RX - minor optimizations/minor cleanup

[ledvinap]

• reuse millis() in rxInit
• rcData[] is float
• cleanup some float math
• fix GET_FRAME_ERR_LPF_FREQUENCY macro argument

[github-actions]

Do you want to test this code? You can flash it directly from Betaflight Configurator:

• Simply put #13493 (this pull request number) in the Select commit field of the Configurator firmware flasher tab (you need to Enable expert mode, Show release candidates and Development).

WARNING: It may be unstable. Use only for testing!

[ctzsnooze]

I guess the intent is that the LPF cutoff is set to ten times the inverse of the period ie 10Hz when period is 1s.
Perhaps it might be easier to conceptualise that relationship with:

define GET_FRAME_ERR_LPF_FREQUENCY(period) (10.0f / period)    // period is in seconds

[ledvinap]

betaflight/src/main/pg/rx.h

Line 59 in 5457032

uint8_t rssi_src_frame_lpf_period; // Period of the cutoff frequency for the source frame RSSI filter (in 0.1 s)

it is in 0.1s units

[ledvinap]

Can we get this merged? Except for not calling millis() multiple times, this PR makes not functional changes.

[nerdCopter]

for my understanding, is the uint32_t now = millis(); a one-time occurrence at init only, or continuous?

[ledvinap]

for my understanding, is the uint32_t now = millis(); a one-time occurrence at init only, or continuous?

It is used to initialize RC channel timeouts. Old code called millis() for each channel, now single timestamp is used in loop. The loop runs once, on RC initialization (rxInit).