FIFO Read

Read simple data streams

  • Library:
  • Simulink Real-Time / RS232

Description

The FIFO Read block is the read side of a FIFO read/write pair. It is used to parse simple data streams. The block functions in two modes, set using the Read to delimiter check box.

  • If you select the Read to delimiter check box, the block only reads elements if the specified delimiter has been written to the FIFO Write block. If the delimiter is found, the block returns elements up to and including the delimiter in the output vector. If the delimiter is not found, the block returns a zero length vector, as determined by the data type. (If you have a zero length vector, you can have your model perform a particular operation, or ignore the case.)

  • If you clear the Read to delimiter check box, the block returns elements between Minimum read size and the smaller of the number of elements currently in the FIFO and Maximum read size.

    You usually select the Read to delimiter check box when performing ASCII reads and clear it when performing binary reads.

The following are some examples of how you can set up the FIFO Read block:

  • Transmit side of the interrupt service routine — If the interrupt reason is not an empty hardware FIFO on the UART, the maximum input port receives a value of 0. If the hardware FIFO is empty, it receives the size of the hardware FIFO. The minimum input port receives the constant value of 1.

  • Receive side of the interrupt service routine — The typical case with ASCII data has the minimum and maximum input ports disabled. The Read to delimiter parameter check box is selected and the Delimiter parameter has the value of carriage return or line feed. The value of the Maximum read size parameter is large (along the order of the FIFO size) and the value of Minimum read size parameter is 1. In this form, the driver acts like a nonblocking read line.

    An alternate receive-side configuration for fixed-length binary blocks of data has the value of the Maximum read size and Minimum read size parameters set to the fixed length of the block. The Read to delimiter parameter is not selected.

For complex data streams, consider using the FIFO Read HDRS and FIFO Read Binary blocks. For guidelines on when to use these blocks, see Using the FIFO Read Blocks.

Ports

Input

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

The maximum number of bytes to return from the block.

Dependency

To cause this port to become visible, set parameter Max and Min read size ports.

The minimum number of bytes to return from the block.

Dependency

To cause this port to become visible, set parameter Max and Min read size ports.

Output

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Vector containing the parsed data read from the FIFO.

Dependency

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

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

Passes the value of port MAX through to the block that reads the ENA port.

Dependency

To cause this port to become visible, set parameters Max and Min read size ports and Enable passthrough.

Parameters

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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 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. On the other hand, if it contains 5, the block returns 5 characters plus the null terminator.

If you select the parameter Max and Min read size ports, the block interprets the value input on port MAX as the maximum number of characters to return. The actual maximum number of characters to return is the smaller of the value on port MAX and the maximum read size in the block parameters. Use this value in binary mode when the Read to delimiter check box is not selected.

Programmatic Use

Block Parameter: maxsize

Enter the smallest desired read size in bytes. The FIFO must contain at least this number of elements before elements are returned.

If you select the parameter Max and Min read size ports, the value of port MIN supersedes this value.

Programmatic Use

Block Parameter: minsize

Select this check box to enable the return of element sets that terminate with the Delimiter value. Use this parameter when working with character-based elements.

Programmatic Use

Block Parameter: usedelimiter

Enter the decimal value for an 8-bit input terminator. This parameter specifies the value on which a FIFO read operation terminates. It works with the Read to delimiter parameter. By default, this block looks for a carriage return. It only returns characters when one is found. For reference, the decimal value of a carriage return is 13, a line feed is 10.

Programmatic Use

Block Parameter: delimiter

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

When this check box is selected:

  • The value from input port MAX is the maximum number of characters to be removed from the FIFO. If this number exceeds the value of Maximum read size, the block disregards the value from the maximum input port. It takes the value of Maximum read size as the maximum number of characters to be removed from the FIFO.

  • The value from the input port MIN is the minimum number of characters the FIFO must contain before elements can be returned. This value supersedes the value set with the Minimum read size parameter.

Causes input ports MAX and MIN to become visible.

Programmatic Use

Block Parameter: enable

Select this check box to pass the value of input port MAX through to output port ENA.

Dependency

Causes output port ENA to become visible.

Programmatic Use

Block Parameter: enableout

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

Programmatic Use

Block Parameter: sampletime

Introduced in R2008a