#54670 - Ultima2876 - Wed Sep 21, 2005 2:48 pm
What kinds of speeds can be expected with the multiplayer? I'm sure I heard somewhere that you can reliably send/receive about 20 bytes of data per frame, with all other matters taken into account, in multiplayer mode. But isn't multiplyer mode 115000 kbps? Wouldn't that suggest that we could send a hell of a lot more than 20 bytes/frame?
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#54677 - FluBBa - Wed Sep 21, 2005 3:55 pm
Well, you'd probably want a game in there as well and not just a serial transfer application?
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#54690 - Ultima2876 - Wed Sep 21, 2005 5:56 pm
Yeah, but why would that make a difference to the transfer speed? Or is your point that the game makes the biggest difference, and that the transfer speed isn't really the limiting factor?
#54699 - thegamefreak0134 - Wed Sep 21, 2005 7:17 pm
I'm under the impression that the transfer speed takes a certain % of CPU time per frame depending on what you are sending. I think first of all that it is up to you to code the multiplayer game around the stuff you need to send. If the game is choppy on the real hardware (or choppy when the emu runs at 100%) then either cut back on data sent or cpu time of the game.
Other than sending custom stuff such as images and sound for a multiboot game, it doesn't seem like you should really have to worry about it that much anyway.
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#54713 - Miked0801 - Wed Sep 21, 2005 10:00 pm
Multiplayer :P
Ok, the problem with MP on GBA is that it has zero, zip, none, nada in the way of error checking or packet handling. Also, since it is run via interrupts, it can get in the way of other interrupts as well. Also, DMA will cause packets to be missed occasionally.
So, you need to write a whole bunch of error checking/packet handling code to get reliable communications between GBAs and it's this code that eats up your cycles. MP code on GBA is extremely difficult to do correctly.
#54726 - Ultima2876 - Wed Sep 21, 2005 11:11 pm
Hmm... about that - with the loss of packets... is it only loss of packets, or do you have to deal with corrupt packets aswell? (as in, receiving YYYY instead of XXXX due to line noise or what-have-you)
#54788 - tepples - Thu Sep 22, 2005 4:01 pm
Yes, line noise is rare but possible. Put some sort of CRC on each game cycle's transmission.
And yes, you do want to code a serial transfer tool sometimes, to load the next level of a multiplayer game.
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#54799 - Miked0801 - Thu Sep 22, 2005 6:11 pm
As Tepples stated, corrupt packets occur regularly as well. More often with DMAs/Interrupts screwing with a transmission that actual line noise, but line noise does occur as well.