How to port RISC OS 5 to the RiscPCPublished: 30th Jan 2007, 01:16:49 | Permalink | Printable
Possible but not a top priority for RISC OS OpenThe RISC OS Open team have revealed the technical ins and outs of producing a RiscPC build of RISC OS 5 as well as uncovering the development history of the operating system. Ever since the launch of the ROOL scheme, there has been a high level of interest in a RiscPC port, and a lengthy document was published over the weekend outlining the work required to produce such a version of RISC OS 5.
The briefing also deflates conspiracy theories lurking around the whispered topic of how the OS was developed post-1998, and how the different Pace, RISCOS Ltd and Castle strands of RISC OS came about.
Ex-Pace engineer Ben Avison, who authored the document on the ROOL website, said the RiscPC-compatible source code for RISC OS 3.6 still exists in the vaults - however after that, things get slightly complicated. The OS kernel is split into three streams, the 'trunk', the 'Ursula' branch, and the HAL branch. Any of them can be used for a RiscPC port, but each has its own pros and cons. Ursula split from the main-line trunk after the release of RISC OS 3.71, in order to form an OS for the doomed Pheobe project, and was later used to seed RISCOS Ltd's stream of RISC OS.
When Acorn's yellow bombshell was canned, parts of Ursula were merged back into the trunk, and the option to run the OS in 32bit mode was later added. This become the Pace "homebrew RISC OS 4". The trunk then split again, according to Ben, forming the HAL branch - in which chipset support was moved out of the kernel, more optimisations from Ursula were brought in, and development was taken over by Tematic.
A hardware abstraction layer for the Acorn IOMD and VIDC chipset, as found in RiscPC-class machines, appears to exist, and it makes use of undocumentated aspects of the RISC OS 5 HAL system.
In his essay, Ben noted: "There still seems to be plenty of interest in building shared-source RISC OS for the Risc PC, but there is much confusion about what would be involved in doing so.
"First, understand that this is not top priority for ROOL - ROOL's policy is that it's more important to focus on releasing all the components needed to do an Iyonix ROM and disc build first.
"Only after this will the remaining components be vetted for release, although those components that relate to RiscPC hardware support are probably good candidates to be the next on the list."
See the link below for more information.
Building RISC OS 5 for the RiscPC
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