Protocol Encoder

Encode input data into a uint8 byte stream by specifying the packet structure

Since R2021b

Add-On Required: This feature requires the Simulink Support Package for Raspberry Pi Hardware add-on.

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Libraries:
Simulink Support Package for Raspberry Pi Hardware / Utilities
Simulink Support Package for Arduino Hardware / Common
C2000 Microcontroller Blockset / Target Communication

Description

The Protocol Encoder encodes input data into a uint8 byte stream as per the specified packet structure based on the communication protocol. You can use this block to encode the separate fields into a packet, by specifying the header, terminator, name of packet fields in sequence and their size. You can also generate checksum bytes for the packet for validating the packet.

Ports

Input

Field1 — First field to be encoded by the block

scalar

First field to be encoded by the block. The name of input port is defined using the block parameter Field name. Each subsequent field that you create while defining the packet structure results in a new input port, with the Field name value appearing as the name of input port.

The block can have from 1 to N input ports. N is the number of fields in the packet structure that you specify in the Specify packet fields sequentially pane.

Output

Packet — uint8 byte stream packet

vector

The uint8 byte stream packet that contains the encoded data from multiple signals as specified in the packet structure.

Data Types: uint8

Parameters

Header — Header of the packet

character array | array of numeric values less than 255

Specify the header that indicates the beginning of the encoded data. The encoded output data will begin with the header.

The numeric array specified in this parameter is the uint8 integer representation of the corresponding ASCII characters.

Few examples of header values are: ‘START’, '$’, 36, [36,37].

Specify packet fields sequentially

Field name — Name of the field in the packet structure

Field1 (default) | string

Specify the name of the field to be included in the packet structure. This name appears as the name of the input port.

To add a new packet field and specify its properties, click Add. After adding a field, click Move Up or Move Down to change its sequence in the structure.

To delete a field and its properties, select the row and click Delete.

Input field length — Length of the input field as per the data type

1 (default) | numeric scalar

Length of the input field as per the data type that you enter in the next column (Input field data type). For example, if the Input field data type of a field is ‘uint16’ and the length is 1, the encoder converts the input into two uint8 bytes in the output packet.

Input field data type — Data type of the field

uint8 (default) | int8 | int16 | uint16 | int32 | uint32 | int64 | uint64 | single | double

Select the data type of the field.

Note

double is considered as 8 bytes. If your hardware does not support 8 bytes double, selecting this data type might give incorrect results.

Byte order — Endianess of the field in the packet

Little endian (default) | Big endian

Select the endianess of the packet field to describe the order in which bytes are unpacked.

Specify logic to generate checksum for validation — Enable the logic for checksum validation and select the logic

XOR of bytes | 2's complement of sum of bytes | Custom algorithm

Specify the logic to generate checksum for validation using standard algorithms or a custom algorithm.

If the logic is selected as XOR of bytes, the block calculates checksum as a single byte which is XOR of all bytes excluding header, terminator (if applicable).

If the logic is selected as 2's complement of sum of bytes, the block calculates checksum as a single byte which is the 2's complement of sum off all bytes excluding header and terminator (if applicable).

If you select Custom algorithm, the additional parameters – Checksum size and File path – are enabled. In this case, you can provide your own custom logic to validate packet. The checksum bytes returned by the custom logic should be of size specified in the Checksum size field and these bytes will be appended to the packet. For more information, see Function Template for Custom Checksum Logic in Protocol Encoder Block.

For the encoded packet in all the above three cases, checksum bytes are appended either at the end (if terminator is not available) or before the terminator (if terminator is specified).

Checksum size — Size of checksum bytes specified in the function used for custom algorithm

numeric scalar

Specify size of the checksum bytes generated by the function used for custom algorithm. For more details, see Function Template for Custom Checksum Logic in Protocol Encoder Block.

Dependencies

This parameter is enabled only if you select Custom algorithm option under Specify logic for checksum validation parameter.

Data Types: uint8

File path — Path of the function (.m) used for custom checksum logic

MATLAB^® path

Specify the path of the function (.m) in which you defined the custom algorithm for generating checksum bytes. The file must be saved in a directory in the MATLAB path.

Dependencies

This parameter is enabled only if you select Custom algorithm option under Specify logic for checksum validation parameter.

Data Types: uint8

Terminator — Terminator of the packet

<none> (default) | CR ('\r') | LF ('\n') | CR/LF ('\r\n') | NULL ('\0') | Custom Terminator

Specify the terminator that indicates the end of the encoded data. The last byte/bytes in the encoded output will be terminator.

If you select Custom Terminator, you can specify your own terminator value.

Custom terminator — Custom terminator of the packet

character array | array of numeric values less than 255

Specify the custom terminator that indicates the end of the encoded data. The last byte/bytes in the encoded output will be terminator.

The numeric array specified in this parameter is the uint8 integer representation of the corresponding ASCII characters.

Few examples of custom terminator values are: ‘END’, '#’.

Data Types: uint8

More About

Encode Data from Fixed-Sized Packet

The Protocol Encoder block can be used to encode input data into a fixed size packet (uint8 byte stream).

The block converts the input data into uint8 bytes as per the byte order specified, and appends the data with header, and optional checksum and terminator values.

The general structure of a fixed size packet look like this, with optional checksum and terminator fields

For example, suppose that you need to encode input into packet as specified in this structure:

In this case, you specify the block parameters as shown in the below figure. The output displayed when you simulate the model conforms to the packet structure.

Function Template for Custom Checksum Logic in Protocol Encoder Block

function csBytes = generateChecksumBytes(payload)
%#codegen
end

Create the function as specified above. The function must return checksum bytes (csBytes) as uint8 data type, whose size must be specified in the Checksum size field available in the block mask. The input to the function is the payload containing all the data bytes excluding header and terminator, as uint8 datatype.

Save the function and specify the path of the function in the File path field in the block mask. Ensure that the file is in the MATLAB path.

Monitor Signals and Tune Parameters

The Protocol Encoder block is available with Simulink^® Support Package for Arduino^® Hardware, Embedded Coder^® Support Package for Texas Instruments^® C2000™ Processors, and Simulink Support Package for Raspberry Pi^® Hardware. However, to monitor signals and tune parameters for protocol decoding in Simulink models to be run on TI’s C2000™-based targets, use the Universal Measurement and Calibration Protocol (XCP)-based External mode simulation.

Version History

Introduced in R2021b