JP_STRICT: adjust MAX_TEXT_LEN based on LORA_CR setting

MAX_TEXT_LEN is automatically selected based on the LORA_CR build flag
defined in platformio.ini (e.g. -D LORA_CR=5).

CR4/5: 48 bytes (~16 JP chars, TX ~3808ms)
CR4/6: 32 bytes (~10 JP chars)
CR4/7: 24 bytes (~8 JP chars)
CR4/8: 16 bytes (~5 JP chars, default)

To enable CR4/5 for Japan, add -D LORA_CR=5 to your board's
build_flags in platformio.ini. Set LORA_CR=5 for WioTrackerL1 and RAK WisMesh Tag.

Author: jirogit

src/helpers/BaseChatMesh.h

@@ -6,12 +6,24 @@
 #include <helpers/TxtDataHelpers.h>
 
 // JP_STRICT: limit MAX_TEXT_LEN to keep TX time under 4s (ARIB STD-T108)
-// SF12/BW125/CR4-8: 60 bytes total packet = ~3809ms, overhead ~44 bytes
-// leaving 16 bytes (1*CIPHER_BLOCK_SIZE) for text payload
+// SF12/BW125, packet overhead ~44 bytes
+// CR4/5: 100 bytes total = ~3808ms → 56 bytes text → ~18 JP chars
+// CR4/6: 80 bytes total  = ~3530ms → 36 bytes text → ~12 JP chars
+// CR4/7: 70 bytes total  = ~3530ms → 26 bytes text →  ~8 JP chars
+// CR4/8: 60 bytes total  = ~3809ms → 16 bytes text →  ~5 JP chars
 #ifdef JP_STRICT
-  #define MAX_TEXT_LEN  (1*CIPHER_BLOCK_SIZE)   // ~16 chars, TX <= 4s for JP
+  #if defined(LORA_CR) && (LORA_CR == 5)
+    #define MAX_TEXT_LEN  (3*CIPHER_BLOCK_SIZE)    // 48 bytes ~18 JP chars
+  #elif defined(LORA_CR) && (LORA_CR == 6)
+    #define MAX_TEXT_LEN  (2*CIPHER_BLOCK_SIZE)    // 32 bytes ~10 JP chars
+  #elif defined(LORA_CR) && (LORA_CR == 7)
+    #define MAX_TEXT_LEN  (1*CIPHER_BLOCK_SIZE+8)  // 24 bytes ~8 JP chars
+  #else
+    #define MAX_TEXT_LEN  (1*CIPHER_BLOCK_SIZE)    // 16 bytes ~5 JP chars
+  #endif
 #else
-  #define MAX_TEXT_LEN  (10*CIPHER_BLOCK_SIZE)  // must be LESS than (MAX_PACKET_PAYLOAD - 4 - CIPHER_MAC_SIZE - 1)
+  #define MAX_TEXT_LEN  (10*CIPHER_BLOCK_SIZE)  
+// must be LESS than (MAX_PACKET_PAYLOAD - 4 - CIPHER_MAC_SIZE - 1)
 #endif
 
 #include "ContactInfo.h"

variants/rak_wismesh_tag/platformio.ini

@@ -26,6 +26,7 @@ build_flags = ${nrf52_base.build_flags}
   -D PIN_BOARD_SDA=PIN_WIRE_SDA
   -D PIN_BOARD_SCL=PIN_WIRE_SCL
   -D JP_STRICT
+  -D LORA_CR=5
 build_src_filter = ${nrf52_base.build_src_filter}
   +<../variants/rak_wismesh_tag>
   +<helpers/ui/MomentaryButton.cpp>

variants/wio-tracker-l1/platformio.ini

@@ -17,6 +17,7 @@ build_flags = ${nrf52_base.build_flags}
   -D PIN_OLED_RESET=-1
   -D GPS_BAUD_RATE=9600
   -D JP_STRICT
+  -D LORA_CR=5
 build_src_filter = ${nrf52_base.build_src_filter}
   +<WioTrackerL1Board.cpp>
   +<../variants/wio-tracker-l1>