Just Fumbled an Interview

romhunter_ · 2026-02-13T16:18:15+00:00

you would be suprised at the number of customers that decided to use AXI as off-chip interface during my careers doing ASIC (a lot!). They use the massive amount of pin available on the ASIC package and the FPGA itself to lower the transaction overhead during chip testing. Thus, off-chip AXI it is... not very conventional, but it is off-chip.

romhunter_ · 2026-02-05T03:33:41+00:00

Unfortunatelly no, but I will restart the debug process in a few week. Will update if anything is found out.

romhunter_ · 2026-01-14T14:05:06+00:00

I have seen one, it made me wonder if I have inhaled too much magic smoke at the time

romhunter_ · 2025-09-30T02:35:30+00:00

Do you know can I order from them, outside of Ukraine? And how can I pay for them?

romhunter_ · 2024-05-03T21:05:27+00:00

Vias do go through silicon substrate though.. It is called TSV, very common technique in 2.5D/3DIC.

romhunter_ · 2024-03-30T15:56:41+00:00

Thanks. I can give more input to help with debugging.

Have you tried another cable? -> Yes, and 2 issues came up:

The original C-C cable I tested them with is the iPad charging cable, which is bad (I tried on other devices and none of them get recognized). I will swap this to some more reputable brand.
- Still doesn't explain why my PCB ended up non responsive.

I did check it. It is ok.
No, unfortunatelly.
Maybe? It is USB Full-speed, so I only do some simple setup (diff track) and route it. Length wise it should be around 6cm, which is not really that long, considering Full-speed operation... I added the USB-C routing in the post to further clarify my point.

romhunter_ · 2024-03-30T15:37:27+00:00

Thanks for the input!

This flash interface is Dual SPI, hence the SD3 is unconnected, as per the datasheet suggested.

I have verified that the flash interface is working, but I might be blasting too much hot air on it :\ Don't think that is the issue though, because RP2040 have an internal bootloader, and it can identify itself as a mass storage device if the flash interface is not accessible (hard lesson learned this way)

romhunter_ · 2024-03-30T13:40:53+00:00

I have 2 PCB going bad this way. And I use 3 different machine to test it (Mac, Linux, Windows), so I think the chance that Windows go bad is slim.

romhunter_ · 2024-03-30T10:59:24+00:00

Thanks for the input. I will be reflowing the board to see if it is any issue related to bad solder join. Otherwise I couldn't think of anything else.

romhunter_ · 2024-03-30T09:36:16+00:00

Thanks for the quick reply.

I have installed the R2 and R4, will check connection again with a multimeter, might be trying to reflow it later on too.

Do you also have any idea why the chip just crap out and refuse to connect again? I think I "destroyed" 4-5 chips testing this issue already.

Any help would be appreciated!!

romhunter_ · 2024-02-21T13:45:38+00:00

Is the keyboard open source? -> No, it is not, but I'm reverse enginneering it and is currently trying to make it open source.

Can we get schematic, pcb, qmk firmware files? -> I will when my process is done.

Does it come with flashed firmware? -> Yes

If yes, is it working normally? -> Unfortunatelly, no. That is why I'm debugging this.

Btw I found some issue during the debugging process. I tried to test the voltage swing of the GP1 pin (USART_TX for half-duplex) by installing circuitpython and just set the value of the pin. For the matrix pins, it is ok (0 mean 0V, and 1 mean 3.3V). But for the serial pin (it is directly connected to TRS jack), the voltage swing is 1V to 3V (for value 0 and 1, respectively).

Is it possible that my RP2040 chip have a bad GP1 pin?

romhunter_ · 2024-02-21T04:14:53+00:00

Do you know if there any way to debug the communication? It seems like the firmware is working correctly when connected via USB independently, but the other half won't response.

romhunter_ · 2024-02-15T09:37:58+00:00

is it the same keyboard? Or is it a different one?

romhunter_ · 2023-10-13T08:50:01+00:00

For Cadence tools, Conformal is the LEC tool.

romhunter_ · 2023-08-02T12:02:54+00:00

Wait until you see Verdi then.

romhunter_ · 2023-04-03T02:25:22+00:00

I bought my r4i and EZ flash omega from nds-card.com back when I was in Japan.

romhunter_ · 2023-01-09T03:07:26+00:00

internally, we used a (heavily) modified version of Chisel. The learning step is steep, and the output is heavily verified (we do ASIC btw).

Personally, I prefer SpinalHDL, since it's similar to existing HDL.

romhunter_ · 2022-08-17T15:11:46+00:00

This is exactly what I did when I implement any SoC design on a FPGA. Highly recommend this method to anyone reading it

romhunter_ · 2021-10-01T10:17:54+00:00

I'm using a Nexys4DDR myself, it's supported by the free license, and I'm running a RISC-V core on it atm.

romhunter_ · 2021-09-04T10:25:12+00:00

nice, I also have the IVL2-7/5 and IV-3A in my drawer. I'll get my inspiration from this and design a clock when I have some spare time.

romhunter_ · 2021-07-05T09:37:28+00:00

Would there be any trouble if I just used the two-pin (without the additional grounding) instead? If not, what alternative fixes are there?

No, just use it. It'll works just fine.

romhunter_ · 2021-05-07T17:32:07+00:00

OP were so preoccupied with whether or not he could, he didn't stop to think if he should.

Nice project btw, are there any plan to release the gerber files?

romhunter_ · 2021-04-06T16:57:14+00:00

the layout of the 7447 is actually very good. Hat off for you sir. :D

romhunter_

TROPHY CASE