Lab 2 

Objective: Use interrupts and timers
                  Setup and test the tone generation hardware
                  Feasibility study on the notes and frequencies that can be computed in real time by the 8051
                  8051 Assembly language (everything will be 'C' after this)

Instructions
Note: This lab requires more thinking than coding, which is appropriate since we are doing assembly language!

1. Hook up the 8-bit D/A converter (DAC) to Port 0 of your processor. There is a reason for using port-0 that we will get to later. You will also need to use an extra pin from another port to "strobe" the digital data into the Converter. See the timing waveform on the DAC data sheet.  You can use the 8051's external memory data access capability if you want to, but this isn't necessary and we haven't covered memory mapped I/O yet. So don't worry about that! Go ahead and just use direct port operations to talk to the ADC.
2. Generate a test sine-wave tone in software and see if you can hear it on the amplified speaker. Use the audio cable that we provide to hook your player to the amp. Follow hookup directions provided by Douglas or discussed in lecture. You might want to look at the output signal with your scope to see if it looks right. Note about the lookup table: the mathematical function sin(x) evaluates to real numbers between -1 and +1, with sin(0) = sin(2PI) = 0. To come up with the lookup table for your program, you should use excel to design a sine-based function that returns values from 0 to 255, such that table[0] = table[256] = 0. Cut these values out of your excel program and install them into your code. 
3. Extend your (assembly) program to play a single three note chord using only one of the on-chip timers running at a fixed rate. Ask your musical classmates for some chords that should sound nice and look up the frequencies that correspond to the notes in the chord (search the web). Try to stay in a frequency range between 100Hz and 3KHz for the three notes of the chord. 

Turn in

• Description of your tone generation algorithm.
• Your (Well Documented) source code
• The formula that you used to generate the values in the lookup table
• List the following:
  • The three notes in your chord along with the proper frequencies for those notes
  • The timer interrupt frequency
  • The actual frequency that you generated for each of of the notes in your chord (I mean for you compute this, not measure it, show  your math out to two decimal places)
• What is the highest interrupt frequency at which you can run the timer interrupt without using up more than 90% of compute cycles in the interrupt routine, in the worst case?  This means that, out of the total number of cycles available between two timer interrupts events, all but 10% of them are used up by the interrupt service routine in the worst case (you don't have to DO this, just show your analysis).  Under these conditions, what do you expect the average utilization for your routine to be if you are running at that interrupt frequency? Note that it is not acceptable to do this:

          interrupt routine: set flag

          main: while(1) {
                          if (flag)
                              do time sensitive operations;
                              clear flag;
                       }

  In some cases, this is a fine idea, and it makes for a very short interrupt routine but in this case, it doesn't guarantee that your time sensitive operations happen on time.