Send API

xgl_send() is the default send API.

Data Ownership

tx_data->data is borrowed for the duration of the call. Reliable sends require stable retransmission storage, so the protocol keeps a copy or equivalent storage.

Reliable and Unreliable

Mode	Behavior
unreliable	Send without waiting for ACK
reliable	Allocate packet number, enter reliable queue, wait for ACK range/SACK

Fragmentation

If payload exceeds route MTU and fragmentation is enabled, FRAGMENT_EXT is used. Otherwise send fails.

Callback

Application callbacks receive only payloads that passed CRC, authentication, routing, and reliability handling.

Send Failure Handling

Error	Common Cause	Handling
XGL_ERR_ROUTE_NOT_FOUND	No route to target	Check route table
XGL_ERR_BUFFER_TOO_SMALL	Frame exceeds route MTU or caller buffer is too small	Reduce payload, enable fragmentation, or increase MTU
XGL_ERR_WINDOW_FULL	Reliable window is full	Retry later or increase window/queue budget
XGL_ERR_NO_MEMORY	Allocator/pool budget exhausted	Tune resource model
XGL_ERR_TX_FAILED	PHY send failed	Inspect driver and link

Application data_type

data_type classifies application payload. It is not the reliability ordering primitive and is not written into wire packet_type. When non-zero, it is encoded as DATA_TYPE_EXT in the header TLV area. Protocol control semantics use packet type and TLV extensions.