So, the initial, and real reason that NKRO was introduced was to deal with inexpensive keyboards that used grid encoders. This requires that each key be assigned a place on a grid, with each row and column having a wire associated with it. When you push a key, it sends the associated pair of wires high voltage. The keyboard encoder chip has those wires running to its pins.
Such a scheme can permit detecting any one key going down, which will always set two wires to high voltage. It can permit detecting any two keys going down, since that will always set at least one more line to high voltage, which will uniquely identify the key. But beyond that, additional keys may not be possible to uniquely identify (and, in fact, pushing one may send only lines that are already high to high, which is totally invisible to the encoder), and so it may ignore additional keys.
This prevents a grid-based encoder from doing NKRO.
If you want to do NKRO, you have to have a unique line coming from every keyswitch, which costs money.
There is a second issue with NKRO.
You can have a keyboard that can have NKRO to the encoder, rather than a grid. And can have a USB interface to talk to the computer.
But last I looked, USB has a protocol limitation that cannot support NKRO, and this was a major reason that you could still get some dual-interface keyboards with PS/2 support and USB recently.
PS/2 is edge-triggered by a key. A key goes down, the computer gets a message. A key goes up, the computer gets a message. All that message says is “this key went down” or “this key went up”. The computer maintains a list of keys and its idea of the up or down state of them.
This is also why PS/2 keyboards can sometimes have keys that appear to be “stuck” that get unstuck when you tap them — if the computer misses the “up” message for some reason, then it only gets notified about it next time the key changes state and the computer gets a message about it.
USB doesn’t work like that. When a USB keyboard sends an event, it contains a dump of the keyboard state. Every keypress, new dump. However, there’s a restriction on the size of the message. It can only contain…I think it’s seven keys that are down, plus modifier keys.
kagis
Six keys.
In practice, six is probably enough for pretty much anyone. The real problem was grid encoders, as a video game player might legitimately hit three or four keys at once. But…it still isn’t, strictly-speaking, NKRO unless it can do all.
It looks like there are basically two approaches that keyboards have used to try to provide a similar effect. One is to just invent a proprietary protocol, and rely on that and a driver rather than the standard USB keyboard behavior.
The other is to tell the computer that the keyboard is a whole array of keyboards. Since most OS environments can use multiple keyboards and just use their input, such a keyboard can pretend to have multiple keyboards pressing buttons.
You’re describing the boot keyboard, not the full USB HID protocol. It is true that there are some keyboards that only support NKRO, but the USB HID protocol has supported NKRO forever. https://www.devever.net/~hl/usbnkro
Per this thread from 2009, the limit was conditional upon using a particular keyboard descriptor documented elsewhere in the spec, but keyboards are not required to use that descriptor.
I tested just now on one of my mechanical keyboards, on MacOS, connected via USB C, using the Online Key Rollover Test, and was able to get 44 keys registered at the same time.
I also checked my Iris and Moonlander - both cap out at 6, but I believe I can update that to be higher with QMK or add a config key via Oryx on the Moonlander to turn it on.
I don’t know about AM5, but I’m running a 5700X3D on a motherboard that still has a PS/2 port. (Not that I’m using it, but it’s there.) You can still have a pretty modern system with PS/2 if you really want it.
Mine is a B350 – I’m still running the same motherboard I used 7 years ago with my old Ryzen 1700X. Considering how much depends on the CPU these days instead of the chipset, does it even really matter if the chipset is older?
Chipset itself doesn’t matter, it it dates the board.
On AM4 basically every board has it. Maybe the really dire boards would skit it, but they’re skipping so much more first. Starting with early AM5 (6XX) and it actually started disappearing and now with 8XX it’s getting much less popular.
Also how’s your B350 board holding up? My X370 board died after about 3.5 years, and my friends X370 had been acting up after about 5. Maybe the higher end chipsets are cursed? I sure hope my new board lasts because I paid a fuck ton for it.
Just fine so far, but thanks a lot for jinxing it! 😠
It’s a Gigabyte AB350N-Gaming WiFi, which is a mini-ITX board, so having the B-series chipset was probably less about making it cheap and more about the features of fancier chipsets being wasted on a board that didn’t have enough space to implement the connectors for them. Therefore, it might like slightly higher quality than some other B350 boards.
PS/2 ports?
Don’t forget the xt/at port
I’m still mad they killed PS/2 on recent motherboards. So much for NKRO I guess.
NKRO is available for USB keyboards too.
Ehhh.
So, the initial, and real reason that NKRO was introduced was to deal with inexpensive keyboards that used grid encoders. This requires that each key be assigned a place on a grid, with each row and column having a wire associated with it. When you push a key, it sends the associated pair of wires high voltage. The keyboard encoder chip has those wires running to its pins.
Such a scheme can permit detecting any one key going down, which will always set two wires to high voltage. It can permit detecting any two keys going down, since that will always set at least one more line to high voltage, which will uniquely identify the key. But beyond that, additional keys may not be possible to uniquely identify (and, in fact, pushing one may send only lines that are already high to high, which is totally invisible to the encoder), and so it may ignore additional keys.
This prevents a grid-based encoder from doing NKRO.
If you want to do NKRO, you have to have a unique line coming from every keyswitch, which costs money.
There is a second issue with NKRO.
You can have a keyboard that can have NKRO to the encoder, rather than a grid. And can have a USB interface to talk to the computer.
But last I looked, USB has a protocol limitation that cannot support NKRO, and this was a major reason that you could still get some dual-interface keyboards with PS/2 support and USB recently.
PS/2 is edge-triggered by a key. A key goes down, the computer gets a message. A key goes up, the computer gets a message. All that message says is “this key went down” or “this key went up”. The computer maintains a list of keys and its idea of the up or down state of them.
This is also why PS/2 keyboards can sometimes have keys that appear to be “stuck” that get unstuck when you tap them — if the computer misses the “up” message for some reason, then it only gets notified about it next time the key changes state and the computer gets a message about it.
USB doesn’t work like that. When a USB keyboard sends an event, it contains a dump of the keyboard state. Every keypress, new dump. However, there’s a restriction on the size of the message. It can only contain…I think it’s seven keys that are down, plus modifier keys.
kagis
Six keys.
In practice, six is probably enough for pretty much anyone. The real problem was grid encoders, as a video game player might legitimately hit three or four keys at once. But…it still isn’t, strictly-speaking, NKRO unless it can do all.
It looks like there are basically two approaches that keyboards have used to try to provide a similar effect. One is to just invent a proprietary protocol, and rely on that and a driver rather than the standard USB keyboard behavior.
The other is to tell the computer that the keyboard is a whole array of keyboards. Since most OS environments can use multiple keyboards and just use their input, such a keyboard can pretend to have multiple keyboards pressing buttons.
You’re describing the boot keyboard, not the full USB HID protocol. It is true that there are some keyboards that only support NKRO, but the USB HID protocol has supported NKRO forever. https://www.devever.net/~hl/usbnkro
Per this thread from 2009, the limit was conditional upon using a particular keyboard descriptor documented elsewhere in the spec, but keyboards are not required to use that descriptor.
I tested just now on one of my mechanical keyboards, on MacOS, connected via USB C, using the Online Key Rollover Test, and was able to get 44 keys registered at the same time.
What keyboard are you using? I have yet to use one that supports more than 6 over USB.
The one I grabbed to test was the ROG Azoth.
I also checked my Iris and Moonlander - both cap out at 6, but I believe I can update that to be higher with QMK or add a config key via Oryx on the Moonlander to turn it on.
deleted by creator
I don’t know about AM5, but I’m running a 5700X3D on a motherboard that still has a PS/2 port. (Not that I’m using it, but it’s there.) You can still have a pretty modern system with PS/2 if you really want it.
X670 tier boards were some of the last to have PS/2. I got an X870 board :(
Mine is a B350 – I’m still running the same motherboard I used 7 years ago with my old Ryzen 1700X. Considering how much depends on the CPU these days instead of the chipset, does it even really matter if the chipset is older?
Chipset itself doesn’t matter, it it dates the board.
On AM4 basically every board has it. Maybe the really dire boards would skit it, but they’re skipping so much more first. Starting with early AM5 (6XX) and it actually started disappearing and now with 8XX it’s getting much less popular.
Also how’s your B350 board holding up? My X370 board died after about 3.5 years, and my friends X370 had been acting up after about 5. Maybe the higher end chipsets are cursed? I sure hope my new board lasts because I paid a fuck ton for it.
Just fine so far, but thanks a lot for jinxing it! 😠
It’s a Gigabyte AB350N-Gaming WiFi, which is a mini-ITX board, so having the B-series chipset was probably less about making it cheap and more about the features of fancier chipsets being wasted on a board that didn’t have enough space to implement the connectors for them. Therefore, it might like slightly higher quality than some other B350 boards.