Invalid coefficient of trim value

[chofchop]

Is there an existing issue for this problem?

• I have searched the existing issues

What part of EdgeTX is the focus of this bug?

Transmitter firmware

Current Behavior

In the current EdgeTX, the trim value takes values ​​from -1049 to 1049.

Expected Behavior

The trim value should be -1024~1024.
It has been multiplied by an extra 1.024 somewhere.

1024 x 1.024 = 1048.576 ≒ 1049

Steps To Reproduce

Display the trim value using Lua below.

local valuesToTest = {
  'ste',
  'thr',
  'trim-ste',
  'trim-thr',
  'trim-t3',
  'trim-t4',
  'trim-t5'
}
local run = function(evt, ts)
  lcd.clear()
  for i, valueName in ipairs(valuesToTest) do
    local value = getValue(valueName)
    lcd.drawText(10, (i - 1) * 8, valueName..' : '..tostring(value))
  end
  return (evt == EVT_EXIT_BREAK) and 1 or 0
end
return { run=run }

Version

2.10.5

Transmitter

RadioMaster MT12

Operating System (OS)

No response

OS Version

No response

Anything else?

No response

[philmoz]

It has been like this for a long time - at least 2.8 probably a lot longer.

While it could be changed, there is a risk of affecting existing scripts.

[chofchop]

Yes, I know that too, but that excuse is not reasonable.
If this obvious mistake is ignored, the number of affected scripts will continue to increase. I can't understand why they didn't fix it as soon as they noticed it.

[pfeerick]

1. This may be the first time it has been noticed, since it is still present, no?

2. This looks like it is only a minor scaling issue, so the risk of affecting existing setups is minimal and at worst requires a minor adjustment. Better to ascertain the cause and resolve it sooner than later.

[philmoz]

The cause is this line in mixer.cpp:

    return calc1000toRESX((int16_t)8 * trim_value);

trim_value range is -128 to 128 (or -512 to 512 with extended trims).
8 * trim_value range is -1024 to 1024.

calc1000toRESX assumes the input value range is -1000 to 1000 and scales it up to -1024 to 1024.

[chofchop]

I am testing by rewriting line 421 of mixer.cpp as shown below.

return (int16_t)8 * trim_value;

Although I have only been able to confirm part of it, it seems to be working properly on both the OS and the script so far.