4.4 [ mini-project ] create standard midi files with labview  (Page 2/4)

An interactive front panel is provided for each of the subVIs as an aid to your development and testing. By running the subVI with test values, you can better understand the behavioral requirements. Also, you can compare your finished result with the“gold standard,”so to speak.

Screencast videos offer coding tips relevant to each subVI. The videos assume that you are developing the modules in the order presented.

All right, time to get to work!

Midi_putbytes.vi

midi_PutBytes.vi accepts a string and writes it to a file. If the file already exists, the user should be prompted before overwriting the file.

Input requirements

• file path (file path type)
• string (string type)

Output requirements

• error out (error cluster)

Behavior requirements

• Create a new file or replace an existing file
• If replacing a file, prompt the user beforehand to confirm
• Write the string to the file, then close the file
• Connect the file-related subVIs to error out

Your finished subVI should behave like this one:

Coding tips

Watch the screencast video to learn how to use the built-in subVIs Open/Create/Replace File , Write to Binary File , and Close File . Refer to the module Creating a subVI in LabVIEW to learn how to create a subVI .

Midi_attachheader.vi

Once all of the track strings have been created, midi_AttachHeader.vi will attach a header chunk to the beginning of the string to make a complete string prior to writing to a file. The header chunk requires the MIDI file type, number of tracks, and division (ticks per quarter note).

Input requirements

• string in (string type)
• type (16-bit unsigned integer type; defaults to 1)
• number of tracks (16-bit unsigned integer type; defaults to 1)
• ticks per qnote (16-bit unsigned integer type; defaults to 120)

Output requirements

• string out (string type)

Behavior requirements

• Create a header chunk ID sub-string (MThd)
• Create a sub-string for chunk length (always 0x00_00_00_06)
• Create sub-strings for the three unsigned integers applied as inputs
• Assemble the sub-strings into a string in order as chunk ID, chunk length, type, number of tracks, and division
• Append the inbound string to the header and output this result

Your finished subVI should behave like this one:

Coding tips

Watch the screencast video to learn how to use the Concatenate Strings node to join substrings together into a single string. You will also learn how use the nodes To Variant and Variant to Flattened String to convert a numerical value into its representation as a sequence of bytes in a string.

Midi_finishtrack.vi

Once all of the delta-time/event pairs have been assembled into a string, midi_FinishTrack.vi will attach a track chunk header to the beginning of the string and append an end-of-track meta-event at the end of the string. The resulting string will represent a complete track chunk.