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azonenberg, 9 days ago to random

My dream laptop:

• Form factor of a late 90s / early 2000s (1.5-2" thick, 15" screen size or so) laptop. None of this thin-and-light nonsense.
• Sunlight readable display capable of being used in reflective (backlight off) mode for reduced power
• Optional cellular modem module
• Two (or more) externally accessible, hot-swappable 100Wh batteries with power ORing. If you're going on a plane you can take some of the batteries out to make the FAA happy. But if I'm on the road I want the option to have several batteries and swap them without needing to be plugged in or shut down. The goal is to support multiple days of off-grid usage with no charging access.
• 1000baseT and 10G SFP+ Ethernet ports
• Lots of USB A and C ports. 5-10, at least, spread across several roots for improved bandwidth
• Modular, repairable, upgradeable design so I can e.g. swap out the CPU board when it becomes obsolete but keep all of the peripherals and chassis

azonenberg, 17 days ago to random

How crazy/horrible/stupid would it be to write a single-pass streaming parser for ELF as part of a firmware updater?

More specifically, you're given a chance to look at each byte of data once. You can either write it to flash immediately, update some local variables (like "offset of .text"), or ignore it.

But once you've seen a given part of the file, you can't rewind and look at it again later (since I'm flashing an image that might be larger than available RAM).

How likely is this to fail in practice? I'm not asking if one of the POC||GTFO editors could craft an ELF that would break this, I'm sure they could. But if I control the linker script generating the file, and have the parser simply refuse to process any file that doesn't play by my rules, am I probably OK?

azonenberg, 23 days ago to random

New thread on my big ongoing embedded project since the other one was getting too big.

To recap, this is a pilot project for a bunch of my future open hardware T&M and networking projects, validating a common platform that a lot of the future stuff is going to run on.

The primary problem it's trying to address is that I have a lot of instrumentation with trigger in/out ports, sometimes at different voltage levels, and I don't always have the same instrument sourcing the trigger every time.

So rather than moving around cables all the time and adding splitters, attenuators, amplifiers, etc. to the trigger signals I decided to make a dedicated device using an old XC7K70T-2FBG484 I had lying around.

Of course, as with any project, there was feature creep.

I'm standardizing on +48V DC for powering all of my future projects as it's high enough to move a lot of power but low enough to be mostly safe to work around live. So I needed to design and validate an intermediate bus converter to bring the 48 down to something like 12 for the rest of the system to use.

The FPGA has four 10G transceiver pairs on it. I used one for 10GbE (not that I need the bandwidth, but I was low on RJ45 ports on this bench and had some free SFP drops) and the rest are hooked up to front panel SMA ports (awaiting cables to go from PCB to panel) to generate PRBSes for instrument deskew.

Since I'm pinning out the transceivers and am planning to build a BERT eventually, I added BERT functionality to the firmware as well (still need to finish a few things but it's mostly usable now).

And since I have transceivers and access to all of the scope triggers, it would be dumb not to build a CDR trigger mode as well. That's in progress.

azonenberg, 1 month ago to random

Anybody know the typical flow rate (in SCCM or similar volume flow units) and discharge pressure for duster gas cans?

Looking at replacing my current HFO-1234ze cans with N2 for most applications for cost/environmental reasons but trying to figure out how much I'll actually go through and what size regulator I should get (the one I currently have on my N2 tank is meant for very low volume inerting and tops out at 30psi which is likely too low).

azonenberg, 1 month ago to random

Dream MCU wishlist item 732: Simple, high-speed serial protocol for fast memory mapped point-to-point IO.

Basically "PCIe lite". 8b/10b coded ~1 Gbps full duplex LVDS with packetized memory read/write requests bridged directly to AHB on the MCU side.

But no PnP enumeration, no device addressing, no request reordering, none of the other complexity of full PCIe. Something you can hang off a Cortex-M7 and use for interfacing to a lower end FPGA faster than QSPI.

azonenberg, 2 months ago to random

Assembling the trigger crossbar board over lunch.

Not thrilled with the paste print quality, very inconsistent. the top left corner was way too thick as the board flexed during printing, the middle BGA skipped some pads, and the WLCSP in the bottom right was near perfect.

These big boards bend too much in my paste fixture, I need to find a way to prevent that before I do any more boards of this scale.

azonenberg, 2 months ago to random

So this is interesting and annoying.

I've been having intermittent breaker trips on circuit #18 in my lab. The receptacles in this circuit are mostly behind cabinets, the only one in use powers an LED strip in my components cabinet. The last time the breaker popped I unplugged the LED strip (leaving the circuit, in theory, completely unloaded) and a few days later when I checked the panel again it had tripped.

Today I had a bit of downtime and decided to investigate. With the breaker locked out in the panel and the feed line coming out of the cable tray removed at the first splice I verified hot to ground, hot to neutral, and neutral to ground all measured off scale high (>2200M ohms) on a Fluke 1503 with 1 kV test voltage.

Which pretty much rules out a wiring fault in the wall. This is the same test I did before commissioning the wiring and it passed at that time with the same result.

azonenberg, 2 months ago to random

Random thought while assembling a PCB: Has there ever been a literal SHTF situation? As in, fecal matter impacting a rotating air circulation device?

How would such a situation arise, considering that plumbing and HVAC are (normally) kept quite separate from one another?

azonenberg, 3 months ago to random

Does ST (or anyone really, but ideally a STM32 variant) have any Cortex-M based MCUs with multiple IO banks and separate VCCIO for each?

I find I need e.g. 3.3V and 1.8V GPIOs in a lot of applications and I have to throw external level shifters or a CPLD or something onto the board.

Would be handy if the micro could just run a couple of IO ports at a different voltage level.