Change PWM period

The PWM period is 1.3 ms by default (about 770 Hz). In order to change the period, you can just adjust the values in line 138 of au_plus_top.luc (or corresponding line for the Cu FPGA):

pwm pulsewm[NUM_PWM](#TOP(254),#DIV(9),#WIDTH(8));

As specified by Alchitry, the TOP and DIV are responsible for the period in the following manner:

If you need a specific period (i.e. for servos),
you can use DIV to divide the clock in powers
of 2 and TOP to set the max value.

If TOP is 0, 2^WIDTH is used for TOP.

Note that if WIDTH isn't big enough to store the
TOP value, TOP will never be reached and 2^WIDTH
will be used instead.

The duty cycle is: TOP / value
The period is: TOP / (CLK_FREQ / 2^DIV)

For a servo, you typically want a frequency of
50Hz, or a period of 0.02 seconds. With a
clock frequency of 50MHz, you should use
TOP = 244, DIV = 12, and WIDTH = 8. If you
want more resolution you can use
TOP = 62500, DIV = 4, and WIDTH = 16.

Where CLK_FREQ is 100 MHz.

For instance with a 8 bits WIDTH (see the other PWM tutorial for how to changed the bit depth): | TOP | DIV | Period | | :—: | :-: | :——: | | 250 | 2 | 0.01 ms | | 156 | 6 | 0.1 ms | | 254 | 9 | 1.3 ms | | 244 | 13 | 20 ms |

1. Change the TOP and DIV values.
2. Recompile the code and upload it to the FPGA.