FIFO Read HDRS

Read multiple ASCII data streams according to header information

Since R2020b

• 

Libraries:
Simulink Real-Time / RS232

Description

The FIFO Read HDRS block identifies and separates ASCII data streams that have embedded identifiers.

The data following a particular header can have varying lengths, but has a common termination marker such as <CR><LF>. Although you can attain this same functionality with the FIFO Read block, it requires a complicated state machine with this behavior:

• If the same header arrives in the FIFO more than once after the block was last executed, the block returns the latest instance of the header. The block catches up with data that arrives faster than the block executes.

• If a header arrives in the FIFO that does not match an item in the headers list, the block discards the message.

• If bytes arrive in the FIFO that do not match a header, the block interprets the message as having an unspecified header. The block skips these bytes.

Example models slrt_ex_serialbaseboardasciitest and slrt_ex_serialbaseboardasciisplit show how to use the FIFO Read HDRS block. To find and open these models, in the MATLAB^® Command Window, type:

modelfinder('slrealtime')

For more information, see RS-232 Serial Communication and RS-232 Legacy Drivers.

Examples

ASCII Encoding/Decoding Loopback Test

Send ASCII data over a serial link.

• Open Script

ASCII Encoding/Decoding Resync Loopback Test

Use the ability of the FIFO Read HDRS block to resynchronize after being repeatedly disabled and apply this ability to resolve errors such as when a message is only partially complete at the time the read is attempted.

• Open Script

Binary Encoding/Decoding Loopback Test

Send Binary data over a serial link.

• Open Script

Binary Encoding/Decoding Resync Loopback Test

Use the ability of the FIFO Read BINARY block to handle messages that are interrupted and only partially complete.

• Open Script

Simple ASCII Encoding/Decoding Loopback Test (with Baseboard Blocks)

Convert a single floating point number to ASCII and transmit the value over a serial link.

• Open Script

ASCII Encoding/Decoding Loopback Test (with Baseboard Blocks)

Send ASCII data over a serial link.

• Open Model

ASCII Encoding/Decoding Resync Loopback Test (with Baseboard Blocks)

Use the ability of the FIFO Read HDRS block to resynchronize after being repeatedly disabled and apply this ability to resolve errors such as when a message is only partially complete at the time the read is attempted.

• Open Script

Binary Encoding/Decoding Loopback Test (with Baseboard Blocks)

Send Binary data over a serial link.

• Open Script

Binary Encoding/Decoding Resync Loopback Test (with Baseboard Blocks)

Use the ability of the FIFO Read BINARY block to handle messages that are interrupted and only partially complete.

• Open Script

Ports

Input

F — FIFO from which to read data

serialfifoptr

Connects to the software FIFO containing data read from the serial port.

E — Enable read from FIFO

true | false

If true, read from FIFO.

Dependency

To make this port visible, set parameter Enable input.

Output

1 — Numbered output streams, one per header

vector

Vectors containing the parsed data read from the FIFO. Each output corresponds to one of the headers.

Dependency

To determine the data type of this vector, set the parameter Output vector type.

Data Types: int8 | uint8 | int16 | uint16 | int32 | uint32

Parameters

Header — Search targets in ASCII data stream

cell array of character vector

Enter the headers that you want the block to look for in a block of data from the FIFO. Enter each header in single quotes as an element in a cell array.

Programmatic Use

Block Parameter: hdr

Terminating string — Characters that end data stream

[13 10] (default) | [integer]

Enter the terminating character vector for the data. Enter the characters defining the end of character vector, typically one or two characters.

Programmatic Use

Block Parameter: nterm

Output behavior — Behavior when no new data

Zero output if no new data (default) | Hold last output if no new data

From the list, select the behavior of the block if the FIFO has not received new data:

• Hold last output if no new data — Block keeps the output from the last FIFO message.

• Zero output if no new data — Block overwrites the first element of the output with 0.

Programmatic Use

Block Parameter: hold

Enable input — Enable read from FIFO

off (default) | on

To create an input port that enables or disables the read operation, select this check box. The input port takes a Boolean signal.

Dependency

Causes input port E to become visible.

Programmatic Use

Block Parameter: enable

Maximum read size — Maximum number of characters returned by block

1024 (default) | integer

Specify the maximum number of characters for this block to return. The resulting vector size is one more than this maximum number of characters. This block indicates the number of characters being returned by using the extra element as:

• A NULL terminator for the 8-bit data types

• The character count for the 16-bit and 32-bit data types

Enter a large enough number. If this number is too small, the block cannot return anything. For example, if you enter the value 10, but on execution the FIFO contains 11 characters plus the null terminator, the block does not return any characters. If it contains 5, the block returns 5 characters plus the NULL terminator.

Programmatic Use

Block Parameter: maxsize

Output vector type — Specify output data type

8 bit uint null terminated (default) | count+32 bit int | count+32 bit uint | count+16 bit int | count+16 bit uint | 8 bit int null terminated

The 8-bit data types produce a NULL-terminated character vector in the output vector. For 16-bit and 32-bit data types, the first element contains the number of elements to expect in the rest of the output vector.

Programmatic Use

Block Parameter: outputtype

Sample time — Sample time of block

-1 (default) | numeric

Enter the base sample time or a multiple of the base sample time. -1 means that sample time is inherited.

Programmatic Use

sampletime

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2020b