After trying unsuccessfully to parse text-based serial data with MAX/MSP, I just hooked the disassembled mouse up to the computer and started using the mousestate object in MAX to read coordinates. Here I discovered that the “mousestate” object is constrained by the bounds of the screen. Once the mouse cursor reaches the right edge of the screen, “mousestate” no longer reports any changes. Foiled again.
I would have to return to interpreting data from Arduino. As I looked at the Arduino code that was reading from the mouse, I realized that I could simply send raw bytes from Arduino to MAX/MSP. I could simply send the x position, the y position, and then the button states in single byte transmissions. I could even make MAX/MSP handshake with Arduino after the three bytes were transferred to guarantee MAX/MSP would always receive the bytes in the same order.
Somewhere along the line I became confused, though. Somewhere along the line I convinced myself that the mouse would need to send more than a single byte of data to represent the positions. That was part of the problem, too. I convinced myself that the Arduino PS/2 mouse code was sending positions rather than position changes. Further frustration ensued.
I talked with Wendy about this feeling last week: getting entrenched in the technical and losing sight of the big picture. I told her I wanted to stop getting hung up on these kinds of problems because they make me feel angry. Nonetheless, I went down this road again and had to prove that to myself that I was capable of solving this problem.
The next time this happens, I think the best thing I can do for myself and my sense of wellbeing is to call someone up and get them to ask me questions about what I’m doing and why I’m doing it so I don’t waste time.
Ok. Ranting is finished.
Since I spent time working this problem through, I’m going to share the solution, even though it wasn’t necessary, in the hopes that someone else may benefit from it (maybe even me at some point in the future).
I was convinced I needed to send an unsigned integer for both the x and y positions from Arduino to MAX/MSP. (An unsigned integer is a positive value between 0 and 65535 which requires two bytes or sixteen bits to represent in Arduino). I wanted unsigned numbers so I wouldn’t have to deal with interpreting the negative sign in MAX/MSP. I wanted all of my data going over the serial port to always be the same length. Easy, I thought. I’ll simply break the two-byte integer into two single-byte characters and recombine them
when MAX/MSP receives them. But I don’t think very clearly when I’m trying to work out this sort of math — especially when I get frustrated.
Mouse X
MSB | LSB
16 15 14 13 12 11 10 09 | 08 07 06 05 04 03 02 01
To get the 8 Most Significant Bits, I could divide the unsigned integer by 256, which is one more than the maximum number that the Least Significant Bits could represent. The LSB portion of the unsigned integer should then be the remainder. When I worked at Crestron, Doug taught me a lazy programmer’s trick for dealing with math… Look at the extreme cases to verify that your thinking is correct.
/// Mental Interrupt ///
This blog post, while useful, is not getting me any further on things I really want to move forward on, so I’m cutting it short right here!