fix: remove SDA/SCL/TX/RX intermediate macros from nRF52 board headers

The nRF52840 board headers were defining SDA, SCL, TX and RX as numeric
preprocessor macros (with #ifndef guards) and then assigning them to the
BOARD_I2C_SDA / BOARD_UART_RX aliases.  This caused a cascade of parse
errors because board_config.h is included before Arduino.h, and the nRF52
SDK header nrf52.h declares struct members named SDA, SCL and RX — the
preprocessor replaces those identifiers with their numeric values, turning
valid struct declarations into syntax errors.

Fix: assign pin numbers directly to the BOARD_* macros so that SDA, SCL,
TX and RX are never defined as macros.  The nRF52 platform variant still
exposes them as const uint8_t variables after Arduino.h is processed, which
is fine because our code only references the BOARD_* names.

Both nRF52840-DK and nRF52840 Feather headers are updated.

https://claude.ai/code/session_01KcwgryFgMCJubfjtwqMnUc

Author: claude

include/boards/board_nrf52840_dk.h

@@ -24,31 +24,21 @@
 // ── I2C ──────────────────────────────────────────────────────────────────────
 // Arduino Wire on nRF52 uses the pins defined by the board variant.
 // nRF52840-DK default: P0.26 = SDA, P0.27 = SCL.
-// The macros SDA / SCL are provided by the nordicnrf52 platform variant; the
-// fallback values below match the DK schematic in case they are not defined.
-#ifndef SDA
-#  define SDA 26
-#endif
-#ifndef SCL
-#  define SCL 27
-#endif
-#define BOARD_I2C_SDA       SDA
-#define BOARD_I2C_SCL       SCL
+// Do NOT define SDA/SCL as macros here — nrf52.h has struct members with
+// those names and the preprocessor would clobber them.
+#define BOARD_I2C_SDA       26
+#define BOARD_I2C_SCL       27
 #define BOARD_I2C_FREQ      400000UL
 
 // ── UART ─────────────────────────────────────────────────────────────────────
 // Serial is USB CDC (no physical pins needed).
-// Serial1 is on the Arduino header; TX and RX macros come from the variant.
-#ifndef TX
-#  define TX 6   // P0.06
-#endif
-#ifndef RX
-#  define RX 8   // P0.08
-#endif
-#define BOARD_UART_TX       TX
-#define BOARD_UART_RX       RX
-#define BOARD_UART1_TX      TX
-#define BOARD_UART1_RX      RX
+// Serial1 is on the Arduino header; P0.06 = TX, P0.08 = RX.
+// TX and RX are also struct-member names in the nRF52 SDK; define only the
+// BOARD_ aliases to avoid clashes.
+#define BOARD_UART_TX       6    // P0.06
+#define BOARD_UART_RX       8    // P0.08
+#define BOARD_UART1_TX      6
+#define BOARD_UART1_RX      8
 
 // ── Status LED ───────────────────────────────────────────────────────────────
 // LED1–LED4 are active LOW on the nRF52840-DK.

include/boards/board_nrf52840_feather.h

@@ -16,30 +16,21 @@
 
 // ── I2C ──────────────────────────────────────────────────────────────────────
 // SDA and SCL are labelled on the Feather silkscreen.
-// Adafruit nRF52 Arduino core maps: SDA = P0.12, SCL = P0.11.
-// The SDA/SCL macros are defined by the Adafruit nRF52 platform variant.
-#ifndef SDA
-#  define SDA 25   // Adafruit nRF52 Arduino pin 25 → P0.12
-#endif
-#ifndef SCL
-#  define SCL 26   // Adafruit nRF52 Arduino pin 26 → P0.11
-#endif
-#define BOARD_I2C_SDA       SDA
-#define BOARD_I2C_SCL       SCL
+// Adafruit nRF52 Arduino core maps: SDA = P0.12 (pin 25), SCL = P0.11 (pin 26).
+// Do NOT define SDA/SCL as macros — nrf52.h has struct members with those
+// names and the preprocessor would clobber them.
+#define BOARD_I2C_SDA       25   // Adafruit nRF52 Arduino pin 25 → P0.12
+#define BOARD_I2C_SCL       26   // Adafruit nRF52 Arduino pin 26 → P0.11
 #define BOARD_I2C_FREQ      400000UL
 
 // ── UART ─────────────────────────────────────────────────────────────────────
-// Serial is USB CDC.  Serial1 maps to the Feather TX/RX pads.
-#ifndef TX
-#  define TX 25   // P0.25
-#endif
-#ifndef RX
-#  define RX 24   // P0.24
-#endif
-#define BOARD_UART_TX       TX
-#define BOARD_UART_RX       RX
-#define BOARD_UART1_TX      TX
-#define BOARD_UART1_RX      RX
+// Serial is USB CDC.  Serial1 maps to the Feather TX/RX pads (P0.25/P0.24).
+// TX and RX are also struct-member names in the nRF52 SDK; define only the
+// BOARD_ aliases.
+#define BOARD_UART_TX       25   // P0.25
+#define BOARD_UART_RX       24   // P0.24
+#define BOARD_UART1_TX      25
+#define BOARD_UART1_RX      24
 
 // ── Status LEDs ──────────────────────────────────────────────────────────────
 // Red LED and Blue LED both active LOW.