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Hermit
Registered: May 2008
Posts: 208 |
Proposal for 2SID hardware-compatibility
I'm fiddling with 2SID hardware solution right now, and got an idea for a most suitable address for the 2nd SID, which could be compatible with almost all hardware solutions (except $de00, $df00, but they're not good selection anyway due to conflicting with AR,TFR, etc. cartridges.)
In VICE it's easy to set 2nd SID base-address, but it's not the case with real C64.
There's a multiplexer circuitry, which uses one of the address lines between A5..A9 ($20..$200) beside the original $d400..$d7ff chip-select signal. The address-line is hardwired in most of the cases, and not easily selectable/switchable in the real machines.
(Btw. I could solve it by hardware to see 2nd SID both in $d420 and $d500 locations, by "OR"-ing A5 and A8 lines...)
I think using/preferring only base-address $D7E0 for 2nd SID in 2SID programs & music releases would ensure that any of the A5..A9 address lines could select the 2nd SID in the machines, similarly to an "OR" function...
(the address came from this simple calculation: $d400+$20+$40+$80+$100+$200 = $D7E0)
It's easier by software than by hardware.
And VICE's 2nd SID address can be set to $D7E0. If VICE emulates the hardware multiplexor, the $d420, $d500, etc. settings could be fine too in VICE, just as on real C64, all would call 2nd SID at $d7E0
I guess it's not hard to configure in SID-players too...
Just, because 2SIDs seem to get more popular and real machine is always better to compose & listen with :)
Maybe the issue, it's not forward-compatible with 3SID, 4SID, etc solutions.
A further improvement to this 'specification' could be to distinguish mono (6 channels) vs stereo (2x3 channels) SID tunes by the A6 or A7 ($40 or $80) address lines, which seem rarely used for 2nd SID selection...
So in that case SID addresses could follow like this:
$d400..$d41f: 1st SID
$d7a0..$d7bf: 2nd SID, A6 ($40) low - line says "mono"
$d7e0..$d7ff: 2nd SID, A6 ($40) high - line says "stereo"
It was just a idea, i couldn't find this in the forum after some search, maybe it was mentioned before, maybe not... |
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SIDWAVE
Account closed
Registered: Apr 2002
Posts: 2238 |
Hermit,
you should ask my brother Devia about this, because he and Lotus have made what i think is the ultimate 2sid.
The 2sid that Devia has done, and there is a whitepaper on it, you just plug it on, and go! no soldering, no wires.
Devia and Lotus showed it on LCP 2009 party, but people arent interested to invest money in it, so it was never produced.
naybe youre doing it a bit different, and want a programmable sid address for sid #2 ?
write to devia, ulf@harries.dk |
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SIDWAVE
Account closed
Registered: Apr 2002
Posts: 2238 |
using d420, d440, d480, d4c0 etc for 2nd sid seems best to me, because all the software that use 2 sids, use one of these adresses.
going d7xx seem weird, then all this software is obsolete! :) |
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chatGPZ
Registered: Dec 2001
Posts: 11350 |
actually there is a lot of software that uses $de00 =P |
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Hermit
Registered: May 2008
Posts: 208 |
@SIDwave: The $d7e0 address would trigger all of the mentioned $d420, $d480, etc. addresses with the simple multiplexer solution (like my transistor-based solution). So the old programs mustn't be modified...it's just about new programs to be more compatible with existing hardware...
If there are multiplexers which strictly use certain ranges (e.g. $d420..$d41f and no repeated address), this wouldn't work...
@Groepaz: I like to use fastloader cartridge even if I have 2 SIDs in my machine. I remember my first home-made cartridge, it didn't need the $de00 address and worked with $DE00 SID, but for example, an Action Replay cartridge and the MMC Replay clashed with $de00 IIRC... If it's the case, that's not good if $de00 is used a lot...
I checked: In the shematic of Action Replay cartridge the IO1 ($de00) and IO2 ($df00) (pin 7 and 10 of the expansion port) are connected and used/occupied :(
http://www.zimmers.net/anonftp/pub/cbm/schematics/cartridges/c6.. |
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tlr
Registered: Sep 2003
Posts: 1787 |
Quote: Watch out for the VDC which naturally resides at $D600 in C128, even in C64 mode. Something like that should detect the VDC reliably:
LDX #$12
LDY #$DE
LDA #$0E STA $D626 STX $D627
LDA #$0F STA $D626 STY $D627
LDA #$0E STA $D626 CPX $D627 BNE novdp
LDA #$0F STA $D626 CPY $D627 BNE novdp
This writes 2 values into VDP registers that won't cause havoc (cursor position) and then checks whether these values can be read back.
If a SID is connected instead it'll read from voice 3 osc which will never give such values since its maximum envelope speed is limited.
Thanks for pointing that out. $d626/$d627 would be offset 6/7 in a sid (=V0SR + V1FL). Those are write only and unpredictable on read.
Do I understand correctly that the VDC registers are mirrored every 2 bytes in $d600-$d7ff?
Detecting $de00-$dfff sids is a bit more tricky because of unknown types of carts potentially residing there.
A selection of Scan, Partial Scan (e.g $d400-$d5ff) and manual would be appropriate IMO. |
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Kabuto
Account closed
Registered: Sep 2004
Posts: 58 |
I read incorrect values from a SID register table written in decimal (instead of hex), sorry :(
And yes, the VDC's 2 external registers repeat again and again from $D600 to $D6FF.
Also, check for further SIDs at $D700 in C128.
Here's a corrected version:
; Disable voice 3 by setting the test bit if there's a SID reachable at $D600. This should ensure that reading the oscillator always yields the same value.
LDA #$FF
STA $D612
; Write test values into VDC's cursor address and read them back.
; If there's a SID it'll read voice 3 osc instead and thus get different values.
LDX #$12
LDY #$DE
LDA #$0E STA $D61A STX $D61B
LDA #$0F STA $D61A STY $D61B
LDA #$0E STA $D61A CPX $D61B BNE novdp
LDA #$0F STA $D61A CPY $D61B BNE novdp |
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tlr
Registered: Sep 2003
Posts: 1787 |
Another approach would be to detect the fact that the machine is a C128 and skip the $d600-$d6ff area based on that. (or always skip $d600-$d6ff because it's presumably rare as sid placement)
C128 can be detected in a couple of ways. I'm tempted to try the 1/2 MHz variant. i.e switch on 2 MHz in the vb area and verify cpu timing against a cia timer.
Does 2 MHz mode affect the VIC output at all if kept in the upper/lower border? |
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Oswald
Registered: Apr 2002
Posts: 5086 |
sure, if you open the borders, then instead of $3fff always the (every 2nd) byte is displayed that the cpu read last. risen from oblivion exploited this to display fullscreen & top / bottom border gfx. (hint: many lda #$xx). |
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tlr
Registered: Sep 2003
Posts: 1787 |
Quoting Oswaldsure, if you open the borders, then instead of $3fff always the (every 2nd) byte is displayed that the cpu read last. risen from oblivion exploited this to display fullscreen & top / bottom border gfx. (hint: many lda #$xx).
Ah, neat effect! For this job I only need to be sure it doesn't f-ck up the video output when flipped in the upper/lower border. I seem to remember that the display goes grey/bw when keeping the 2MHz mode permanently on but it was a _really_ long time since I had a C128 to fiddle with. |
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Kabuto
Account closed
Registered: Sep 2004
Posts: 58 |
Quote:Does 2 MHz mode affect the VIC output at all if kept in the upper/lower border?
No.
You're totally right - it should be enough to test whether you've got a C128 and then exclude $D500..$D6FF.
But you don't need to do timing tests - write $00 to $D030 and then read it back, AFAIK you'll then always get $FF on C64 and $FC on C128.
However, there might be unconnected address ranges (e.g. if a 2-SID addon was installed but just 1 SID inserted into it) - you'll get nonsense (more or less) when reading from those values (to be precise: remnants of the data byte read by the VIC during its cycle phase, with 0 or more bit flips). |
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