wayne roberts / SX127x

Driver library for SX1272/SX1276 transceivers

Dependents:   LORA_RX LORA_TX WindConcentrator hid_test ... more

Driver library for SX1272 and SX1276 radio transceivers.

This device uses CSS modulation to provide much improved link budget. The RF hardware is same as in FSK devices, just with added LoRa spread-spectrum modem.

This library provides functions to configure radio chip and transmit & receive packets.

Using This Library

Library function service_radio() must be called continuously from main loop, to service interrupts from radio.

Board Specific implementation

FunctionPointer for rf_switch callback allows the program to implement control of RF switch unique to their board. Example options are:

• SKY13373 for external power amplifier implementation. Requires two DigitalOut pins.
• SKY13350 using PA_BOOST. requires two DigitalOut pins.
• PE4259-63: controlled directly by radio chip, no software function needed. However, in the case of SX1276MB1xAS, the RXTX pin on IO2 should be driven by this callback function when R16 is installed (without R15) on this shield board.

Some configurations may need to force the use of RFO or PA_BOOST, or a board could offer both options. The rf_switch function pointer callback should support the implementation choice on the board.

further reading

• LoRa modulation basics (dropbox PDF)
• OpenLoRa forum

--- a/sx127x_lora.h	Thu Feb 26 23:31:36 2015 +0000
+++ b/sx127x_lora.h	Fri Feb 27 22:50:18 2015 +0000
@@ -113,7 +113,7 @@
     struct {    // sx127x register 0x26
         uint8_t reserved    : 2;    // 0,1
         uint8_t AgcAutoOn   : 1;    // 2
-        uint8_t LowDataRateOptimize  : 1;    // 3   ppm_offset
+        uint8_t LowDataRateOptimize  : 1;    // 3   ppm_offset, use when symbol duration exceeds 16ms
         uint8_t unused      : 4;    // 4,5,6,7 
     } sx1276bits;
     uint8_t octet;
@@ -191,6 +191,11 @@
         
         float get_pkt_rssi(void);
         
+        /** retrieve symbol duration from bandwidth and spreading factor
+         * @returns symbol duration in milliseconds
+         */        
+        float get_symbol_period(void);
+        
         service_action_e service(void); // (SLIH) ISR bottom half 
         
         bool poll_vh;