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Support for 1.25MHz capture (#1418)

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* Advanced draft decim /4 just waterfall ok

* apply some Kall's corrections + formatting

* Tidy up both decim_factors

* New refine optimizations

* Format issues

* more format issues ...mmmm

* comments update

* WIP Cleanup

* WIP

* WIP - add variant

* Use std::visit to dispatch MultiDecimator -- fluent API

* Clean up comments

* Merge next and fix compilation

* Fix odd loop in BlockDecimator

* Clean up spectrum math

* Descibe spectrum update math better, more clear math.

* Apply spectrum interval correction at 1.5M

* Increase replay buffer to handle x4 ovs

---------

Co-authored-by: Brumi-2021 <ea3hqj@gmail.com>
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Kyle Reed 2023-08-29 10:26:38 -07:00 • committed by GitHub
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25
firmware/common/oversample.hpp
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@ -42,26 +42,27 @@
* In testing, a minimum rate of 400kHz seems to the functional minimum.
*
* There are several different concepts or terms related to Capture and Replay,
* (1) oversampling (x8, x16 ,...) / decimation (/8, /16...)
* In Capture App , when ADC can not handle directly a requiered low sample rates ,
* we need to apply oversampling (x8. x16 ex) , getting more real samples than needed) by "x_number" ,
* and later to write it to SD card with the proper needed real sample rate , we apply Decimation , "/ number" .
* (1) Oversampling (x8, x16, ...) and Decimation (/8, /16...)
* In Capture App, the ADC can not directly handle low sample rates.
* We need to apply oversampling (x8, x16, ...), collecting more "x number" additional real samples.
* To write it to SD card with the desired sample rate, we apply Decimation ("/ number").
*
* (2) up-sampling or re-escale or interpolation. (x8, x16, ...)
* In Replay-list App, when we got too low bit rate data for Hackrf ,
* we need to upsampling or interpolate or resampling to increase those low bit rates
* to a proper sample rate higher than the min. to be able to be transmitted by Hackrf.
* (2) Up-sampling or re-scale or interpolation. (x8, x16, ...).
* In Replay-list App, when the bit rate data is too low for HackRF.
* We need to upsample or interpolate to increase those low bit rates
* to a rate higher than the hardware nminimum to be transmitted by Hackrf.
*/
/* Gets the oversample rate for a given sample rate.
* The oversample rate is used to increase the sample rate to improve SNR and quality.
* This is also used as the interpolation rate when replaying captures. */
inline OversampleRate get_oversample_rate(uint32_t sample_rate) {
if (sample_rate < 30'000) return OversampleRate::x64; // 25k, 16k, 12k5.
if (sample_rate < 80'000) return OversampleRate::x32; // 75k, 50k, 32k.
if (sample_rate < 250'000) return OversampleRate::x16; // 100k and 150k.
if (sample_rate < 30'000) return OversampleRate::x64; // 25k, 16k, 12k5.
if (sample_rate < 80'000) return OversampleRate::x32; // 75k, 50k, 32k.
if (sample_rate < 250'000) return OversampleRate::x16; // 100k, 150k.
if (sample_rate < 1'250'000) return OversampleRate::x8; // 250k, 500k, 600k, 650k, 750k, 1Mhz.
return OversampleRate::x8; // 250k .. 1Mhz, that decim x8 , is already applied.(OVerSampling and decim OK)
return OversampleRate::x4; // Top range (1.25Mhz ... 5.5Mhz).
}
/* Gets the actual sample rate for a given sample rate.