Created modbus_transport_uart for bridging the nanomodbus library with HAL

Core/Src/modbus_transport_uart.c

@@ -0,0 +1,31 @@
+#include "nanomodbus.h"
+#include "main.h"
+#include "usart.h"  // for &huart2
+
+static uint8_t rx_buf[256];
+static uint8_t tx_buf[256];
+
+// nanoMODBUS requires this structure:
+mb_port_t modbus_port;
+
+// Read function (blocking or interrupt/DMA based)
+int modbus_read(uint8_t *dest, uint16_t len, uint32_t timeout_ms) {
+    if (HAL_UART_Receive(&huart2, dest, len, timeout_ms) == HAL_OK) {
+        return len;
+    }
+    return -1;
+}
+
+// Write function
+int modbus_write(const uint8_t *src, uint16_t len, uint32_t timeout_ms) {
+    if (HAL_UART_Transmit(&huart2, (uint8_t*)src, len, timeout_ms) == HAL_OK) {
+        return len;
+    }
+    return -1;
+}
+
+// Register your transport functions
+void modbus_transport_init(void) {
+    modbus_port.read = modbus_read;
+    modbus_port.write = modbus_write;
+}

lib/nanomodbus

@@ -1 +1 @@
-Subproject commit 469b5e88319a303e1231890af06f2634b825eb27
+Subproject commit 8780d6b81f4943ae83fa5b0102402c6bd71e01a5