Re: [MiNT] VBR not part of context switch?

[Markus Fröschle <markus@mubf.de>]

On Coldfire microcontrollers, the VBR register is write only. You'd need an error-prone shadow variable to make it part of the context switch.

Would have been a nice feature for virtualization, probably (a term that wasn't common at the time the Coldfire instruction set was designed), but designers obviously decided that system control registers (accessed by movec instruction) are for system control features _only_.

Am 22.07.2013 um 19:28 schrieb Vincent Rivière:

> On 22/07/2013 17:07, Peter Persson wrote:
>> How come the VBR isn't part of the context switch?
> 
> I guess that only user stuff is concerned by context switch.
> A program manipulating supervisor stuff is probably not multitask friendly.
> 
> About sr, I guess that if it is fully saved among context switches, that's a side effect. I would bet that the original intent was only to save the CCR status bits, not IPL stuff, etc.
> 
> But of course, FreeMiNT is Free Software, so we are free to hack it for our own needs :-)
> 
> -- 
> Vincent Rivière
> 
>