使用Arduino发送MIDI SysEx消息？

Question

I would like to send a MIDI SysEx message like this to my Roland JX8P Synth.

F0 41 36 06 21 20 01 22 1B F7

This message would alter the VCF cutoff frequency of the synth. 1B is a variable hexadecimal value, swinging from 00 to 7F, relative to cutoff frequency.

In the MIDI library I've found the documentation for sending a SysEx message.

sendSysEx (int length, const byte *const array, bool ArrayContainsBoundaries=false)

From what I can tell bool ArrayContainsBoundaries specifies whether or not you want the library to include the F0 and F7 message start/stop tags (I don't so I'll set it to true). Int length denotes the message length in bytes(my message is 10 bytes, so this will be 10).

What I'm confused about is the array. Instead of storing all the values in the array can I just specify them like this?

 MIDI.sendSysEx(10,0xF0 0x41 0x36 0x06 0x21 0x20 0x01 0x22 0x1B 0xF7,true);

Also, is adding the prefix 0x the correct way to specify the bytes here?

Answer 1

The basic answer is "no":

Your sendSysEx() function is looking for take two or three parameters:

• Length
• The array of data
• The flag whether the array contains boundaries or not. This one is optional: if you omit it the parameter will be treated as false

By trying to pass your array data like this:

MIDI.sendSysEx(10,0xF0 0x41 0x36 0x06 0x21 0x20 0x01 0x22 0x1B 0xF7,true);

You are doing one of two things:

• As written above, it is just a syntax error: the compiler doesn't know how to parse the list of numeric literals not separated by anything.
• If you separated the items by a comma, the compiler says "Oh, he is passing 12 parameters. Let me look for a function that takes 12 integer parameters... oh, I don't have one. Sorry." That gives your no matching function for call to error.

So, one way to call your function is like this:

byte data[] = { 0xF0, 0x41, 0x36, 0x06, 0x21, 0x20, 0x01, 0x22, 0x1B, 0xF7 };
sendSysEx(10, data, true);

In C++11 you can get closer to what you want by initializing the list in the function call, something like sendSysEx(10,{0xF0, 0x41, 0x36, 0x06, 0x21, 0x20, 0x01, 0x22, 0x1B, 0xF7}, true); , however, you'll find that might run into another problem (depending on your toolchain): the compiler may assume that your initializer lists like that are lists of int s, not byte s, which will also cause a compiler error, unless you specifically told your compiler to assume integer literals to be 8 bits.