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more doc updates for atari5200

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Christian Groessler 2014-05-27 02:44:59 +02:00
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doc/atari5200.sgml
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@ -5,7 +5,7 @@
<title>Atari 5200 specific information for cc65
<author>
<url url="mailto:chris@groessler.org" name="Christian Groessler"><newline>
<date>2014-05-15
<date>2014-05-27
<abstract>
An overview over the Atari 5200 runtime system as it is implemented for the
@ -39,18 +39,29 @@ config.
<sect>Memory layout<p>
cc65 generated programs with the default setup run with the I/O area and a
CHR bank enabled, which gives a usable memory range of &dollar;8000 - &dollar;FFF3.
All boot ROM entry points may be called directly without additional code.
cc65 generated programs with the default setup use the RAM space from &dollar;021C to
&dollar;3FFF. If you want to reserve memory for the display list and screen buffer
you should define the __RESERVED_MEMORY__ linker variable. The number
of bytes specified by __RESERVED_MEMORY__ are lowering the top of
memory, therefore the available
RAM memory for the program is &dollar;021C to &dollar;3FFF-__RESERVED_MEMORY__.
The default linker config file sets __RESERVED_MEMORY__ to &dollar;1E0
to reserve space for an optional CONIO text screen.
Special locations:
<descrip>
<tag/Text screen/
The text screen is located at VRAM &dollar;2000.
The text screen is only enabled if any of the CONIO output routines
is used in the program. Its size is 20x24 characters (Antic mode 6,
BASIC mode 1). The text screen is located at &dollar;3E00. The
address of the screen memory is available at runtime in the variable
SAVMSC (&dollar;001B).<p>
If the program doesn't use any CONIO output functions it needs to setup its own
display list.
<tag/Stack/
The C runtime stack is located at &dollar;7FFF and growing downwards.
The C runtime stack is located at &dollar;3FFF-__RESERVED_MEMORY__ and growing downwards.
<tag/Heap/
The C heap is located at the end of the program and grows towards the C
@ -68,31 +79,43 @@ Programs containing Atari 5200 specific code may use the <tt/atari5200.h/ header
<sect1>Atari 5200 specific functions<p>
<itemize>
<item>???
<item>TBD.
</itemize>
<sect1>Hardware access<p>
The following pseudo variables declared in the <tt/nes.inc/ include file do
allow access to hardware located in the address space.
The following pseudo variables declared in the <tt/atari5200.h/ header
file do allow access to hardware located in the address space. Some
variables are structures, accessing the struct fields will access the
chip registers.
<descrip>
<tag><tt/PPU/</tag>
The <tt/PPU/ defines allow access to the PPU chip.
<tag><tt/GTIA_READ/ and <tt/GTIA_WRITE/</tag>
The <tt/GTIA_READ/ structure allows read access to the GTIA. The
<tt/GTIA_WRITE/ structure allows write access to the GTIA.
See the <tt/_gtia.h/ header file located in the include directory
for the declaration of the structure.
<tag><tt/APU/</tag>
The <tt/APU/ defines allow access to the APU chip.
<tag><tt/POKEY_READ/ and <tt/POKEY_WRITE/</tag>
The <tt/POKEY_READ/ structure allows read access to the POKEY. The
<tt/POKEY_WRITE/ structure allows write access to the POKEY.
See the <tt/_pokey.h/ header file located in the include directory
for the declaration of the structure.
<tag><tt/ANTIC/</tag>
The <tt/ANTIC/ structure allows read access to the ANTIC.
See the <tt/_antic.h/ header file located in the include directory
for the declaration of the structure.
</descrip><p>
<sect>Loadable drivers<p>
All drivers must be statically linked because no file I/O is available.
All drivers must be statically linked because no disk I/O is available.
The names in the parentheses denote the symbols to be used for static linking of the drivers.
@ -135,11 +158,8 @@ No serial drivers are available for the Atari 5200.
<sect1>Disk I/O<p>
The existing library for the Atari 5200 doesn't implement C file
I/O. There are no hacks for the <tt/read()/ and <tt/write()/ routines.
To be more concrete, this limitation means that you cannot use any of the
following functions (and a few others):
Disk I/O is not supported by the <tt/atari5200/ target. This means that
you cannot use any of the following functions (and a few others):
<itemize>
<item>fclose