Nov 152017
 

A couple of years ago, RISC OS Open Ltd started building versions of RISC OS with “zero page relocation” – with the memory map changed such that the kernel’s workspace that started at the bottom of the addressable memory was moved to a higher location. This was an important step for security and stability, and for the future of the operating system.

However, it wasn’t ever going to happen without some casualties along the way; software that in some way tried to use or access certain information held in that workspace and which therefore found it no longer available. Aemulor, the 26-bit emulator that allows applications that are not yet fully 32-bit run on newer hardware, was one such casualty – and an important one at that. Continue reading »

 November 15, 2017  Posted by  Software Tagged with: , , , ,
Sep 082012
 

Make your 32-bit computer do an Impression (ho-ho) of a 26-bit one!

When Castle Technology Ltd launched the IYONIX pc, back in 2002, there was a significant question users needed an answer to before upgrading to the new computer: Would their old software run on the new hardware?

The problem was that for all the previous RISC OS computers, the ARM CPUs worked in (or supported in the case of StrongARM) an addressing mode we refer to as ’26-bit’, in which the program counter and processor status flags are contained in a single register; six bits are used for the status flags, and 26 bits for the program counter – the pointer to where in memory instructions are read for execution. With instructions always being word-aligned, rather than byte-aligned, the 26-bit program counter actually provides a 28-bit address range, representing bits 2 to 27 in the actual address – the lower two bits pointing to the instruction to be read are always zero. Continue reading »