Re: VGA emulation in BOCHS

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


------------------------------------------------------------------------------
Everyone hates slow websites. So do we.
Make your web apps faster with AppDynamics
Download AppDynamics Lite for free today:
http://p.sf.net/sfu/appdyn_sfd2d_oct