Re: VGA emulation in BOCHS

I am now running BOCHS emulated CPUs in parallel ( i.e. on separate
host os threads). only the  BX_CPU(0) is decrementing the
countDownEvent. However, i get an assertion in libx11.so shared
library when i run many CPUs ( i.e. 8 CPUs). i suspect it is due to
the fact that the libx11 is not thread safe and more than 1 CPUs are
working in the x.cc code.   If only BX_CPU(0)  is decrementing the
countDownEvent. can other thread also have access to anything in the
GUI ?


Thank you,
Xin


On Thu, Oct 18, 2012 at 3:42 PM, Volker Ruppert
<[email protected]> wrote:
> Hi!
>
>
>> I am looking at how BOCHS emulates VGA. it seems to be that VGA memory
>> is within a fixed memory range and different processors can write to
>> the memory using PIO or MMIO.  when the countDownEvent is called. The
>> current states in the VGA buffer is updated to the X window through
>> xcblib APIs. I have 2 questions.
>> 1. what sets up the fixed memory region for VGA ? The BIOS ?
>
>
> The VGA memory regions are defined in the PC standard and the VGA init code
> registers the memory handlers for it. That's all in the ISA case and with no
> extension enabled. In the PCI case and with Bochs VBE or Cirrus extension
> the PCI BIOS initializes the bases address regions for RAM and ROM. In this
> case these PC standard compatible regions are also present:
>
> A0000 - AFFFF  EGA/VGA graphics window
> B0000 - B7FFF  Monochrome text mode
> B8000 - BFFFF  CGA graphics and color text mode
> C0000          Start address of the VGA BIOS ROM
>
>
>> 2. Is the update to x windows only invoked from the vga update
>> function which is called by countDownEvent ?
>
>
> The display adapter code registers a virtual timer und the timer function
> executes the update code for the display library (gui). In earlier versions
> of Bochs there was a parameter 'vga_update_interval' and a standard timer
> (in pc_system.cc) was initialized with it's value.
> Now we are using the bochsrc option 'vga: update_freq' to set up the screen
> update timing and the timer value is calculated internally. In addition to
> this we are using a virtual timer that calls the screen updates with
> realtime frequency if the option 'clock: sync=realtime' is used. I'd like to
> use always realtime for the VGA screen updates, but I haven't managed to
> rewrite the virtual timer code yet.
>
> --
> Volker
>

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