LMARV-1 reboot part 11: The crossbar

Here's the "crossbar", which is a generic card which takes N 32-bit inputs, multiplexes them, and is either registered or buffered on the output. The sequencer will need eight of these crossbars, all different.
nMigen exercises: github.com/RobertBaruch/nmige...
github repo for code: github.com/RobertBaruch/riscv...
RISC-V specs: riscv.org/technical/specifica...
nMigen tutorial: github.com/RobertBaruch/nmige...

[@KireTheCat]

*casually has dragon head on*

[@gsuberland]

"this is a schematic" no it's not it's a dragon

[@xxleite]

nice furry electronics intro :D

[@veontube]

I remember this thing, that "happened".

[@stuckinpants]

Removal force will be huge, put some holes near the top so you can add handles or just to get an L wrench in.

[@RobertBaruch]

That's probably a good idea, even if I don't need it. Because what if I do? :)

[@gsuberland]

If you put mounting holes in your board and on your breakout test board, aligned at the same position, you can use slotted L-brackets and some small nuts and bolts to hold them in position while you solder. The slots mean you don't need to get the X/Y/Z alignment perfect ahead of time. A dollar worth of parts saves you manually holding the board upright.

[@RobertBaruch]

That's an interesting idea! I was going to be lazy and just hope, but maybe I can just 3D print some brackets/slots. I'm enthusiastic!

[@gsuberland]

@@RobertBaruch 3D printed also works, if it's worth your time!

[@JG-nm9zk]

Just started using kicad after watching your videos. Ordered my first board the other day. 🍻 to them turning out alright

[@grobble]

I'm not sure you shift the mtvec by 2 bits to get the address, as instructions are 4 byte aligned. They just use the bottom two bits for the mode and store the address as is. So you gotta mask to get the address (unless that's what you mean)

[@RobertBaruch]

There was a reason... Oh right. The implementation shifts mtvec right by 2, adds the cause, then shifts the result left by 2. This is equivalent to masking off mtvec, multiplying the cause by 4, and adding.

[@marknn3]

I was thinking the exact same thing. From riscv-privileged-v1.9.1.pdf page 28: "The value in the mtvec register must always be aligned on a 4-byte boundary (the low two bits are always zero)"

[@marknn3]

@@RobertBaruch Ah, that makes sense now. It's an implementation detail.

[@truezulu]

Arrgh wtf! Ffs! Hhhhhhhhh You scared me :) Edit: Great stuff as always... Hoping for another live vid ;)

[@HorochovPL]

Problems with card-edge (now I know where does the cartridge word come from) insertion force? Just use hammer.

[@RobertBaruch]

Hammer solve everything.

[@abebarker]

I'm interested to see whether or not your 3.3v to 5v interface is able to handle much speed. I saw a reduce speed or even a complete failure with some noise. Sometimes it helps to have a level converter.

[@tomaszcichocki8281]

When watching I had an idea to overlap elements that won't be used on the same instance of a board. Ie those in a package with connections on sides only. Maybe you could make the board smaller. But that's probably a bad idea. KiCad would shout on you in DRC and you would have hard time when routing :)

[@hxt21]

Can we be allowed to see you make a boards in kicad and talk about singularity. Really enjoy the old risc-v youtub where we saw you make boards

[@RobertBaruch]

I suppose? It could be long and boring...

[@hxt21]

@@RobertBaruch I do not think it's boring, not at all.

[@TomStorey96]

We want to see it all 😄

[@suncrafterspielt9479]

that intro 😂

[@DmiA]

Hello Robert! Please tell me, do you still plan to make available for purchase a replacement lcd for Sharp PC-1245?

[@RobertBaruch]

Soon.

[@furrtek]

Excuse me but DRAGON

[@RobertBaruch]

Derg happen.

[@alessiocaffi5992]

@@RobertBaruch actually resemble the "Goat" from Dante's Inferno, hope I wont have a nightmare, hah joking BTW incredible stuff, hope to see it completed and see videos saying "inspired by R. B. " as many bboard vids on yt. ... back to watching your video. cheers.

[@RobertBaruch]

@@alessiocaffi5992 Oh interesting, I didn't know people were actually being inspired by this. That's good to know!

[@alessiocaffi5992]

@@RobertBaruch I am sure you gonna inspire few of us, but, sorry, not as many as this ,easy to follow, bboard ttl cpu enthusiast (in reality a good series on teaching a SAP-1 by Malvino) cause you are on another planet, maybe in Andromeda. I am an EE and barely can keep up, gotta review nMigen , haaa. greetings. ps. no nightmare.

[@jamesrivettcarnac]

Yay metric!

[@TomStorey96]

You couuullllld use an ATF150xASV CPLD simply because it can be (re)programmed in-circuit via JTAG. If you need to fix something in the GAL once it is soldered to the board, that could be a little bit of a pain.

[@RobertBaruch]

I'm intrigued by the ATF1502ASV. It seems to be sized well, and uses 3v3 power. I'll look into this more, because it is not that much more complex than the 22V10, and could conceivably have its fuse map reverse-engineered.

[@TomStorey96]

@@RobertBaruch I've used the ATF150x CPLDs in a couple of projects, 5V and 3V3 parts. You can write CUPL for them using WinCUPL, or you can use an older version of Altera Quartus that supports the EPM7000 family of devices to write Verilog or VHDL, and then use pof2jed to convert to a format for programming via ATMISP. You just choose the equivalent Altera part in Quartus: EPM7032==ATF1502, EPM7064==ATF1504, EPM7128==ATF1508. Pin for pin compatible.

[@TomStorey96]

ATDH1150USB is the programmer to look for, they are not stupidly priced like Altera's programming tools.

[@RobertBaruch]

@@TomStorey96 Compared to those, this is pretty cheap.

[@dnwheeler]

Who are you and what have you done with Rob?!?

[@RobertBaruch]

I eated it.

[@havresylt]

Looks more like a weird horse to me

[@RobertBaruch]

Well, you're not totally wrong. Horse heads and dragon heads have numerous similar features. On the other hand, horses, even weird ones, usually don't have horns, slit pupils, and fangs :D

[@havresylt]

@@RobertBaruch Aha! Well, maybe horses do where I'm from! At least the weird ones. Anyways, nice video. Looking forward to the next one!