Noise writeback with noise+pulse on 8580 not emulated correctly

[drfiemost]

From https://sourceforge.net/p/sidplay-residfp/bugs/28/

When noise+pulse are selected the lower bits of OSC3 are being pulled down by the last four noise bits which are grounded.
See vice-emu bug #1037

Partially fixed with r2693

[drfiemost]

Still broken on 8580, see test SID/wf12nsr/wf12nsr-8580

[drfiemost]

For the record a few samplings made with exSID (pulse output is $ff)

noi	noi + pul 6581 (3884)	noi + pul 8580 (0591)
$FF	$FF	$FE
$FE	$FC	$FC
$FD	$FC	$F8
$FC	$F0	$F8
$FB	$F8	$F0 / $F4
$FA	$F0	$F0 / $F4
$F9	$E0	$F0
$F8	$E0	$F0 / $F4
$F7	$F4	$EC / $E0 / $E4
$F6	$F0	$EC / $E4
$F5	$80	$EC / $E4
$F4	$80	$EC
$F3	$80	$E4
$F2	$80	$EC
$F1	$80	$EC
$F0	$80	$E0 / $E4
$EF	$00	$DC
$EE	$00	$DC / $DE
...	$00	...
$C4	$00	$30
$C0	$00	$30
...	...	...
$23	$00	$00
...	...	...

[drfiemost]

Still broken on 8580, see test SID/wf12nsr/wf12nsr-8580

For the record only the wave 0xc test fails:

got (with reSID)
ff fc fc f8 f8 f8 f8 f0 f0 e0 e0 e0 e0 ...
   ^^ ^^

expected
ff f8 f8 f8 f8 f8 f8 f0 f0 e0 e0 e0 e0 ...

[mrdudz]

So, since residfp is in VICE now, i have also switched the testbench to it - these are the still failing tests.

for 6581

../SID/wb_testsuite/ noise_writeback_check_8_to_C_old.prg - error  
../SID/wb_testsuite/ noise_writeback_check_9_to_C_old.prg - error  
../SID/wb_testsuite/ noise_writeback_check_A_to_C_old.prg - error  
../SID/wb_testsuite/ noise_writeback_check_C_to_C_old.prg - error  
../SID/wb_testsuite/ noise_writeback_check_D_to_C_old.prg - error  
../SID/wb_testsuite/ noise_writeback_check_D_to_E_old.prg - error  
../SID/wb_testsuite/ noise_writeback_check_E_to_C_old.prg - error  
../SID/wb_testsuite/ noise_writeback_check_F_to_8_old.prg - error  
../SID/wb_testsuite/ noise_writeback_check_F_to_C_old.prg - error

and for 8580:

../SID/wb_testsuite/ noise_writeback_check_C_to_9_new.prg - error  
../SID/wb_testsuite/ noise_writeback_check_C_to_E_new.prg - error  
../SID/wb_testsuite/ noise_writeback_check_C_to_F_new.prg - error  
../SID/wf12nsr/ wf12nsr-8580.prg - error  

No idea how reproducable these even are on real chips - as always i am open for suggestions so we can produce better tests :)

[drfiemost]

Yeah, fixing some test breaks other, I don't know if tests are unreliable or there is something I'm missing.
Maybe I should get a C64U and play around with combined waveforms...

[Toddler-Boy]

I would be willing to donate one.

[drfiemost]

Thanks for the offer but I don't want to commit to any serious work.
I may get back at this but no guarantee.