feat: Draft architecture for incp hub

app/src/ntl/CMakeLists.txt

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+target_include_directories(${EXECUTABLE} PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/include)

app/src/ntl/README.md

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+# NTL
+
+Nanosatlab Transport Layer (from IP model)
+
+## Byte ordering
+
+Multi-byte fields are sent in little-endian order. (Natural order for x86 and arm)

app/src/ntl/include/ntl/ntl.h

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+#ifndef NTL_H_
+#define NTL_H_
+
+#include <stdint.h>
+
+
+
+// === Type Aliases ===
+
+/// @brief An NTL port number
+typedef uint8_t ntl_port_t;
+/// @brief An NTL check value
+typedef uint32_t ntl_chk_t;
+
+
+
+// === Special Port Values ===
+
+/// @brief Denotes an invalid port number
+#define NTL_PORT_EMPTY ((ntl_port_t)0)
+/// @brief The highest valid port number
+#define NTL_MAX_PORT (~(ntl_port_t)0)
+
+
+
+// === Special Check Values ===
+
+/// @brief Denotes no check value to validate
+#define NTL_CHK_EMPTY ((ntl_chk_t)0)
+
+
+
+// === Struct Definitions ===
+
+/// @brief Packed header format
+typedef struct __attribute__((packed, aligned(4))) {
+	ntl_port_t dst_port;
+	ntl_port_t src_port;
+	uint16_t len;
+	ntl_chk_t chk;
+} ntl_header_t;
+
+/// @brief An NTL packet (packed) with header and payload
+typedef struct __attribute__((packed, aligned(4))) {
+    ntl_header_t header;
+    uint8_t payload[];
+} ntl_packet_t;
+
+
+
+// === Convenience Functions ===
+
+/// @brief Convert uint16 value from host to network byte order
+/// @param value The value in host order
+/// @return The value in network order
+static inline uint16_t ntl_htons(uint16_t value)
+{
+#if defined(__BYTE_ORDER) && __BYTE_ORDER == __BIG_ENDIAN || \
+    defined(__BIG_ENDIAN__) || \
+    defined(__ARMEB__) || \
+    defined(__THUMBEB__) || \
+    defined(__AARCH64EB__) || \
+    defined(_MIBSEB) || defined(__MIBSEB) || defined(__MIBSEB__)
+	return ((value << 8) & 0xFF) | ((value & 0xFF) << 8);
+#elif defined(__BYTE_ORDER) && __BYTE_ORDER == __LITTLE_ENDIAN || \
+    defined(__LITTLE_ENDIAN__) || \
+    defined(__ARMEL__) || \
+    defined(__THUMBEL__) || \
+    defined(__AARCH64EL__) || \
+    defined(_MIPSEL) || defined(__MIPSEL) || defined(__MIPSEL__)
+	return value;
+#else
+	#error "Unable to detect byte endianness of platform."
+#endif
+}
+
+/// @brief Populates an NTL header from the provided fields
+/// @param hdr The header to pupulate
+/// @param dst The destination port
+/// @param src The source port
+/// @param len The length of the NTL payload in bytes
+static inline void ntl_build_header(volatile ntl_header_t *hdr, ntl_port_t dst, ntl_port_t src, uint16_t len)
+{
+    hdr->dst_port = dst;
+    hdr->src_port = src;
+    hdr->len = ntl_htons(len);
+    //REVIEW: Disabled for now, add a flag to set this to an actual check?
+    hdr->chk = NTL_CHK_EMPTY;
+}
+
+static inline ntl_port_t ntl_get_dst(const ntl_header_t *hdr) { return hdr->dst_port; }
+static inline ntl_port_t ntl_get_src(const ntl_header_t *hdr) { return hdr->src_port; }
+static inline ntl_port_t ntl_get_len(const ntl_header_t *hdr) { return ntl_htons(hdr->len); }
+static inline ntl_port_t ntl_get_chk(const ntl_header_t *hdr) { return hdr->chk; }
+
+#endif