Reverse engineering the 6522 VIA chip?

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dreamseal
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Reverse engineering the 6522 VIA chip?

Post by dreamseal » Wed Mar 28, 2018 9:07 pm

I have some experience (on a hobby basis) in reverse engineering the logic of NMOS silicon die shots. I was wondering if anyone would be interested if I were to make a start on reversing the logic of the 6522 VIA chip from the images on the following web pages:

http://visual6502.org/images/pages/MOS_6522.html

http://siliconpr0n.org/map/mos/6522/dlyr1_mit20x/

The second link is of an image with the metal layer removed, so it shows only the diffusion, polysilicon, and contacts.

Something similar has already been done with the 6502 (see the home page of visual6502.org if you're not familiar with it).

If people are interested, then what I would do is start a new topic in an appropriate section (not sure which section to put it in at this stage) and I would add a post for each small section that I reverse, with an image of that section of the die shot with the layers traced around in different colours for the different materials, and also a logic diagram of the reversed logic for the small section of the die shot shown. John D McMaster made a start on tracing around the layers, but he has since abandoned the effort. I asked him about this and he said he likes to focus on producing die shots rather than doing the reversing itself. He says there are far more people prepared to reverse the logic once a die shot is produced than there are people able to decap and image a silicon chip.

The MOS 6522 VIA chip was used in a number of 8-bit machines, so such a forum topic and series of posts would be of interest to a forum devoted to any of those machines, but due to my new found love of the Oric, I would like to create them here, if people think that the defence-force forums is an appropriate place for it.

If the consensus is yes, then I will add that to my list of Oric-related projects (which seems to be growing each week at the moment). What section would be best to create such a topic in? I was thinking of the "Technical questions" section, but technically its not a question (although perhaps I'd be posing a question of "what's inside the 6522?" and then would set about trying to answer that question). If not the "Technical questions" section, then maybe General is the next best. It is quite a technical and hardware related topic though.

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NekoNoNiaow
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Re: Reverse engineering the 6522 VIA chip?

Post by NekoNoNiaow » Thu Mar 29, 2018 5:56 am

My, that would be quite an undertaking, I hope you are assisted with good vision analysis software during this task. ;)

Do not take my opinion as representative of the community in any way (I only infrequently dabble in Oric stuff) but although I find the idea of reverse engineering the 6522 chip fascinating, from an Oric perspective it would make more sense to decap/photograph the chip responsible for video production (I forgot its designation) since this could allow to exploit it in yet unforeseen very practical ways.

For example, if its address generator could be manipulated this would potentially pave the way for double buffering techniques in HIRES mode (one can dream!). ;)

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dreamseal
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Re: Reverse engineering the 6522 VIA chip?

Post by dreamseal » Thu Mar 29, 2018 6:41 am

I quite agree, but unfortunately there isn't yet a die shot of the HCS10017 that I know of. Decaping and imaging isn't something I'm able to do myself. I would quite happily switch to the HCS10017 when a die shot does become available.

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Dbug
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Re: Reverse engineering the 6522 VIA chip?

Post by Dbug » Thu Mar 29, 2018 6:53 am

dreamseal wrote:
Wed Mar 28, 2018 9:07 pm
What section would be best to create such a topic in? I was thinking of the "Technical questions" section, but technically its not a question (although perhaps I'd be posing a question of "what's inside the 6522?" and then would set about trying to answer that question). If not the "Technical questions" section, then maybe General is the next best. It is quite a technical and hardware related topic though.
As long as it is in the Oric Hardware subsection of the forum, it does not really matter.
"Technical questions" can also be thought as "Technical Answers To Questions You Did not Even Know You Were Wondering About" :)

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