15 replies
6h38m
Friendly reminder that USB is not free.
You must pay a one-time fee of $6,000 in exchange Vendor ID [0].
6 replies
5h49m
Are there any development boards with USB 3 support? I'm trying to prototype a USB C monitor sink but having trouble finding a board that has the power necessary to receive DisplayPort over USB.
2 replies
5h22m
There is this: https://octopart.com/cyusb3kit-003-cypress+semiconductor-494... and the pricing seems reasonable. When I looked for something like that two years ago the prices were order of magnitude higher.
1 replies
4h38m
This device is not really suited, it is a high speed USB3.0 peripheral. You might be able to use it with the right software, but then you are just using the CPU in it.
0 replies
3h15m
The way how the Cypress FX series works (and for that matter majority of non-trivial USB-to-something chips do) is that there is a bunch of DMA-capable peripherals inside and the in fact ridiculously underpowered CPU core inside only sets up the required configuration for the DMA transactions to happen.
1 replies
3h15m
Most FPGAs with transceivers can do it.
0 replies
20m
Do you have an example? Looking for a product recommendation others have good experience with
0 replies
5h1m
There is not much power needed to receive DisplayPort over USB (assuming you already can receive displayport signals or just route them to an external monitor).
You just need to implement an USB billboard device (optional to make it work, but required by the spec IIRC) and signal the correct alternate function. Then DisplayPort signalling will be present on the USB-C plug. Then just connect the right AUX wires to the DisplayPort connector.
5 replies
4h8m
OK, dumb question, but since we're talking USB on STM32: Does anyone know how to support receiving more than 64 bytes in a frame? I've been looping over 64 byte frames in software, but I know it's possible to go higher. (Up to 1Mbyte I think). The problem is, the Reference Manual lists settings for this that are not normal registers. They are a pseudo-register of some sort. Wondering if there is an easy workaround for this! (The non-OTG USB peripheral)
4 replies
1h31m
USB full speed bulk transfer is limited to 64 bytes. (Dunno which stm32 you're talking about, but stm32g4 is only full speed.)
2 replies
1h4m
A single BULK USB endpoint can only support 64 bytes per transfer. You could make use of multiple endpoints (8 are available in total) or switch to isochronous endpoints which can support up to 1023 bytes per frame.
Most hardware support for isochronous transfers requires DMA on the MCU side, so it tends to be a pain unless your vendor has a library that handles it for you.
You can in general send up to 19 bulk transfers in a single frame (even on a single endpoint), but again, vendor libraries differ wildly in their support for this.
1 replies
19m
Note that isochronous transfers require kernel-mode drivers on the host side, so you won't be able to use libusb in that case. Bulk transfers are the way to go if you want high throughput.
0 replies
7m
Isn't the restriction just on the reception side? So, if you have a MCU talking to a PC or another MCU, you can send however many bytes you want, but not receive? I say this because A: The Reference Manual only indicates this limit for reception, and B: I only experienced this on reception: PCs seem capable of sending and receiving messages larger than 64-bytes, and STM32s seem capable of sending messages larger than 64-bytes, but not receiving (without isosynchronous, or anything special)
0 replies
52m
G4 indeed! I think something in the RM implied it could go higher, but I had trouble interpreting it. Thanks for the explanation.
4 replies
8h14m
Very cool guide.
But if you are worried about soldering more fiddly stuff like those ARM processors: It doesn't have to be that big, STM32 is nice if you need the power, but for smaller stuff smaller controllers can be preferrable.
E.g. one may also consider using VUSB, which is a library that bit-bangs USB on small Atmel microcontrollers: https://www.obdev.at/products/vusb/index.html Example board schematic we've used to teach students Linux kernel module programming: https://gitlab.cs.fau.de/i4/passt/passtboard-v2 with firmware http://www.poempelfox.de/ds1820tousb/ and https://gitlab.cs.fau.de/i4/passt/ds1820tousb
Also very easy, if you are inclined towards Arduino style programming there are tons of boards you can just use as USB devices with the included libraries in very few lines of code, for example https://www.az-delivery.de/en/products/digispark-board
2 replies
7h57m
There's also things like the CH32V203 [1] which is a TSSOP-20 with hardware USB and costs around $0.81 in singles. The software side might be a little more ... challenging, though.
0 replies
6h27m
Software USB can also be done on the 10 cents CH32V003:
0 replies
7h44m
CH32F series is more or less the same and actually has CoreSight SWD and clone STM peripherals
0 replies
7h56m
> if you are worried about soldering more fiddly stuff like those ARM processors
If soldering's a worry, you can get quite reasonably priced dev boards with the microcontroller USB port already fitted and working - such as the NUCLEO-F429ZI https://www.st.com/en/evaluation-tools/nucleo-f429zi.html
Very similar to the NUCLEO-F103RB board the post author used, but as well as the USB connector at the top of the board for the built in programmer/debugger, it also has one at the bottom of the board, wired straight to the microcontroller.
You can also download the board's schematics, if you want to copy their choice of ESD protection and suchlike.
3 replies
8h19m
A very nice writeup and intro into USB, although - it's very focused on using an ST microcontroller, which is a lot more steps and toolchains compared the the recent ESP32 ecosystem that offers a number of easy plug-and-play ways to make USB devices work (for example, several projects from Adafruit's learning pages provide basic use cases). Another issue is differential pairs - having designed several working USB boards myself, this has not a concern for beginners, mainly relevant for doing high-speed work. USB controller ICs (as used typically with arduio/esp) can handle a lot of the details for you, so doing the calculations seems overkill, especially for someone making their first gadget.
0 replies
6h56m
I recently built a small hand-wired macro pad using an Arduino Pro Micro equipped with ATmega32U4, it's apparently quite popular amongst hobbyists building custom keyboards. Quick and fun project for a beginner, the most tedious part of this project was to carve the wooden case.
0 replies
8h3m
I think it is nice to have a basic understanding of differential pairs and impedance, I will admit I never really had to do the calculations since the ecad software I use has several tools for routing differential pairs and even analyzing signals for impedance. But as long as you keep your traces really short it normally doesn't matter.
0 replies
4h24m
USB controller ICs (as used typically with arduio/esp) can handle a lot of the details for you
Can anyone recommend any good USB controller ICs? I normally just use a microcontroller with USB built in.
1 replies
4h21m
A note on USB-C, to augment the article's note: Wire the CC pins to appropriate resistors, or it probably won't work!
And a note on the differential routing and impedance: For USB 2.0, it's not a big deal. Keep the traces of similar length, and reasonably direct. Probably next to each other. You probably don't need to worry about fine-tuning the length and trace widths, impedance control, RF best practices etc. Just connect the nets.
0 replies
1h10m
480MBit/s is fast enough that you do need to worry about best practices and impedance matching within 10% or so. Many MCUs will also need series resistors between the USB PHY pins and the connector.
Will you need to respin a board because you needed to use a 20 mil trace instead of 24 mil? Probably not. All things considered, laying out a USB 2.0 differential pair is pretty low stakes. But you should still try and do it right - it's good practice.
1 replies
3h37m
I've been using https://github.com/xairy/raw-gadget to create a virtual USB device on my raspberry pi I've got plugged into my PC. I'm currently using It to emulate a MTP camera so I can spoof some proprietary software.
0 replies
1h35m
You gotta give us more details than that! Sounds like fun!
1 replies
4h15m
what about converting existing devices from USB-A to USB-C? I have a bunch of powerbanks lying around that I'd love to keep using but most of my devices now use a USB-C charging cable, would it be a simple case of replacing the ports and re-soldering or is there any extra component I need to add?
0 replies
4h12m
I would use an adapter for that use case.
The wiring of the ports on a new design is straightforward; you are using the same pins if it's USB 2.0 (As the article says), plus two extra connections that go to a resistors. If you can find ports that use the same footprint, feasible, but probably not worth it. Desoldering a port is a pain because you have to get all the pins to melting temperature concurrently, and you'd have to figure out how to wire those CC pins.
0 replies
5h45m
fwiw; I've prototyped some USB gadgets using Raspberry Pi Zeroes and Composite USB in the Linux Kernel. At least storage and serial devices were pretty easy to get going.
You'll need something like a shell script on the Raspberry to initialize the composite kernel module and you'll find the boildplate in the kernel docs.
0 replies
26m
I used to test devices for USB compliance a long time ago. One of the things I often saw problems with was the inrush current test. Basically too much bypass caps on the 5v. I didn't see it mentioned in the article. It's really easy to get focused on the high speed digital design but for compliance it's sometimes the less sexy stuff that gets you. No idea how this stuff works with newer versions of the standard but it seems like there still is a test. Nice article though.
https://compliance.usb.org/index.asp?UpdateFile=Electrical#:....
0 replies
8h6m
This is a very well written and informative article for working with USB, wish I had it when I first started USB signals.
0 replies
7h54m
I recently used CH340N (soic 8 virtual com port) and it was really easy. Easy soldering, no extra parts just directly connect to USB, works out of the box on Linux.
0 replies
2h59m
I use ESP32 mostly but I have a cheap hack that fits a lot of projects...
For super quick easy custom controllers, also consider pulling the control board from discarded USB keyboards. Use conductive glue instead of solder to attach wires to the contacts, and a helping of hot glue to keep them secured. I've made cheap but very robust 1-button game controllers with an arcade button that sends a space bar click. You get all the debounce etc, no code.
Wow, first time I hear about it, this is an eye opening experience.
I will think twice now before saying “why couldn’t they just use USB for this?”
I dunno, I think either you're doing a small run and you can just bake in a Teensy or whatever, or you're doing a big run and $6k is a drop in the bucket.
Even crazier, it's just a 16 bit value.
What are they gonna do when they run out?
.. or use someone else's. I believe there's a hobbyist VID under which you can reserve PIDs, or in many cases you can just copy an existing product if your device is generic enough and you're not planning to sell a big production run.
There's pid.codes which uses a vid of a defunct organization, but before that there was also the F055 vid. I still use that vid because no company will accept that vid, since it's commonly used by foss projects.
The part that makes me feel most uncomfortable about usb VID/PIDs is that they are only 16bits each. While I don't think 4billion unique commercial USB devices is limit we will reach anytime soon, efficiently managing the available address space is a different question. And unlike IPv4 addresses a range of USB VID/PIDs can't be as easily reused without making the VID/PID meaningless.
By that time they'll just add an extra field to the protocol and assign a special "see other field" VID/PID pair.
For a lot of products the VID/PID combo isn't that important on a protocol level, and there's technically no reason why two completely unrelated products couldn't be using the same pair. In practice you're mainly going to use them for software to target a specific device, for example the Linux HID driver uses it to work around hardware/firmware bugs. But HID devices are self-describing, and that's the main mechanism used by the driver to figure out what has been attached and how to behave.
If modern OSes can do the same to distinguish hardware with the extra field, sharing the same value for backwards compatibility with legacy machines really isn't going to be a big deal. It's not like MAC or IPv4 addresses where a clash will essentially kill all communication.
See also https://pid.codes/
For the DirtyJTAG project we use one of those:
https://pid.codes/1209/C0CA/
I’ve commonly seen OpenMoko’s ID, 1d50, used for free projects. See the list at <http://www.linux-usb.org/usb.ids>.
Yeah, I was going to ask about this. I think ST Micro will sublicense you a PID under their VID, but with restrictions, and companies attempting to buy a VID and sell PIDs as a service have been sued?
NXP runs a USB VID/PID Program [0] for small production designs (<10,000 units) that use their MCUs. They’ll give you 3 PIDs for free under one of their VIDs. I use this in my side projects (~200 units) and works pretty well!
[0] https://community.nxp.com/t5/Kinetis-Microcontrollers/NXP-US...
Many chip vendors will give you a PID under their VID if you're making a product. For example this blog post uses and ST chip, and they'll provide a PID if you request it [1] - free of charge, but subject to some conditions.
(Of course if your USB device needs Windows drivers, you'll still have to deal with things like code signing...)
[1] https://community.st.com/t5/stm32-mcus-embedded-software/dea...
I just use 0xF055 as VID. What is the USB-IF gonna do?
For hobbyist use you can just pick a random value and it'll usually work. Open-source hardware can get a product ID for free from https://pid.codes. Small-run commercial hardware can usually get a free product ID from the maker of their USB-capable chip. And once you're big enough that you're designing your own chip, $6,000 isn't such a big deal anymore.
So yes, you are technically right, but it really doesn't matter all that much in practice. USB is by far one of the most accessible major hardware standards out there.
FWIW, for my own personal projects I resort to vendor id 6666 (Prototype).