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One of my first goals for the RCX was to try and get it to speak. I talked
to Markus about this a long time ago. At the time, he had written the
speaker driver but was unable to get much more than noise to come out of
it. Perhaps the digital resolution of the speaker is such that it can only
produce beeps.
I would be very interested if you can get it to do more than beep.
At 04:15 AM 11/25/99 +0000, you wrote:
> hello again,
> has anybody got anything else than noise from legOS 0.2.2 dsound_play ?
>
> i'm able to compile and dll this little application:
>
> #include <dsound.h>
> #include "sample.h"
>
> int main(int argc, char *argv[])
> {
> dsound_play(sample,sizeof(sample));
> return 0;
> }
>
> ( sample.h was produced by running : sample-convert fuenfte.wav )
>
> However, everything i hear when i press RUN is a short burst of noise.
>
> What i'm wondering about: as far as i understand currently, dsound_play
> works as follows:
> 8-Bit-Timer0 (whose output is wired to the speaker ?) is programmed to
> output 1 on compare A match, and 0 on compare B match. IRQ is enabled on
> A match, and the IRQ handler puts a new sample into compare B register
> on every 4.th interrupt. The level of A match is fixed to 0xff-20 = 235
> ( maybe the speaker needs some DC ??).
> Timer base frequency is set to system/2 making 8 Mhz, what results in
> 8000000/256 = 31250 IRQ frequency. Because only every 4.th interrupt
> gets a new sample, actual playback frequency is 31250/4 = 7812.5,
> approximately 8000.
> Thus, the average voltage that is output to the speaker will be
> following the samples, as long as the value of the samples won't exceed
> 235. However, the converted sample.h contains many values larger than
> 235, so i think this can't work.
> Thanks for any hints (or a .wav file that plays nicely), Martin
Joel Shafer joel@connect.net
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