Re: A85: FIND_PIXEL
[Prev][Next][Index][Thread]
Re: A85: FIND_PIXEL
JUSTIN BOSCH wrote:
>
> -> Nope. I should explain how the TI's Rom works. The ROM is 128k, but
> -> 16 bit addressing would only allow 64k to be accessed! So the 64k is
> -> divided into 32k RAM, 16k ROM, and 16K paged ROM. The ROM is divided
> -> into 8 pages: page 0 holds the important functions (all ROM_CALLS
> -> except FIND_PIXEL). So the first 16k of ROM is page 0, and it is
> -> always present! by changing to page 4 you change the 2nd 16K of ROM.
> -> Of course, since FIND_PIXEL is the only ROM_CALL NOT on page 0, you
> -> do not need to change it back, until you exit the shell. But the
> -> shell does it automatically! So you really don't have to do anything.
> -> TI-ROM experts, correct me if I am wrong.
>
> If I want to use any of the other functions I STILL don't have to change
> it back? Sorry to bother everyone but this is confusing.
I though I had replied to this earlier, but I never got it back.. Maybe
it never got sent.. Anyways:
Page 0 does _NOT_ hold all the important functions, it just holds a
table of their addresses towards the end of the page. When the Shells
jump the a ROM function, they actually jump to this table, which calls a
routine in page 0 to change the ROM page, then jump the the routine,
after which another routine in ROM changes the page back, then returns
to the original location. MOST if not all of the ROM routines used by
ZShell/CShell/WhateverShell are on pages other than page 0, but all of
them except FIND_PIXEL have an entry on the table at the end of page 0.
In answer to your question: No, you _DON'T_ have to change the ROM page
back after using FIND_PIXEL.
--
* * * * * * * * * * * * * * *
* Wolfgang Amadeus Mozart *
* <mozart@technologist.com> *
* * * * * * * * * * * * * * *
Follow-Ups:
References: