[A86] Re: TCP/IP stack

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[A86] Re: TCP/IP stack



On Mon, 24 Sep 2001 12:43:41 +0000 "David West" <bdaddy_mit@hotmail.com>
writes:
> >The built-in memory system does this already, why not use it?
> >Then you could have a small program to boot your shiny OS from 
> TI-OS in
> >case of a bad crash.
> 
> Two comments:
> (1)   How could the "built-in" memory system solve the problem of 
> user 
> process space fragmentation due to the loading and unload of program 
> images 
> into runnable z80 address space.  As I understand it, the "built-in" 
> memory 
> system saves data variables acrossed a paged memory map.  Are you 
> saying 
> that one of these variables could be a program?  You wouldn't be 
> able to 
> directly execute it cause it would not always be located in 
> executable ram.  
> Elaborate on how the "built-in" memory system could be used to 
> manage 
> multiple program images (while they are being executed)?

If you use  a relocatable program format (either using only relative
addresses, patching all absolute addresses, or having the program itself
calculate them), you can execute programs of up to 16k directly in place
by loading 2 consecutive ram pages to the two swappable banks.  This does
make ROM calls a little tricky, since the call table can't be loaded at
the same time: 
  ld hl,VariableName-1
  rst 20h ; copy name to OP1
  rst 10h ; get the abs addr
  ld a,b
  ex de,hl
  call _load_ram_ahl
  in a,(6)
  out (5),a
  ; **** You cannot make
  ; ROM calls starting here
  inc a
  out (6),a
  set 6,h ; switch hl from
  res 7,h ; bank 2 to bank 1
  ; execute program
  ld a,$0d
  out (5),a
  ; **** ROM calls are safe

If programs are interpreted/emulated then they're just like basic
programs and there's no problem.

> (2)   When the new OS is booted, it takes over everything.  >
Potentially > wiping out all previous knowledge of the other OS.  As a
result, > when it is > running, there is no TI-OS VAT or other
datastructures to fall back > on.  If > the new OS crashes, the only
thing to fall back on is a reboot back > into a > clean TI-OS.> > > 

If you don't wipe out the VAT, you can use Kirk Meyer's memory recovery
tool  (I can never remember the names of his stuff...), then start the
new OS again.  Actually, as long as you keep the important stuff in the
middle of ram, you can restart the new os even without that.

-josh
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