nRF RPC UART transport

The nRF RPC UART transport allows you to use the Remote procedure call library (nRF RPC) library to execute procedures on a remote processor that is connected with the local processor using the UART interface. This transport is used in the Protocol serialization samples samples.

Frame encoding

Note

The current frame format is experimental and is a subject to change.

An nRF RPC packet that is sent using the nRF RPC UART transport is encoded within a frame whose format resembles the one used by the HDLC protocol.

Each frame shall start and end with the delimiter octet (0b01111110 = 0x7e). Each two subsequent frames may be separated by more than one delimiter octet.

Each byte of the nRF RPC packet shall be encoded according to the following rules:

  • If the byte matches one of the special octets, it shall be encoded as the following two octets:

    • the escape octet (0x7d),

    • the input byte XORed with 0x20.

  • Otherwise, the byte shall be encoded into a frame’s octet without changes.

The last two bytes of the frame contain the nRF RPC packet checksum, in little-endian byte order. The checksum is calculated using the CRC16_CCITT function with the initial value 0xffff.

Special octets

The following octets transmitted over the UART interface have a special meaning:

Value

Meaning

0x7d

escape

0x7e

delimiter

Encoding example

If the following nRF RPC packet is sent using the nRF RPC UART transport:

80 01 ff 00 00 61 7e f6

Then the following octets are transmitted over the UART interface:

7e 80 01 ff 00 00 61 7d 5e f6 6d 72 7e

API documentation

Header file: include/nrf_rpc/nrf_rpc_uart.h
Source file: subsys/nrf_rpc/nrf_rpc_uart.c
group nrf_rpc_uart

nRF RPC UART transport.

Defines

NRF_RPC_UART_TRANSPORT(node_id)

Returns nRF RPC UART transport object name for the given devicetree node.

Parameters:

  • node_id – Devicetree node of the selected UART peripheral (e.g. DT_NODELABEL(uart0)).