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soypat
131 lines
3.0 KiB
Go
131 lines
3.0 KiB
Go
package lora
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import "time"
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type Config struct {
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// Bandwidth relates to data rate of communication. Double the bandwidth means
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// double the data rate, which implies faster communications and less energy usage.
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Bandwidth Frequency
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Frequency Frequency
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// Length of the preamble preceding the header. Can be arbitrarily long.
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// Longer preambles ensure more robust communications but can lead to congestion.
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//
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// Note: The preamble length on a receiver should be configured equal-to or greater
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// than the expected packet preamble length on the SX1278.
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PreambleLength uint16
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HeaderType HeaderType
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CodingRate CodingRate
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SpreadFactor SpreadFactor
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SyncWord uint8
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TxPower int8 // Tx Power in dBm.
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CRC bool
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// Low data rate optimisation flag. The use of this flag is mandated when
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// the symbol duration exceeds 16ms. Increases reliability at high spreading factors.
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LDRO bool
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IQMode uint8
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}
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func (cfg *Config) TimeOnAir(payloadLength int) time.Duration {
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if cfg.Bandwidth == 0 {
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return 0
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}
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crc := int64(b2u8(cfg.CRC))
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ih := int64(cfg.HeaderType)
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ldr := int64(b2u8(cfg.LDRO))
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cr := int64(cfg.CodingRate)
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spread := int64(cfg.SpreadFactor)
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// Page 31 SX1276IMLTRT SEMTECH | Alldatasheet.
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Npayload := 8*int64(payloadLength) - 4*spread + 28 + 16*crc - 20*ih
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div := 4 * (spread - 2*ldr)
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// Apply Ceil and max with minimal branching.
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if Npayload < 0 || div <= 0 {
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Npayload = 0
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} else if Npayload%div == 0 {
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Npayload /= div
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Npayload *= (cr + 4)
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} else {
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Npayload /= div
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Npayload++
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Npayload *= (cr + 4)
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}
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Npayload += 8 + int64(cfg.PreambleLength) + 5 // Says 4.25 in manual but we round up.
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// Calculate LoRa Transmission Parameter Relationship page 28.
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Ts_us := 1000_000 * cfg.SpreadFactor.ChipsPerSymbol() / cfg.Bandwidth.Hertz()
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return time.Microsecond * (time.Duration(Npayload * Ts_us))
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}
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type HeaderType uint8
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const (
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HeaderExplicit HeaderType = 0
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HeaderImplicit HeaderType = 1
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)
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type CodingRate uint8
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const (
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CR4_5 CodingRate = 1
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CR4_6 CodingRate = 2
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CR4_7 CodingRate = 3
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CR4_8 CodingRate = 4
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)
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type SpreadFactor uint8
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const (
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SF6 SpreadFactor = iota + 6
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SF7
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SF8
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SF9
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SF10
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SF11
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SF12
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)
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func (sf SpreadFactor) ChipsPerSymbol() int64 {
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return 1 << sf
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}
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type Frequency int64
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func (f Frequency) Hertz() int64 { return int64(f) }
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const (
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Hertz Frequency = 1
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KiloHertz Frequency = 1000 * Hertz
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MegaHertz Frequency = 1000 * KiloHertz
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)
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// Common LoRa bandwidths
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const (
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BW125k = 125 * KiloHertz
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BW250k = 250 * KiloHertz
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BW500k = 500 * KiloHertz
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)
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// Common LoRa frequencies
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const (
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// 433.05MHz Low limit medical, scientific and industrial band.
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Freq433_0M = 433050000 * Hertz
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// 434.8MHz High limit medical, scientific and industrial band.
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Freq434_8M = 434790000 * Hertz
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Freq868_1M = 868100000 * Hertz
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Freq868_5M = 868500000 * Hertz
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Freq916_8M = 916800000 * Hertz
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Freq923_3M = 923300000 * Hertz
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)
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func max[T ~int | ~int64 | ~uint8](a, b T) T {
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if a > b {
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return a
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}
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return b
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}
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func b2u8(b bool) uint8 {
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if b {
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return 1
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}
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return 0
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}
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