Re: Give MDA/VGA a try.

[Matan Ziv-Av <ma...@sv...>]

On Sat, 8 Jul 2000, James Simmons wrote:

> > The mdacon driver detects a mda card only by checking if memory at
> > 0xb0000 is accessible (for write and read). If your vga card does decode
> > those addressess, I can think of the following options:
> > * enable the commented out tests in mda_detect.
> 
> Short term solution.

It might be a good solution. It seems to me that test_mda_b is wrong. It
does not restore the register value to what it was, which might be the
reason. Try replacing the function with 

static int test_mda_b(unsigned char val, unsigned char reg)
{
        unsigned long flags;
        unsigned char save;

        save_flags(flags); cli();

        outb_p(reg, mda_index_port);
        udelay(20);
        save=inb_p(mda_value_port);
        udelay(20);
        outb  (val, mda_value_port);

        udelay(20); val = (inb_p(mda_value_port) == val);

        udelay(20);
        outb_p(save,mda_value_port);

        restore_flags(flags);

        return val;
}

This works on my mda without the reported cursor problems. Please check
if it indeed Does not recognise your vga card.

> > * make the mda driver disable all pci vga cards, before probing for mda.
> > * don't insmod mdacon.c on a system without a mda driver.
> > * find a better way to detect an mda card.
> 
> Long term solution. Just have to find info on MDA. Anyone know where docs
> are for MDA ?

Actually, I am not sure that there is such a test. the 6845 is very
simple, and if a vga card emulates it it might emulate it completely.

From PC Intern and vgadoc4b:

port 0x3b8 Control:
bit 0 - must be 1
bit 3 - enable screen
bit 5 - bit 7 of attribute is 0-bold 1-blinking

port 0x3ba Status (RO):
bit 0 - Horiz sync 
bit 3 - pixel status (current pixel sent to monitor)
All other bits are 1.

port 0x3b4, 0x3b5 CRTC:
index
0	Horizontal Total Register (-1)
1	Horizontal Displayed Register (-1)
2	Horizontal Sync Position Register
3	Horizontal Sync Width Register
4	Vertical Total Register
5	Vertical Total Adjust Register
6	Vertical Displayed Register
7	Vertical SyncPosition Register
8	Interlace Mode Register
9	Maximum Scan Line Register (-1)
a	Cursor Start Register (bits 0-4 cursor start,
	bits 5-6 cursor attributes)
b	Cursor End Register
c	Start Address High Register
d	Start Address Low Register
e	Cursor Location High Register
f	Cursor Location Low Register


-- 
Matan Ziv-Av.                         ma...@sv...