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Add tap_random_base64 and software timer info to Useful Functions doc #4360

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Dec 1, 2018
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Add tap_random_base64 and software timer info to Useful Functions doc #4360

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Update docs
drashna Nov 5, 2018
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Add security caveat
vomindoraan Nov 5, 2018
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Wordsmithing
vomindoraan Nov 5, 2018
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Update docs/ref_functions.md
vomindoraan Nov 5, 2018
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17 changes: 0 additions & 17 deletions docs/faq_keymap.md
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Original file line number Diff line number Diff line change
Expand Up @@ -211,20 +211,3 @@ here real_mods lost state for 'physical left shift'.

weak_mods is ORed with real_mods when keyboard report is sent.
https://github.com/tmk/tmk_core/blob/master/common/action_util.c#L57

## Timer Functionality

It's possible to start timers and read values for time-specific events - here's an example:

```c
static uint16_t key_timer;
key_timer = timer_read();

if (timer_elapsed(key_timer) < 100) {
// do something if less than 100ms have passed
} else {
// do something if 100ms or more have passed
}
```

It's best to declare the `static uint16_t key_timer;` at the top of the file, outside of any code blocks you're using it in.
21 changes: 21 additions & 0 deletions docs/ref_functions.md
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Expand Up @@ -96,3 +96,24 @@ And to do so, add `reset_keyboard()` to your function or macro, and this will re
If you're having issues with Audio, RGB Underglow, backlighting or keys acting weird, then you can reset the EEPROM (persistent setting storage). Bootmagic is one way to do this, but if that isn't enabled, then you can use a custom macro to do so.

To wipe the EEPROM, run `eeconfig_init()` from your function or macro to reset most of the settings to default.

## Tap random key

If you want to send a random character to the host computer, you can use the `tap_random_base64()` function. This [pseudorandomly](https://en.wikipedia.org/wiki/Pseudorandom_number_generator) selects a number between 0 and 63, and then sends a key press based on that selection. (0–25 is `A`–`Z`, 26–51 is `a`–`z`, 52–61 is `0`–`9`, 62 is `+` and 63 is `/`).

?> Needless to say, but this is _not_ a cryptographically secure method of generating random Base64 keys or passwords.
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Suggested change
?> Needless to say, but this is _not_ a cryptographically secure method of generating random Base64 keys or passwords.
?> Needless to say, this is _not_ a cryptographically secure method of generating random Base64 keys or passwords.

Woops, didn't proofread.


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## Software Timers

It's possible to start timers and read values for time-specific events. Here's an example:

```c
static uint16_t key_timer;
key_timer = timer_read();
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This is probably a bug: the timer will be reinitialized every time the function is called, effectively making the static declaration pointless (i.e. only the else branch will ever be executed). You should probably do static uint16_t key_timer = timer_read(); here instead, but I think that's a bit misleading too. Namely, this will make the timed event only ever trigger once, as timer_read() will only be called the first time the function is run.

A better alternative would be to set the timer in an if statement, then read and compare the elapsed time in the else branch, as is often done in keymaps:

static uint16_t key_timer;

if (record->event.pressed) {
  key_timer = timer_read();
} else {
  if (timer_elapsed(key_timer) < 100) {
    // Do something if less than 100 ms has passed
  } else {
    // Do something if 100 ms or more has passed
  }
}


if (timer_elapsed(key_timer) < 100) {
// do something if less than 100ms have passed
} else {
// do something if 100ms or more have passed
}
```