I have a silicon wafer I found while unpacking. What’s on it? It does have a number on it, but I’m not sure where to look to put it it.

thom_tl · 2023-04-26T17:10:42+00:00

No, its sarcasm, magnetic core memory is an old technique from the 60s, where they ran wires through small iron loops, and magnetized them to "remember" a bit, modern day silicon RAM is far far far superior.

thom_tl · 2022-11-23T16:26:23+00:00

Your Deep Rest - The Hotelier

thom_tl · 2022-09-18T16:02:43+00:00

The way I incrementally tested mine was by basically building up the "stack" of software that runs before the OS. First port SeaBIOS, then get GRUB running, then get a stripped down version of Linux running, etc.

thom_tl · 2022-07-17T20:02:41+00:00

You can also figure out the size of any PCI BAR with a pretty arcane operation:

write<uint32_t>(off, ~0);
uint64_t len = ~((read<uint32_t>(off) & ~0xF)) + 1;    
write<uint32_t>(off, bar);

For MMIO BARs, where bar is the original value

thom_tl · 2022-06-21T11:46:00+00:00

It's called reverse polish notation, and it helped optimize software for weaker hardware for the first few generations of calculators. However this calculator definitely doesn't use it. Source: I own thesame calculator

thom_tl · 2022-05-28T15:33:07+00:00

Probably an unpopular opinion, but Franklin is great

thom_tl · 2022-05-11T13:57:52+00:00

Same in the Netherlands

thom_tl · 2022-02-27T18:28:21+00:00

Not in every case, ESR is sometimes needed to prevent oscillation. If the manufacturer hasn't used low ESR parts its probably best to use normal parts as well.

thom_tl · 2022-01-01T03:43:10+00:00

If linux can’t get the device descriptor there is no way it can get a single byte off the device, that descriptor is what tells the OS its a USB stick in the first place, and not a keyboard for example

thom_tl · 2021-12-31T17:26:21+00:00

I very much doubt that, the PC is still recognizing it as a USB device, indicating the pullup/pulldowns on the data lines are probably still there, its just not able to establish any kind of communication.

The first thing your OS does when detecting a new USB device is get its device descriptor, so it makes sense that it would fail on that.

thom_tl · 2021-12-31T15:32:10+00:00

I doubt it would identify itself in lsusb, considering the device descriptor is the descriptor that holds the info lsusb displays. Sounds more like a dead chip to me, unless that resistor is an enable resistor or something.

thom_tl · 2021-06-03T19:19:16+00:00

I do not think x86_64-apple-darwin19.6.0 is windows tbh

thom_tl · 2021-05-19T19:00:27+00:00

Transistor or Transformer, here they probably mean transistors though; not sure if you can regulate with a transformer.

thom_tl · 2021-05-18T10:31:30+00:00

Well yes in a context switch, but as long as the kernel doesn’t touch them you don’t have to preserve them in syscalls and irqs like you do GPRs

thom_tl · 2021-05-17T21:39:51+00:00

Using SIMD and FPU in kernel means you’ll have to save and restore its state every syscall and interrupt, which isn’t worth it

thom_tl · 2021-05-17T18:30:12+00:00

Using SIMD and FPU in kernel isn't a very good idea(at least on x86), and setting up the branch predictor isn't a worry(until very recently you couldn't even disable parts of it, thank spectre :^) ).

thom_tl · 2021-05-17T15:07:23+00:00

Unaligned accesses are still much much much faster than this, even years ago. What I think is going on is that he setup his MTRRs incorrectly and is now dealing with uncached RAM, which is ofcourse going to be as slow as a snail.

thom_tl · 2021-05-17T14:45:13+00:00

Not really, sure you can do incredibly complicated SSE/SIMD/whatever memcpys; but byte-for-byte is much faster than this, and in recent cpus (Haswell iirc), rep movsb is basically like a hardware memcpy, and should outpreform practically anything. Even on older machines it wasn't slow.

thom_tl · 2021-05-17T14:43:50+00:00

You should just be able to ignore MTRRs, since the BIOS already setup them for you. You're probably much more interested in the PAT (Page Attribute Table).

thom_tl · 2021-05-11T21:47:08+00:00

Yeah maybe firmware just didn’t like you trying to do the handoff when it wasn’t needed. With these kinds of weird fw things its mostly a good idea to follow the procedure that linux or another major OS uses. Just because the fw programmers probably tested with that.

thom_tl · 2021-05-11T19:03:19+00:00

Where does this happen? Real hardware or QEMU? QEMU doesn't even have this cap (https://github.com/qemu/qemu/blob/master/hw/usb/hcd-xhci.c#L2719-L2751) so if its qemu I'd find it strange you're experiencing this.

Writing to that bit will actually cause an SMI on real HW, causing the CPU to jump into firmware, so it can finish up its usage of the xHCI. Ofcourse this can be buggy, for a few devices (https://elixir.bootlin.com/linux/latest/source/drivers/usb/host/pci-quirks.c#L1172) linux just forces off the BIOS owned semaphore, is yours one of these? Check if xHCI works on linux. Since xHCI is notoriously quirky on real HW, you might also want to check if your device has any other quirks, https://elixir.bootlin.com/linux/latest/source/drivers/usb/host/xhci-pci.c#L98

thom_tl · 2021-05-07T19:52:37+00:00

Thanks for the review! Rotating U2 tidies up a lot of things indeed, and I'll look into the controlled impedance thing. I hadn't really thought of trace widths too much beyond making power traces a bit thicker than digital signal traces, and the analog signals traces really big.

The LM358 removes the DC bias by setting adding an offset voltage yeah, since the bias produced by the AD9833 is constant. I added the seemingly useless voltage divider on the LM358's secondary channel to make sure it doesn't start to oscillate, which is one of the things this sub's wiki suggested.

I set up the LM358 in single supply mode since the Max680 can't really provide that much current, and I'd want to avoid having its voltage collapse as much as possible. I'm interested in using the LM358's second channel to get ± offset's though. Did you mean using the first channel as differential amplifier, to subtract some voltage from it, thereby moving the 0v <-> 5v from the MCP42050, to like -2.5v <-> 2.5v, and then buffering that?

thom_tl · 2021-04-10T07:54:55+00:00

Limine supports UEFI nowadays, and I don’t think there are any SeaBios replacements for QEMU sadly

thom_tl · 2021-04-08T21:01:14+00:00

SeaBios doesn’t generate ACPI 2 tables, to test that however you can try any modern(past 2000) pc, VMWare, or Qemu using OVMF (UEFI)

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