From 44b7930a0167622763381f6dd39ce34308580941 Mon Sep 17 00:00:00 2001
From: Justin Stephens <justephens@protonmail.com>
Date: Fri, 12 Nov 2021 18:28:09 -0500
Subject: [PATCH] Added support for on-the-fly FIFO refilling in FSK. FSK can
 now transmit variable-length packets up to 255 long, as specified in the data
 sheet.

---
 src/modules/SX127x/SX127x.cpp | 38 +++++++++++++++++++++++++++--------
 src/modules/SX127x/SX127x.h   |  4 ++--
 2 files changed, 32 insertions(+), 10 deletions(-)

diff --git a/src/modules/SX127x/SX127x.cpp b/src/modules/SX127x/SX127x.cpp
index b0f1f8ab..5f518a1e 100644
--- a/src/modules/SX127x/SX127x.cpp
+++ b/src/modules/SX127x/SX127x.cpp
@@ -472,6 +472,15 @@ int16_t SX127x::startTransmit(uint8_t* data, size_t len, uint8_t addr) {
     state |= _mod->SPIsetRegValue(SX127X_REG_FIFO_TX_BASE_ADDR, SX127X_FIFO_TX_BASE_ADDR_MAX);
     state |= _mod->SPIsetRegValue(SX127X_REG_FIFO_ADDR_PTR, SX127X_FIFO_TX_BASE_ADDR_MAX);
 
+    // write packet to FIFO
+    _mod->SPIwriteRegisterBurst(SX127X_REG_FIFO, data, len);
+
+    // set RF switch (if present)
+    _mod->setRfSwitchState(LOW, HIGH);
+
+    // start transmission
+    state |= setMode(SX127X_TX);
+
   } else if(modem == SX127X_FSK_OOK) {
     // check packet length
     if(len >= SX127X_MAX_PACKET_LENGTH_FSK) {
@@ -494,16 +503,29 @@ int16_t SX127x::startTransmit(uint8_t* data, size_t len, uint8_t addr) {
     if((filter == SX127X_ADDRESS_FILTERING_NODE) || (filter == SX127X_ADDRESS_FILTERING_NODE_BROADCAST)) {
       _mod->SPIwriteRegister(SX127X_REG_FIFO, addr);
     }
+    
+    // Pre-load the FIFO with message before entering TX mode
+    uint8_t* ind = data;
+    _mod->SPIwriteRegisterBurst(SX127X_REG_FIFO, ind, min(len, 64));
+    ind += min(len, 64);
+
+    // set RF switch (if present) and start transmitting
+    _mod->setRfSwitchState(LOW, HIGH);
+    state |= setMode(SX127X_TX);
+
+    // Re-fill the FIFO on-the-fly as bytes are transmitted
+    while (ind < data + len) {
+      uint16_t flags = getIRQFlags();
+      bool fifo_full = flags >> 15;
+
+      // If FIFO not full, write another byte
+      if (!fifo_full) {
+        _mod->SPIwriteRegister(SX127X_REG_FIFO, *ind);
+        ind++;
+      }
+    }
   }
 
-  // write packet to FIFO
-  _mod->SPIwriteRegisterBurst(SX127X_REG_FIFO, data, len);
-
-  // set RF switch (if present)
-  _mod->setRfSwitchState(LOW, HIGH);
-
-  // start transmission
-  state |= setMode(SX127X_TX);
   RADIOLIB_ASSERT(state);
 
   return(ERR_NONE);
diff --git a/src/modules/SX127x/SX127x.h b/src/modules/SX127x/SX127x.h
index dc33ec08..b8347c2c 100644
--- a/src/modules/SX127x/SX127x.h
+++ b/src/modules/SX127x/SX127x.h
@@ -12,7 +12,7 @@
 // SX127x physical layer properties
 #define SX127X_FREQUENCY_STEP_SIZE                    61.03515625
 #define SX127X_MAX_PACKET_LENGTH                      255
-#define SX127X_MAX_PACKET_LENGTH_FSK                  64
+#define SX127X_MAX_PACKET_LENGTH_FSK                  255
 #define SX127X_CRYSTAL_FREQ                           32.0
 #define SX127X_DIV_EXPONENT                           19
 
@@ -601,7 +601,7 @@ class SX127x: public PhysicalLayer {
     int16_t beginFSK(uint8_t chipVersion, float br, float freqDev, float rxBw, uint16_t preambleLength, bool enableOOK);
 
     /*!
-      \brief Binary transmit method. Will transmit arbitrary binary data up to 255 bytes long using %LoRa or up to 63 bytes using FSK modem.
+      \brief Binary transmit method. Will transmit arbitrary binary data up to 255 bytes long.
       For overloads to transmit Arduino String or C-string, see PhysicalLayer::transmit.
 
       \param data Binary data that will be transmitted.