# Interesting scanner behaviour that I can't explain **URL:** \ **Category:** Kaleidoscope Internals\ **Tags:** question\ **Created:** [January 24, 2018, 7:12pm UTC](https://community.keyboard.io/t/interesting-scanner-behaviour-that-i-cant-explain/950 "2018-01-24T19:12:01Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![merlin](https://yyz1.discourse-cdn.com/flex031/user_avatar/community.keyboard.io/merlin/32/3416_2.png) [@merlin](https://community.keyboard.io/u/merlin)\ **Post date:** [January 24, 2018, 7:12pm UTC](https://community.keyboard.io/t/interesting-scanner-behaviour-that-i-cant-explain/950/1 "2018-01-24T19:12:01Z")
I’m trying to understand some of the behaviour that I’m seeing from Kaleidosocope, and I’m at a loss. I started out by thinking about a keymap with two keys defined as `Key_LeftShift` (or any modifier). Looking at the code, it seems like holding both of those keys down, plus a letter key – e.g. `lshift`+`lshift`+`A` – would result in a single erroneous HID report if one of those `lshift` keys (whichever one gets handled last) was released, because it would call `hid::releaseKey()`, clearing the bit for `lshift` in the report, and possibly resulting in this output, despite the fact that a `shift` key was being held the whole time: ```nohighlight AAAAAAaAAAAAAAA ``` [Note the `a`] I tried it out, and noticed that this doesn’t happen. I’m still not sure why, but I thought it might be because of repeat-rate limiting done by the OS. So I tried to slow down the keyboard by adding a single line at the end of `Kaleidoscope.loop()`: ```auto delay(1000); ``` I figured, with a guaranteed one-second gap between reports, the OS would certainly show what was happening. It didn’t. Instead, I saw very surprising things happen when I tapped multiple keys simultaneously. For example, when I very quickly rolled over `j`, `k`, and `l`, I saw this: ```nohighlight jjjjjjjjjkkkkkkkkklllllllllllllllllllllllllllllllllllllll ``` I was expecting the first key to be detected would be in one report alone, so the repeated `j` characters were not surprising, but on the next report after that, I thought I’d get the `k` and the `l` simultaneously, so whichever was detected first by the OS (`k`, most likely, because its bit appears first in the key report) would appear only once, then get masked. Here’s what I expected: ```nohighlight jjjjjjjjjklllllllll ``` …or maybe just: ```nohighlight jjjjjjjjj ``` …because, by the next loop, the scanner will have had time to do a couple hundred scan cycles. (I’m also trying to figure out how the scanners work). If it worked that way, though, I guess I probably wouldn’t see any output unless I got lucky or held the keys down long enough. Anyway, I’m just flummoxed. I added some serial debugging code to `Keyboard.sendReportUnchecked()`, and it shows this happening (the bitfield is the byte from `keyReport` including `j`, `k`, and `l`; the decimal number is `millis()`): ```nohighlight 40313: 00100000 41317: 01100000 42321: 11100000 43325: 11000000 44328: 10000000 45333: 00000000 ``` [Padded with zeroes for readability] The first line shows a report with `j` alone. Then, one second later, there’s a report with both `j` & `k`, but not `l`. This is ~one full second _after_ all three keys were released! Then, one more second passes, and `k` is added to the report. Then, almost three seconds and two full reports after the key was released, the `j` is finally removed from the key report. Then `k`, then, finally – _five seconds_ after it was released – a report is sent with `l` removed. Now, I’m not complaining about any actual behaviour here; it’s utterly ridiculous to have a one-second delay added to the main loop, of course. But I’m trying to understand how this all works, and I’m stumped by this one. What’s going on here? ---
**Author:** ![merlin](https://yyz1.discourse-cdn.com/flex031/user_avatar/community.keyboard.io/merlin/32/3416_2.png) [@merlin](https://community.keyboard.io/u/merlin)\ **Post date:** [January 24, 2018, 7:37pm UTC](https://community.keyboard.io/t/interesting-scanner-behaviour-that-i-cant-explain/950/2 "2018-01-24T19:37:37Z")
I’ve done a little more testing now. I added another debug line, to print when a key toggles on, and show its keycode in hex (in `handleKeyswitchEvent()`, after `Layer.lookup()`). Sometimes, when I try to tap all three keys simultaneously, I do see two of them change in the same report. Here’s the debug output: ```nohighlight key on: D 39359: 100000 key on: F key on: E 40374: 11100000 41377: 100000 42382: 0 ``` In this `D` = `j` (`0x0D`), `E` = `k` (`0x0E`), and `F` = `l` (`0x0F`). I only had it record keys toggling on. And in this case, the output is a bit more what I expected: ```nohighlight jjjjjjjjjklllllllll ``` …but this happens less often than the other pattern. So, I guess the keyscanner buffers several sets of key data, and I only get one of those each time `getKeyData()` is called? ---
**Author:** ![merlin](https://yyz1.discourse-cdn.com/flex031/user_avatar/community.keyboard.io/merlin/32/3416_2.png) [@merlin](https://community.keyboard.io/u/merlin)\ **Post date:** [January 24, 2018, 7:40pm UTC](https://community.keyboard.io/t/interesting-scanner-behaviour-that-i-cant-explain/950/3 "2018-01-24T19:40:53Z")
Now, I’ve even seen it once with all three keys toggling on in the same scan: ```nohighlight key on: F key on: E key on: D 701641: 11100000 702645: 100000 703649: 0 ``` …with this output (as expected): ```nohighlight jklllllllll ```