PDA

View Full Version : sh5, memory ampliation,...



bender
September 19th, 2004, 12:25
well, i've been speaking with some friends and they have toold me that the sh5 it's 100% pin compatible with the sh4 and supports 100% the sh4
also about memory, there have been some interesting memory upgrades for the gp32 replacing the ram chips. I think it should be possible to replace those chips for the dreamcast for similar ones that have more capacity(the chips could perhaps be found in some pcs dimms ;)

What do you think guys? has anyone tried to do those mods? i think ithe dreamcast scene needs something similar, will solve the optimization problems with the ports and we still would have the compatibility with the commercial games
any site i have missed?
thnks :)

quzar
September 19th, 2004, 17:36
well, i've been speaking with some friends and they have toold me *that the sh5 it's 100% pin compatible with the sh4 and supports 100% the sh4

thats just not true. It is not pin compatible at all, only instruction set compatible.

I know because over a year ago i asked a representative of SuperH the same question:



I can answer your question, which is quite complex and involves both
CPU
architecture and specific device information.

1. The SH-4 is a 32-bit CPU with an instruction set branded as
SHcompact. The SH-5 is a 64-bit CPU that supports the SHcompact
instruction set and adds a new multimedia instruction set called
SHmedia.

This means that binaries written for SH-4 would run on SH-5. However in
the Dreamcast there are many peripherals and system components and
changing CPU is not really a practical option unless you have access to
the all the source code written by Sega. You could contact Sega but I
doubt they will give out this material.

2. Pin compatibility
The Sega Dreamcast was built with the SH-4 CPU and a set of peripherals
e.g. memory interface, UART etc. The actual device was manufactured by
Hitachi Semiconductor (now called Renesas Technology, see
www.renesas.com) but it is not for sale any more.

There is no version of the SH-5 that is pin compatible with the SH-4
device used in the Dreamcast so it is not possible to swap out the
chips.

Sorry that we do not have any better solution for you.
Best regards
Mark Jones
Business Development

bender
September 19th, 2004, 18:48
very good answer.
thnks 8)

interesting site with the gp32 ram upgrade, pics inside
http://www.cobbleware.com/gp32/gp32ram.html
i've been thinking in emailing this guy asking about his opinion about the dreamcast and a ram mod, but my english really sucks and i don't really know what i should ask. if anyone thinks this is interesting, please do it ;)

Alexvrb
September 19th, 2004, 19:40
thats just not true. It is not pin compatible at all, only instruction set compatible.
That's not what he said quzar. He said it wasn't pin compatible with the SH4 in the Dreamcast. In other words, it probably IS pin compatible with typical SH4s. Also, it runs all the standard SH4 instructions, but does a standard SH5 have the extra instructions in the DC's variant?

quzar
September 19th, 2004, 22:09
That's not what he said quzar. He said it wasn't pin compatible with the SH4 in the Dreamcast. In other words, it probably IS pin compatible with typical SH4s. Also, it runs all the standard SH4 instructions, but does a standard SH5 have the extra instructions in the DC's variant?

Since he was talking about the dreamcast, when he said Sh-4 i assumed he meant the SH7750(?) that was in the Dreamcast, not another SH-4 chip. About the backwards compatibility, I'm not sure =P.

bender
September 20th, 2004, 16:46
about the ram mod i think it should be possible. The sh4 should be able to address more than those 16mb. ;)

Kamjin
September 20th, 2004, 20:54
The memory is more than likely possible, but the work involved.. ehhh..
In reality there hasn't been a real need for more memory, if it's a question of large carts for emulators, then it would be easier to build an interface for them off the expansion bus.
I think the way to go is to still examine the overclocking, speed is for the emu's is still a higher priority..

Alexvrb
September 20th, 2004, 23:10
Since he was talking about the dreamcast, when he said Sh-4 i assumed he meant the SH7750(?) that was in the Dreamcast, not another SH-4 chip. About the backwards compatibility, I'm not sure =P.What I want to know is more info on the SH4A chips they're working on. Not as powerful as the SH5s, but they may well have more in common with the older chips. Damnit, someone should build a DC-compatible box and throw one of those in there, it wouldn't be an expensive addition. Use it as part of the sound subsystem in the Xbox 2 or something. Like the Genesis did :P, it has a SMS compatibility mode.

bender
September 21st, 2004, 08:50
The memory is more than likely possible, but the work involved.. ehhh..
In reality there hasn't been a real need for more memory, if it's a question of large carts for emulators, then it would be easier to build an interface for them off the expansion bus.
I think the way to go is to still examine the overclocking, speed is for the emu's is still a higher priority..

i was thinking in putting a lot of Mb and trying to run naomi games using a dc, lol ;D
if your overclocking thing gets into an stable point, without corrupting the vmu files, more ram could perhaps help for some arcade emus, neogeo (cartridge system) or an n64 one(i'm just dreaming ;) ). I think, there are also some linux games that can't be ported due to the lack of some Mb

bender
September 29th, 2004, 12:55
Speaking about the sh5 with a guy, he says that there could be between 2 and 4 different versions of this micro. He tells me that one of those was 100% pin compatible and supported 100% the sh4 instruction set, last time he looked at. Perhaps this compatible sh5 it's not being sold anymore and the reason because quzar got that answer
I don't have a link to post so i can't verify this, though ::)

Alexvrb
September 29th, 2004, 16:03
No, you misunderstand. I thought I already straightened this up. There IS a version of the SH5 that is pin and instruction compatible with at least one major SH4 package. That is a true statement. However, I yet again reiterate the fact that the SH4 in the Dreamcast is not just a standard SH7750 chip. It is custom. So therefore just because the SH5 in question is pin compatible with some kind of SH4 and instruction compatible with the "SH4 instruction set" doesn't automatically mean it is fully compatible with the DC's SH4. It may not support the extra instructions. Not to mention that the pin design/layout could be custom too. So it's not suitable for upgrading the DC, even if you could overcome any other problems.

I would like to mention (I think I said it in the DC2 thread) that if you were building a completely new system, you could emulate the DC's SH4 on the SH5. So you could make a new inexpensive console that is backwards compatible. Unfortunetely that's yet another crazy pipe dream.

Rufus
September 29th, 2004, 22:22
Just for curiousity sake, could you provide a link which describes the differences between a standard SH7750 and the customized version used in the DC?

quzar
September 29th, 2004, 23:00
Also, even if there are SH5s that are pin-compatible, they still are not compatible with the prehipherals the DC uses (internal ones). ALSO just because there are SH5s that are pin compatible with A SH4 doesnt mean there are ones pin compatible with the sh4 used in teh DC.

Alexvrb
September 29th, 2004, 23:51
Just for curiousity sake, could you provide a link which describes the differences between a standard SH7750 and the customized version used in the DC?
You mean do I feel like digging up some Sega documents or whatever, that I probably shouldn't have access to anyway even if I found them? No, not particularly. BlackAura and others would know more about it anyway.

quzar
September 30th, 2004, 05:33
I think the only person who would know what ops are in the SH4 DC as opposed to the SH4 standard is Rand.

bender
September 30th, 2004, 09:56
I see it now, Alexvrb, quzar :) . Thnks for the explanation. I haven't read that the dc's sh4 it's different (my english sometimes really sucks :-[ ) So the only possible thing to have really a powerfull and compatible system it's to try to build a new system with some kind of motherboard that already supports the sh5 and adding all the needed peripheals and emulate the whole dreamcast. Seems very expensive and a hard task, though :-/

elefas
October 5th, 2004, 14:55
By reading the official sega documents on dreamcast hardware outline, in the system specifications section I came across the following:

? 16MB Main memory(Can expand to a maximum of 32MB)
? 8MBTexture memory(Can expand to a maximum of 16MB)
? 2MB Boot ROM
? 128KB Flash memory
? 2MB audio memory(Can expand to a maximum of 8MB)

The parenthesis show that the memory installed on DC can be expanded, otherwise why should they mention it? There are also some diagrams, I am not a hardware expert but what I understood is that it uses 2 64Mbit (4 x 512k x 32bit) blocks of RAM connected to the SH4 cpu. The problem is that SH4 cpu has 12 address pins available for memory addressing and 64bit data bus in which half pins are connected to the 1st module of RAM and the other half to the second module. So if I am right, we cant connect lets say another 2 same RAM modules (not enough space for the data bus) but the 12bit address bus can support memory modules twice as big as the default ones. In conclusion we may expand the dc main memory by replacing the default modules with others of twice capacity, the address lines can support it. However I don't know how we could "inform" the dreamcast to use this extra space (I suppose it needs bios upgrade).

Ohh, the above are just some simple thoughts. An experienced hardware guy probably will get more by reading the documentation.

Alexvrb
October 5th, 2004, 15:49
Yes, memory expansion is more feasible than replacing the processor. I've been told that you wouldn't even need to modify the BIOS, although I've been told the opposite as well. Maybe someone will do it eventually, but unfortunetely any sort of complicated internal modification would never see widespread use. The only way you could get a large portion of people to upgrade would be through an external expansion, and I don't see anything like that happening either.