Re: LMC1992/Microwire test WAS: [hatari-devel] No sound in the Pacemaker Demo

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

Le 04/06/2014 23:45, Konador, Cyprian a écrit :
> Hi David,
>
> Ops, it seems that you caught me. I should completely remove Set-up LMC1992 section, because it interferes my test... Thanks for that hint.
> Ok, I'll check your code and also I'll redo my tests. Unfortunately I have to wait with those tests until tomorrow evening.
>
> BR
> Cyprian

Hello

I agree with David on the way bits are shifted in the microwire. If we 
want to set mixer to 1, then we must send 10 000 000001 ; assuming we 
could send bits in a non-consecutive stream (which we can't, see below), 
then we would need to send a data value with at least to "1" bits 
(depending on the mask). But $8000 has only one "1" bit, so I don't see 
how we could get the 10 000 000001 sequence anyway.

Most probable thing is that the $8000 is ignored and LMC keeps its 
previous mixer value set by TOS, which is "1".

Another test would be to run cyprian's program that set mixer to "0" 
just before starting the HD version of the demo. I think in that case 
there would be no sound in the demo.


As for the serial protocol, as David noted in another post, the 
datasheet for LMC1992 tells that :

"When the ENABLE line is low, data can be serially shifted from the 
controller to the LMC1992. As the ENABLE line goes through the low-to 
high transition, any additional data is ignored. Data present in the 
internal shift register is latched and the instruction is executed"

This means the mask should contain 11 consecutive "1" bits, but they can 
be at any position.


But I think we should blame Atari for this error ; the STE addendum doc 
at http://dev-docs.atariforge.org/files/STE_Dev_Add_5-25-1989.pdf gives 
several examples which are wrong (only the first 3 are correct, the 2 
others are wrong because they include "0" bits in the mask before the 3 
data bits are received)


Let us know what result you get after redoing your tests.

Nicolas