to reflect the changes in LED drive and regulator. Sent an updated heatsink spec to the heatsink people. I'll have to do some recalculating on the regulator to shift the adjustable range from 0.65 to 0.80, instead of 0.55 to 0.75 since it appears the chip won't work on most of that low range anyway. As this affects the feedback values, it also affects the frequency compensation values so will require some more testing.

By the way, the LED color scheme is pretty sexy.

I'm also going to rig up a USB extension, possibly externally powered, that'll allow me to directly measure input power so we can get some sample efficiency curves off the prototype boards. Since the various modules (right now two PCBs, one of Novak's Prisma adapters and some breadboarding) are basically identical to the Compac as it stands, the power requirements should be pretty close to accurate.

Also, we're currently at a board size of 1x2.16 inches which puts it at almost the same size as an Avalon Nano (slightly narrower, slightly longer). The heatsink we're looking at to be 25mm square and top-mounted, which means the fins are facing upward on basically all the PC USB ports I have looked at. The AntMiner U2 heatsink is 25x40mm. If we were doing rear-side heatsinking I could use a full 25x50mm heatsink but I'm not sure how much cooling comes from the bottom on this chip, given Bitmain has zero designs using bottom heatsinking. I don't know if that's because the chip is designed to top-cool, or because of potential ground plane issues with string designs, or both.
If people are concerned about requiring a larger heatsink, I can get a larger heatsink and not change the Compac PCB size, where the extra length of heatsink will be sticking out past the end of the board.

If we end up doing the Amita (the two-chip string) as well, the board will probably have to be wider to accomodate some extra buffer capacitors to help out with node-level core voltage stability. Since I'm planning on just using two Compac heatsinks on the Amita instead of spec'ing a second heatsink, any changes to the heatsink dimension will cause additional changes to the Amita dimension, as the board length will have to accomodate a full heatsink plus as much of a second as doesn't overhang the board.

The total thickness, given that the heatsink will be on the same side as the rest of the parts, should be no more than 14mm. This is PCB thickness plus ASIC thickness plus a small shim plus 10mm heatsink. I figure y'all guys with compact hubs should appreciate this dimension.

[TheRealSteve]

Also, we're currently at a board size of 1x2.16 inches which puts it at almost the same size as an Avalon Nano (slightly narrower, slightly longer).

Sounds like it'd be almost exactly the same size as the rectangular part of a hex•fury, which was a rather compact design for 6 chips

Sounds like it should fit quite nicely into the original BE cases and readily fit inside Antminer U1/U2 magnetic latch type cases.

Looks like the one under test (at the burger address) has been fairly stable as well - very nice!

[sidehack]

I'm not sure how much it's a problem of hot restarting or just that the prototype's pretty jankety right now with wires on headers flopping everywhere, but sometimes when it cuts out it decides not to come back online for a few minutes. I've noticed it's not as stable at 125MHz as it was at 100MHz, which could be heat-related or voltage-related. It'll take some more testing to be sure of which.
I pulled the test board this morning to play a bit with the LED drive, so that cost a few minutes of hashing, but it's been running alright basically continuously for the last two days and some. The regulator has no heatsinking, and the chip has about a 2cmx3cm thing taped onto it not very fancily.

I'm pretty sure we won't be selling these in cases. It adds to the cost and how many folks are going to just chuck 'em anyway?

[TheRealSteve]

I'm pretty sure we won't be selling these in cases. It adds to the cost and how many folks are going to just chuck 'em anyway?

Nah, but I might should I end up buying a bunch for reselling/gifting - wouldn't add that much cost on my end

[philipma1957]

Got LED stuff figured out and the board design modified to reflect the changes in LED drive and regulator. Sent an updated heatsink spec to the heatsink people. I'll have to do some recalculating on the regulator to shift the adjustable range from 0.65 to 0.80, instead of 0.55 to 0.75 since it appears the chip won't work on most of that low range anyway. As this affects the feedback values, it also affects the frequency compensation values so will require some more testing.

By the way, the LED color scheme is pretty sexy.

I'm also going to rig up a USB extension, possibly externally powered, that'll allow me to directly measure input power so we can get some sample efficiency curves off the prototype boards. Since the various modules (right now two PCBs, one of Novak's Prisma adapters and some breadboarding) are basically identical to the Compac as it stands, the power requirements should be pretty close to accurate.

Also, we're currently at a board size of 1x2.16 inches which puts it at almost the same size as an Avalon Nano (slightly narrower, slightly longer). The heatsink we're looking at to be 25mm square and top-mounted, which means the fins are facing upward on basically all the PC USB ports I have looked at. The AntMiner U2 heatsink is 25x40mm. If we were doing rear-side heatsinking I could use a full 25x50mm heatsink but I'm not sure how much cooling comes from the bottom on this chip, given Bitmain has zero designs using bottom heatsinking. I don't know if that's because the chip is designed to top-cool, or because of potential ground plane issues with string designs, or both.
If people are concerned about requiring a larger heatsink, I can get a larger heatsink and not change the Compac PCB size, where the extra length of heatsink will be sticking out past the end of the board.

If we end up doing the Amita (the two-chip string) as well, the board will probably have to be wider to accomodate some extra buffer capacitors to help out with node-level core voltage stability. Since I'm planning on just using two Compac heatsinks on the Amita instead of spec'ing a second heatsink, any changes to the heatsink dimension will cause additional changes to the Amita dimension, as the board length will have to accomodate a full heatsink plus as much of a second as doesn't overhang the board.

The total thickness, given that the heatsink will be on the same side as the rest of the parts, should be no more than 14mm. This is PCB thickness plus ASIC thickness plus a small shim plus 10mm heatsink. I figure y'all guys with compact hubs should appreciate this dimension.

so the watts translation for the volts =?
the hash translation for the volts =?

ie:  at the 0.65  volts are we at 2.5 watts and 6gh?

at the 0.80 volts are we at 5 watts and 10 gh?

[sidehack]

You already quoted the answer to your question:

"I'm also going to rig up a USB extension, possibly externally powered, that'll allow me to directly measure input power so we can get some sample efficiency curves off the prototype boards. Since the various modules (right now two PCBs, one of Novak's Prisma adapters and some breadboarding) are basically identical to the Compac as it stands, the power requirements should be pretty close to accurate."

Which is to say, I have not tested this yet but it's on my list for the near term - probably this weekend. Also, the watts and hashes per volt are a whole field of curves dependent on the operating frequency, so there's no simple answer. Once I have the power metering set up I'll probably have to spend a whole day testing different operating voltages at set frequencies (hashrates) to see what's stable and get a series of efficiency curves.

As an initial estimate, I believe the 6GH point I'm at right now should be pulling around 2.1W but I haven't measured that, it's based mostly off theoreticals. Yes, that makes this stick miner more power-efficient than the S5.

[philipma1957]

You already quoted the answer to your question:

"I'm also going to rig up a USB extension, possibly externally powered, that'll allow me to directly measure input power so we can get some sample efficiency curves off the prototype boards. Since the various modules (right now two PCBs, one of Novak's Prisma adapters and some breadboarding) are basically identical to the Compac as it stands, the power requirements should be pretty close to accurate."

Which is to say, I have not tested this yet but it's on my list for the near term - probably this weekend. Also, the watts and hashes per volt are a whole field of curves dependent on the operating frequency, so there's no simple answer. Once I have the power metering set up I'll probably have to spend a whole day testing different operating voltages at set frequencies (hashrates) to see what's stable and get a series of efficiency curves.

As an initial estimate, I believe the 6GH point I'm at right now should be pulling around 2.1W but I haven't measured that, it's based mostly off theoreticals. Yes, that makes this stick miner more power-efficient than the S5.

 

that means it will sell.  I want some please.

[sidehack]

I just finished rebuilding the test regulator for the third time (which makes this iteration number 4) and am about to load-test it. The present design adjusts between 650mV and 800mV and hopefully remains stable at currents above 4A output.

If it behaves well enough, tomorrow I'll look at running it on the hashboard and see about getting some initial W/GH estimates.

Phil, you're on the short list for receiving prototypes to field-test. If the current iteration of the regulator design is good enough, we'll probably be sending off for prototype PCBs early next week and start populating for testing the week after. Which is going to be a pain to do by hand. The bottom half of the board is freakin' dense. In one square inch there's the CP2102 USB/UART chip, a UART level shifter, two LDOs, the oscillator, two LEDs, a couple FETs, and the entire regulator circuit with its approximately two dozen support components. But that's what happens when you build an 8A VRM onto a stick miner for a chip that needs 3 different voltages and takes 1.8V IO and requires a topside heatsink. But we designed the whole thing with nothing smaller than 0603 parts so it's actually possible to do by hand until we can get a decent robot. The worst part will actually be the ASIC itself, since it's a no-leads chip with a belly pad. If there's a hair too much solder on the belly pad (or the VDD corner pads) the thing floats too high and the data pins don't make contact with their pads. So it requires very careful pasting and very precise placement. Which if we don't have good machinery is going to make assembly suck balls, especially on TypeZero boards with a whole bucket of chips.

[quakefiend420]

I just finished rebuilding the test regulator for the third time (which makes this iteration number 4) and am about to load-test it. The present design adjusts between 650mV and 800mV and hopefully remains stable at currents above 4A output.

If it behaves well enough, tomorrow I'll look at running it on the hashboard and see about getting some initial W/GH estimates.

Phil, you're on the short list for receiving prototypes to field-test. If the current iteration of the regulator design is good enough, we'll probably be sending off for prototype PCBs early next week and start populating for testing the week after. Which is going to be a pain to do by hand. The bottom half of the board is freakin' dense. In one square inch there's the CP2102 USB/UART chip, a UART level shifter, two LDOs, the oscillator, two LEDs, a couple FETs, and the entire regulator circuit with its approximately two dozen support components. But that's what happens when you build an 8A VRM onto a stick miner for a chip that needs 3 different voltages and takes 1.8V IO and requires a topside heatsink. But we designed the whole thing with nothing smaller than 0603 parts so it's actually possible to do by hand until we can get a decent robot. The worst part will actually be the ASIC itself, since it's a no-leads chip with a belly pad. If there's a hair too much solder on the belly pad (or the VDD corner pads) the thing floats too high and the data pins don't make contact with their pads. So it requires very careful pasting and very precise placement. Which if we don't have good machinery is going to make assembly suck balls, especially on TypeZero boards with a whole bucket of chips.

I'd be happy to help test a miner as well if you need additional field testers.

[valkir]

Let me know if you want me to test one usb proto board! 

[sidehack]

So, the new regulator iteration has been tested to its limit. I did get over 5A out of it at several tested voltage setpoints, but that's still not really great. I'm hoping when it's mounted on a proper board with better heat dissipation it doesn't wig out quite as much.

Here's a chart of actual regulator performance. The current output is an estimate based off using low fixed resistance loads and not directly measuring current, so the actual current (and therefore actual efficiency) could be skewed, even though I was using 1% tolerance resistors. Wiring and solder joins can have a large effect on overall resistance when the overall resistance is pretty low to begin with.



And now, the fun parts. Based on the current outputs and measured regulator efficiency at various voltages, and extrapolating from Bitmain's efficiency and performance charts for the BM1384, here's some expected performance data on the Compac.





Looks to me like 7GH off a standard 2.5W USB port is attainable at 675mV. The regulator as designed should give us 650mV as a lowerbound, but I had to approximate some of the component values for this test which has shifted the feedback slightly high. It's actually higher than I'd estimated (675mV versus an expected 660mV) but that's not terribly surprising. At 650mV, if the chip'll even start (should, but no guarantees) 8GH should be possible from a stock USB power. This is, unfortunately, not taking into account the added power consumption of the CP2102, IO and PLL LDOs, and LEDs. This all shouldn't add up to a substantial amount of power, but when the ceiling is 2.5W everything needs to be taken into consideration. But that's a job for another day.

[AJRGale]

P0RN! YESH!

when you're done soldering, burning, drilling and popping smoke out of it, i might have to consider buying that toy off you...

I typically eat 3 cheeseburgers, 5 hashbrowns and between 6 and 8 glasses of tea.

it been many years since i've had a cheeseburger, i blame the local maccas and the 14yo's that "like, have better things to do and like, stuff" they have hired. (try ordering a cheeseburger, without any cheese, you'll get my picture)

as for the technical stuff, them there some purty lines you gots there on them pictures!