[Coco] more 1 bit madness

[Simon Jonassen]

Hi Steve...

Did u access the AY chip on the SSC directly or via the buffers provided by
the PIC ?

/Simon :-)
 

-----Oprindelig meddelelse-----
Fra: coco-bounces at maltedmedia.com [mailto:coco-bounces at maltedmedia.com] På
vegne af Steve
Sendt: 21. januar 2014 17:48
Til: CoCoList for Color Computer Enthusiasts
Emne: Re: [Coco] more 1 bit madness

Simon,
Never needed to poll the speech sound pak since I used the v-sync Interrupt
to feed information into it at the right time. (Changing the 3 "voice"
channels of the Sound FX chip.)  I never used the speech side of the cart in
my games.

By the way, the SSP used a General Instrument AY-3-8910 sound chip.
See: http://en.wikipedia.org/wiki/General_Instrument_AY-3-8910

This chip was widely used in the Video Game industry.  From Arcade Games to
the Vectrex, I've written quite a few games using it.  I even produced a 6
Voice (2 chip) version called Hard Music for the TRS-80 I/III.  This was a
follow up to my software only "Soft Music" that played two voices
simultaneously in tune.  A first for any home computer just using software
to pull it off.

The key to Soft Music keeping both voices in turn was running both delays in
the same loop.  How do you do that?  Use mathematics to create the timing.

Your non interrupt version of the code used a simple time delay to trigger
the flip the it event.  My code used the addition of a number to the sum
register to trigger the flipping the bit.  In the case of the 6809, I would
load up the SUM value into the D register and add its tone number to it.
(and save back the sum.) When there was an overflow (carry bit set), the
sound bit was flipped. (Did a xor $80 or $40 depending on the voice.)  After
doing one voice, the code would working the second voice in the same loop.
The loop was coded so the flipping or not flipping of the audio bit took the
same number of cycles.

Changing the Tone Number that was added to the sum would create the note at
the right tone without effecting the other note.  This process was also a
auto-tuning. If the delay for a bit flip was not right on the money because
of the resolution of the loop, each pass would adjust
(above/below) to the right frequency to keep the note in tune. (The number
still in the SUM after an overflow did the tuning.) Very important for the
higher musical notes.

As with your first demo, this code took 100% of the CPU time to pull it off.
That's why this code was limited to the Title Page in my games.  
But it did play a very pleasing two note harmony in a 6 octave range.

Steve

On 1/20/2014 11:14 PM, Simon Jonassen wrote:
> See, the SSC makes things a heck of alot easier....
>
> Especially if you program it in direct mode.....
>
> The only downside is having to poll it to see if it's ready for more 
> input
>
> /Simon :-)
>   
>
> -----Oprindelig meddelelse-----
> Fra: coco-bounces at maltedmedia.com 
> [mailto:coco-bounces at maltedmedia.com] På vegne af Steve
> Sendt: 21. januar 2014 07:35
> Til: CoCoList for Color Computer Enthusiasts
> Emne: Re: [Coco] more 1 bit madness
>
> May folks out there may not know that a large number of CoCo games did 
> support the speech sound pak for better music and sound fx.  It also 
> has the advantage of speeding up the game a bit too.
>
> Steve
>
> On 1/20/2014 10:24 PM, Nick Marentes wrote:
>> Steve <6809er at ...> writes:
>>
>>> Tandy did put a 3-voice sound chip in CoCo,  the never released 
>>> Deluxe Color Computer that would sold for twice the price of the CoCo 2.
>>>
>>> But that's the problem.  Adding stuff like that would add to the 
>>> cost of the computer.  The only reason we got the CoCo 3 was its 
>>> build cost lower that the CoCo 2.
>> This is definetely the case.
>>
>> What may have also swayed them away from providing sound is that 
>> Tandy sold a sound and speech cartridge. They probably thought 
>> "There's your sound chip!" and "we can profit by selling that as an 
>> add-on expansion" (along with a multi-pak!).
>>
>> With Tandy it was always about money. Keep costs down and profits up.
>>
>> Nick
>>
>>


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