Getting Started

Chapter 8: C Pointers and Arrays

sion of the definitions:

le, 0};

actual

fi it and

that I have the time or the skill. In

in C we sometimes have to dance lightly around

: we equate a constant integer pointer pointer to a cast

function pgm_read_word, which takes as a parameter

g element of the Songs[] array. What we are doing is

a function that knows how to extract a pointer to Flash

cated... but so what, it works.

the song table in the Timer1 Input

is case is used to set the counter top value.

taken from the Butterfly code and are based on a cpu clock

of 2 MHz for the USART,

ut do not truly compensate for the difference.

equency for

fo owing a. For

First look at his ver

// pointer-array with pointers to the song arrays

const int *Songs[] PROGMEM = { FurElise, Mozart, Minuet,

AuldLangSyne, Sirene1, Sirene2, Whist

const int *pSong; // mt point to a ram location (pointer array

Songs)

The __flash of the IAR compiler is replaced by the PROGMEM. And the
use is as follows:

// mt pSong = Songs[song]; // point to this song

pSong=(int*)pgm_read_word(&Songs[song]); // looks too

complicated...

Yep, I agree: ‘// looks too complicated', but I have no intention to try to x
make it look more C-like. I doubt seriously
programming microcontrollers
ANSI C and use what works.

What the statement says is
of an integer pointer of the
the address of the son
sending this address to
RAM. Looks too compli

Setting the frequency

Tones are setup by putting an integer from
Capture Register 1, ICR1, which in th
The values are
running at 1 MHz. Since we are using a cpu clock
adjustments are made that help b

We select a base frequency of 220Hz (the A note) and calculate the fr
subsequent notes using the notes position on the musical scale ll
instance, C0 is 3 after A: