Component: Circular Buffer (Storage)

Author	Matrix Ltd
Version	1.5 (Release)
Category	Storage

Circular Buffer component

Circular buffer component allowing easy and efficient first in first out (FIFO) style data byte storage. Useful when used with a comms component to capture data as it comes in ready for processing when we have time. Also features macros to allow you to check for specific incoming responses such as "OK" or "ERROR".

Examples

Basic Example

Circular Buffer Example File demonstrating the storage and retrieval of data. CircularBuffer System panel showing data in and data out of the FIFO circular buffer.

Console window showing data in the circular buffer on the first simulation run.

Console window showing data in the circular buffer on the second simulation run, note that the start location has been shifted and will eventually wrap hence the name, circular buffer.

Keypad Based Door Entry System

Each key press on the keypad is fed into the Circular Buffer component. We then poll the buffer to see if the correct characters for the password have been entered. Keypad Door Entry If the correct sequence is detected then we activate the solenoid component for 5 seconds.

Reliable Communications Data

This example takes bytes received from the Serial UART and uses the circular buffer to store the bytes as they come in using an interrupt. The main routine then forwards the bytes through to a PC using a USB serial connection. This example would work equally well for creating a bridge between several UARTs or translating Serial to SPI or I2C etc. UART to USB Serial Data Bridge

AT Command Responses

This example sends out AT commands to an AT based communications module e.g. GSM or Bluetooth. The response from the module is stored in the circular buffer and we then scan the buffer for appropriate responses from the module. The outcome of the command is then printed to the LCD to let you know if the command was accepted, caused an error or simply timed out. Reliable AT Command Response

Searching for none ASCII characters

The LookForValue and WaitForValue functions can be useful when searching for ASCII data in the circular buffer. You can also use the escape sequence \x to search for hexadecimal values in the buffer.

e.g. "ABC\xFF\x80"

Will look for the ASCII characters A,B,C followed by the byte values 255 (0xFF) and 128 (0x80).

Downloadable macro reference

LookForValue

Scans the buffer for an array of specific values.

Returns 0 if the value is not found.

Returns 1 if the value is found.

Parameters

<- STRING Value

Value to look for, can be a string or byte array,

This parameter may be returned back to the caller

BYTE NumChars

The number of characters you wish to try and match

BYTE RemoveContent

0=Leave data alone, 1=Remove data from buffer

BYTE ResetFind

0=Continue the find from the last operation, 1=Start again

Return value

BYTE

GetIndexedByte

Gets the value of a single byte at a known location in the buffer.

Leaves the buffer contents and pointers untouched.

Parameters

UINT address

Return value

BYTE

WaitForValue

Waits for an array of values to appear in the circular buffer.

Returns 0 to indicate a timeout.

Returns 1 to indicate the data has been found.

Parameters

<- STRING Value

This parameter may be returned back to the caller

BYTE NumChars

Number of characters to try and look for

BYTE RemoveContent

0=Leave the buffer contents untouched, 1=Remove values as you go

UINT Timeout

Max amount of time to wait in milliseconds before returning 0=WaitForever

Return value

BYTE

GetNumberBytes

Returns the number of valid data bytes currently inside the buffer.

Parameters

This macro has no parameters

Return value

UINT

PeekByte

Reads the next available byte from the circular buffer without advancing the current index,

Returns 255/512 if the buffer is empty.

Parameters

This macro has no parameters

Return value

UINT

PutByte

Add byte to the next free location inside the circular buffer.

If the data goes into the buffer correctly then return 1.

Otherwise the buffer is full and the return value will equal 0.

Parameters

BYTE Data

Return value

BYTE

GetByte

Reads the next available byte from the circular buffer,

Returns 255 if the buffer is empty.

Parameters

This macro has no parameters

Return value

UINT

FlushBuffer

Clears the contents of the buffer and re-initialises the index locations.

Parameters

This macro has no parameters

Return value

This call does not return a value

Simulation macro reference

GetConsoleHandle

Gets the handle to the console allowing data displaying on the panel etc.

Parameters

This macro has no parameters

Return value

HANDLE

Property reference

Buffer Size

This property is of type Unsigned integer and can be referenced with the variable name BufferSize.

Sets the number of byte elements inside the circular buffer.

Storage Type

This property is of type Fixed list of ints and can be referenced with the variable name StorageType.

When buffer is full this property decides what to do.

Store first x values - Will retain the information inside the buffer, new data will be discarded.

Store last x values - Will discard the oldest location in the buffer and overwrite with new data.

Memory Type

This property is of type Fixed list of ints and can be referenced with the variable name MemType.

No additional information

Return Type

This property is of type Fixed list of ints and can be referenced with the variable name RETURN.

Specifies the way the receive function indicates a timeout.

8 Bit mode - Timeout is represented by the value 255.

16 Bit mode - Timeout is represented by the value 512 allowing the value 255 to represent valid data