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POCSAG2 Revised bit extractor (#1439)

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* Better bit extraction WIP
* Parallel clock signal detection for bit extraction
* Relax clock detection accuracy.
* Reset RateInfo state. TODOs
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Kyle Reed 2023-09-09 06:18:42 -07:00 • committed by GitHub
parent b3312a704a
commit 4926cf8df5
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2 changed files with 77 additions and 152 deletions
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52
firmware/baseband/proc_pocsag2.hpp
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@ -84,52 +84,38 @@ class BitExtractor {
void extract_bits(const buffer_f32_t& audio);
void configure(uint32_t sample_rate);
void reset();
uint16_t baud_rate() const;
private:
/* Number of rate misses that would cause a rate update. */
static constexpr uint8_t rate_miss_reset_threshold = 5;
/* Clock signal detection magic number. */
static constexpr uint32_t clock_magic_number = 0xAAAAAAAA;
/* Number of rate misses that would cause a rate update. */
static constexpr uint8_t bad_transition_reset_threshold = 10;
struct RateInfo {
const int16_t baud_rate = 0;
float sample_interval = 0.0;
struct BaudInfo {
uint16_t baud_rate = 0;
float bit_length = 0.0;
float min_bit_length = 0.0;
float max_bit_length = 0.0;
float samples_until_next = 0.0;
float last_sample = 0.0;
BitQueue bits{};
};
/* Handle a transition, returns true if "good". */
bool handle_transition();
/* Updates a rate info with the given sample.
* Returns true if the rate info has a new bit in its queue. */
bool handle_sample(RateInfo& rate, float sample);
/* Count the number of bits the length represents.
* Returns true if valid given the current baud rate. */
bool count_bits(uint32_t length, uint16_t& bit_count);
/* Gets the best baud info associated with the specified bit length. */
const BaudInfo* get_baud_info(float bit_length) const;
std::array<BaudInfo, 3> known_rates_{
BaudInfo{512},
BaudInfo{1200},
BaudInfo{2400}};
std::array<RateInfo, 3> known_rates_{
RateInfo{512},
RateInfo{1200},
RateInfo{2400}};
BitQueue& bits_;
uint32_t sample_rate_ = 0;
uint16_t min_valid_length_ = 0;
const BaudInfo* current_rate_ = nullptr;
uint8_t rate_misses_ = 0;
RateInfo* current_rate_ = nullptr;
float sample_ = 0.0;
float last_sample_ = 0.0;
float next_bit_center_ = 0.0;
uint32_t sample_index_ = 0;
uint32_t last_transition_index_ = 0;
uint32_t bad_transitions_ = 0;
float samples_until_next_ = 0.0;
float prev_sample_ = 0.0;
bool ready_to_send_ = false;
};
/* Extracts codeword batches from the BitQueue. */