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Omega PCI docs exist By Chris Williams. Published: 24th Nov 2004, 15:47:01 | Permalink | PrintableBut who wants them?  We can confirm that documentation covering the Omega PCI system, is available.
The techy bits
The PCI documentation is actually a good read and basically describes MicroDigital's PCI API: it all appears to make sense, SWIs are listed with entry and exit parameters and other details like DMA are discussed. Whoever wrote it has their head screwed on, and it's worlds apart from the statements previously released on MD's website.
The Omega PCI system is controlled by the PCIManager module, which manages the PCI bus and devices connected to it. It allows drivers to control individual devices, read information from them and configure interrupts.
The Omega motherboard also features a number of PCI devices in its Southbridge chip: UDMA IDE, two USB 1.1 controllers and a bridge to a another I/O chip that provides the floppy drive, serial and parallel ports and a PS/2 interfaces.
The politics
MicroDigital's API is very similar to Castle's PCI API, which is understandable as both APIs cater for the same industry standard PCI interface - but the APIs are not exactly the same.
They both share some of the same SWI names. For example, PCI_ReadID on an Iyonix and an Omega both read the vendor and ID information from a PCI card, but the entry and exit registers are defined differently. The Castle API has SWIs that the Omega API doesn't have, and vice-versa. Also, the way in which interrupts and memory mapping are handled differ between APIs. Finally, the MD API SWI base is 0x50E40 and the Castle base is 0x50380.
This isn't the first time we've seen an API split in the land of RISC OS. There's also the API divide between the Castle USB API and the Simtec USB API, which can't be helpful for potential developers, nor users who are torn over which USB card to buy, as each card has a different range of drivers.
It's a mild headache for developers who want to support PCI cards for both Iyonix and Omega users - but then, we can only think of one third party who's actively developing PCI stuff, and that's Simon Wilson. While his PCITV software for Iyonix users has been a success, he's been approached by only two users for an Omega port.
Until we were forwarded a copy of the documents earlier this month, we were a little concerned about whether or not such information existed. Once you've developed, released and marketed a new computer, you ideally want third party software developers to write drivers for your kit. Users will find your product more attractive if they can buy your machine and plug in all sorts of new stuff. It makes financial sense to therefore entice developers by offering lots of detailed and comprehendible guides and documents on how to write software for your hardware. So we're relieved to see that this information describing how to get code talking to the Omega's PCI hardware exists. Everyone wins.
Of course, the API text file originally came from an Omega owner and later passed onto us, and we didn't download or otherwise receive the text directly from MicroDigital. Castle earned themselves brownie points from the userbase by publishing their documentation online (the quality of the documentation is another matter, it's the thought that counts for some), while companies including RISCOS Ltd. are chastised for keeping their documentation for paying customers only. In ROL's case, they had a number of people working on the documentation at one point, which was eventually released to Select subscribers. Although the development team was in favour of publically releasing the docs, management had other ideas.
You never know: perhaps if MicroDigital were to publically release their hardware documentation, it could help boost the popularity of their kit.
Links
MicroDigital website
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