VDP detailed access timing diagram

بواسطة PingPong

Prophet (4093)

صورة PingPong

29-06-2010, 21:41

http://www.smspower.org/uploads/Development/1978_9918_Master_Timing_by_Serigio_Maggi.jpg

in all modes, show the time used for ptr fetching / color fething / name table fetching / cpu access / sprites...

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بواسطة ARTRAG

Enlighted (6923)

صورة ARTRAG

29-06-2010, 23:29

humm, not easy to be deciphered ...
It si not clear to me if snippets in the other posts
http://www.msx.org/forumtopicl11279.html
can work in the active area or thay are too fast

بواسطة PingPong

Prophet (4093)

صورة PingPong

30-06-2010, 09:44

humm, not easy to be deciphered ...
It si not clear to me if snippets in the other posts
http://www.msx.org/forumtopicl11279.html
can work in the active area or thay are too fast

yes, is not so clear.

another common unclear thing is follow:

the SMS says about a trick that can be used to point the vram ptr by writing only the lower byte of address then outing on data port.

;assuming the vram ptr is pointing to 0x1000...
ld a,0x20
out (0x99),a
nop
nop
....
ld a, 0x10
out (0x98),a

should poke the 0x10 value into location 0x1020

initially i thought this as a SMS VDP 'feature' but on the site there is nothing that say 'does not work on SG-1000'. the SG-1000 has the TMS vdp, not the sega VDP.

however, i suspect it does not work. to do a real test i think one should try on a msx1 with TMS (i suspect V99x8 does not have this feature )

بواسطة SLotman

Paragon (1242)

صورة SLotman

30-06-2010, 10:06

And another note: I don't know if it is the TMS on SG-1000, SG-1000 internals or what - but the VDP on SG-1000 is actually faster than on MSX. I recently ported a game (to be released soon, on MSX Files 11th anniversary) and just by swapping the SG-1000 ports for MSX ones (BE/BFh -> 98/99h), the game ran much slower than the original...!

So who know if those times can be applied to MSX also... :/

بواسطة hap

Paragon (2042)

صورة hap

30-06-2010, 13:07

PingPong: yes, that's known to work on MSX1 VDP.
SLotman: MSX Z80 is slower than the one in SG-1000 or ColecoVision.

بواسطة SLotman

Paragon (1242)

صورة SLotman

01-07-2010, 08:17

SLotman: MSX Z80 is slower than the one in SG-1000 or ColecoVision.
Are you sure about that?

Both according to Wikipedia, Retrogaming and SMS Power docs, SG-1000 has a 3.57-3.58Mhz Z80, just like MSX...

At least with the game I converted, the slowdown is caused on a routine that writes tons of sprites on screen - and just by disable the writes the game runs at full speed. That's why I tought the VDP must be faster on SG-1000 than on MSX... maybe less or no waitstates?

بواسطة PingPong

Prophet (4093)

صورة PingPong

01-07-2010, 10:34

At least with the game I converted, the slowdown is caused on a routine that writes tons of sprites on screen - and just by disable the writes the game runs at full speed. That's why I tought the VDP must be faster on SG-1000 than on MSX... maybe less or no waitstates?

Ah, ok, if you disable the writes the speed will benefit of course! Question

in all msx models except turbor there is no hw that make the z80 wait while talking with vdp.
the only reason of slowdown maybe that on sms there are no wait states?

Plus i've the feeling that SMS programmers never do screen updates outside VBLANK. so probably they never got the vdp data corruption when writing too fast on vdp.

بواسطة hap

Paragon (2042)

صورة hap

01-07-2010, 14:53

yes i am sure about that SLotman, you forgot about MSX Z80 M1 wait state?
*inserts plaatsvervangende schaamte*

بواسطة SLotman

Paragon (1242)

صورة SLotman

01-07-2010, 17:28

yes i am sure about that SLotman, you forgot about MSX Z80 M1 wait state?
*inserts plaatsvervangende schaamte*

Ah, ok - I thought you meant clockwise SG-1000 had a faster Z80 Wink