Add embedded storage drivers and extend firmware metadata

c/modbus/include/modbus_data.h

@@ -0,0 +1,15 @@
+#ifndef SET_MODBUS_DATA_H
+#define SET_MODBUS_DATA_H
+#include <stddef.h>
+#include <stdint.h>
+/* Decoded Modbus values, independent of UART/HAL and register addresses.
+ * Coils in bank use bit 0 first in 16-bit words. Message words contain two
+ * wire bytes, first byte in bits 15..8 (same convention as register messages).
+ * The port validates/maps the complete address range before calling transfer.
+ * Return standard Modbus exceptions: 0 success, 1 function, 3 value. */
+uint8_t mb_data_validate(uint8_t function, uint16_t quantity, uint16_t byte_count,
+                         size_t data_capacity);
+uint8_t mb_data_transfer(uint8_t function, uint16_t quantity, uint16_t byte_count,
+                         uint16_t *bank, uint16_t bit_offset, uint16_t *data,
+                         size_t data_capacity, uint16_t *response_bytes);
+#endif