Hi
As possible do protected mode?
Why? For raising system reliability.
Processor Must have 2 modes system and user. Bit "super"
In the field of memories is conducted place which is only read in mode
"user".
If processor causes function of system that super=on. Access To registers of
governing protection of memory possible in this mode only.
Preceding mode returns When leaving
That this for registers?
For example:
Mapper Mask Register MMR[7..0] Kernel will be able to select necessary
amount of pages for MSX & DOS2
MMR[].d=d[7..0];
MMR[].clk=/IOWR;
MMR[].ena=(A[7..0]== { adres of MMR } );
MMR[].reset=reset;
IF super THEN
mask[7..0]=B"00000000"
ELSE
mask[7..0]=MMR[7..0].q
END IF;
Cycle write to mapper
Mapper[7..0]=d[7..0] and not(mask[7..0]);
Cycle read to mapper
d[7..0]=Mapper[7..0] or mask[7..0];
Example two: Kernel can protect upper area memories by permit 16 kb ( pseudo
ROM )
MemoryProtectRegister MPR[7..0]
LoMem=(A[23..16]==0)
IF LoMem THEN
IMA[21..14]=mapper[7..0]; -- IMA is internel adress
ELSE
IMA[21..14]=A[21..14];
END IF;
mem_protect=( IMA[21..14]=> MPR[7..0].q) and not(super);
Example3: Protect invalid -opcode vector
mem_protect=(A[23..2]==0) & not(super)
If think possible to do anything else. Main that this was not complex. Be
also possibility to lengthen mapper before 16 bits of command Z80 will be
able to change only younger byte, Z380 both using OUTW
But that will say you ? :)
Valery
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