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is the b-bus only 16bits?

Coolgame - Nov 23, 2011

		Coolgame		Nov 23, 2011
			the sh2 system bus runs at 32bits while the b bus runs at 16bits(multiplexed). wouldn't that be a problem in transmitting 32bit data from sh2 to either vdp 1 or 2? what would happen if you try? is there any way to over come this? I hope i'm looking at it wrong.

		antime		Nov 23, 2011
			32-bit accesses are transparently split up into two 16-bit accesses. This is something you only really need to worry about if you have shared data (eg. a 32-bit variable accessed by both a SH2 and the M68000 needs some sort of guard lock).

		Coolgame		Nov 23, 2011
			oh no,that's not really what i wanted to ask, i know i ask it but, it's like this, what if i wanted to do some sort of 3d transfomation that require 32bit vertices animation using the b-bus at full 28mhz speed (with 60 frames per second)? in other words a better way to put it, what if a 32bit program is running on the b-bus a full speed? would that mean you can only use half that or you can only run a 16bit program on the b-bus at 28mhz?

		antime		Nov 23, 2011
			The answer is the same. A 32-bit access will take two bus cycles (plus any wait states added by bus arbitration).

		Coolgame		Nov 23, 2011
			well i kind of figure that but if that's the case is there another way around the b-bus? do any other buses go to the vdp 1 and 2? like the the system bus?

		antime		Nov 23, 2011
			No, do you expect this to be an issue for you?

		Coolgame		Nov 23, 2011
			antime said: do you expect this to be an issue for you? no, at least not much unless there's any slow down when acessing vdp 1 and 2 vram at the same time and will it add more stress if i use the dsp to do vertice transformation math. if i like to use 3 or 4 resources (sh2,vdp 1 and 2 the scu's dsp) will there be a issue?

		antime		Nov 23, 2011
			That depends on how much data you want to transfer, but probably not. VDP1 is much more likely to be fillrate limited (which also limits the amount of vertices processed), and for VDP2 you usually just update some registers once per frame and maybe some tilemap data.

		Coolgame		Nov 25, 2011
			yeah, in that case i have to find a way to cope with that fact. im learning alot about the saturn (no more coding contests?). sometime around this december im buying a new modchip, these emulators is not cutting it. maybe that's it about the b-bus for now. being how it's structure a effective graphic engine is needed. but in that case can the dsp math chip do Gouraud shading or pre clipping? when they say it can do lighting calculation in what way? has it been use before?

		antime		Nov 25, 2011
			You'll gain the best insight of the SCU DSP's capabilities by reading the SCU manual and the tutorial tech note (SOA-8). Its main strength is performing series of single-cycle multiplications, and if you can't keep the multiplier busy the work is probably better performed on one of the main CPUs (the SCU DSP instruction set is awkward for more general-purpose programming, and the clock frequency is only half of the SH2s).

		Coolgame		Nov 25, 2011
			antime said: You'll gain the best insight of the SCU DSP's capabilities by reading the SCU manual and the tutorial tech note (SOA-8). Its main strength is performing series of single-cycle multiplications, and if you can't keep the multiplier busy the work is probably better performed on one of the main CPUs (the SCU DSP instruction set is awkward for more general-purpose programming, and the clock frequency is only half of the SH2s). i read those soa tutorial notes and the SCU manual on the dsp, even the (SBL) basic library manual. but can you tell me about how to use the dsp in light calculation? does it do gourad shading? I think i can make a supreb engine if i can program the dsp to do lighting (gourad shading) and pre clipping while the other processors do their thang. can it do pre clipping? p.s i know im off topic to orginally talk about the b-bus, im sorry, do you think i should start a new message board subject?

		rorirub		Nov 29, 2011
			Gourad Shading is applied by the VDP1, but lightning should be handled by your software code.