<title>Atari specific information for cc65
<author>Shawn Jefferson, <htmlurl
url="mailto:shawnjefferson@24fightingchickens.com"
-name="shawnjefferson@24fightingchickens.com"> and
+name="shawnjefferson@24fightingchickens.com"> and
Christian Groessler, <htmlurl url="mailto:cpg@aladdin.de" name="cpg@aladdin.de">
-<date>14-Sep-2004
+<date>03-Jan-2006
<abstract>
An overview over the Atari runtime system as it is implemented for the cc65 C
<tag/Stack/
The C runtime stack is located at MEMTOP and grows downwards,
regardless of how your linker config file is setup. This
- accomodates the different memory configurations of the Atari
+ accommodates the different memory configurations of the Atari
machines, as well as having a cartridge installed. You can override
this behaviour by writing your own crt0.s file and linking it to
your program (see also <ref name="Final note"
<sect1>Graphics drivers<p>
Currently there are no graphics drivers available for the Atari platform.
+However, the runtime library provides a function named _graphics, with
+a mode parameter just like the BASIC GRAPHICS command. This function will
+switch to the requested graphics mode.
+There are currently no functions available to access the graphics
+memory. The access must be implemented manually.
+
+Many graphics modes require more memory than the text screen which is
+in effect when the program starts up. Therefore the programmer has to
+tell the program beforehand the memory requirements of the graphics
+modes the program intends to use.
+This can be done by using the __RESERVED_MEMORY__ linker config
+variable. The number specified there describes the number of bytes to
+subtract from the top of available memory as seen from the runtime
+library. This memory is then used by the screen buffer.
+
+The numbers for the different graphics modes presented below should
+only be seen as a rule of thumb. Since the screen buffer memory needs
+to start at specific boundaries, the numbers depend on the current top
+of available memory.
+The following numbers were determined by a BASIC program.
+
+<table>
+<tabular ca="rr">
+graphics mode|reserved memory@<hline>
+0|1@
+1|1@
+2|1@
+3|1@
+4|1@
+5|182@
+6|1182@
+7|3198@
+8|7120@
+9|7146@
+10|7146@
+11|7146@
+12|162@
+13|1@
+14|3278@
+15|7120@
+16|1@
+17|1@
+18|1@
+19|1@
+20|1@
+21|184@
+22|1192@
+23|3208@
+24|7146@
+25|7146@
+26|7146@
+27|7146@
+28|160@
+29|1@
+30|3304@
+31|7146
+</tabular>
+<caption>reserved memory required for different graphics modes
+</table>
+
+The values of "1" are needed because the graphics command crashes if
+it doesn't have at least one byte available. This seems to be a bug of
+the Atari ROM code.
<sect1>Extended memory drivers<p>
<descrip>
- <tag><tt/atari-stdjoy.joy/</tag>
+ <tag><tt/ataristd.joy/</tag>
Supports up to four standard joysticks connected to the joystick ports of
the Atari.
+ <tag><tt/atarim8.joy/</tag>
+ Supports up to eight standard joysticks connected to a MultiJoy adapter.
+
</descrip><p>
<sect>Limitations<p>
+<sect>DIO implementation<label id="dio"><p>
+
+The Atari supports disk drives with either 128 or 256 byte sectors.
+The first three sectors of any disk are always 128 bytes long though. This is
+because the system can only boot from 128 bytes sectors.
+
+Therefore the DIO read and write functions transfer only 128 bytes
+for sectors 1 to 3, regardless of the type of diskette.
+
+
+<sect>CONIO implementation<label id="conio"><p>
+
+The console I/O is speed optimized therefore support for XEP80 hardware
+or f80.com software is missing. Of course you may use stdio.h functions.
+
<sect>Other hints<p>
These are defined to be Atari + number key.
-<sect1>Reserving a memory area inside
the program<label id="memhole"><p>
+<sect1>Reserving a memory area inside
a program<label id="memhole"><p>
The Atari 130XE maps its additional memory into CPU memory in 16K
chunks at address $4000 to $7FFF. One might want to
the program should go below $4000 and the DATA and RODATA
segments should go above $7FFF.
<p>
-The main problem is that the EXE header generated by the cc65 runtine
+The main problem is that the EXE header generated by the cc65 runtime
lib is wrong. It defines a single load chunk with the sizes/addresses
-of the CODE, RODATA, and DATA segments (the whole user program).
+of the LOWCODE, INIT, CODE, RODATA, and DATA segments (the whole user
+program).
<p>
The contents of the EXE header come from the EXEHDR segment, which is
-defined in crt0.s. This cannot be changed w/o modifiying and
+defined in crt0.s. This cannot be changed w/o modifying and
recompiling the cc65 atari runtime lib. Therefore the original EXE
header must be discarded. It will be replaced by a user created
one.
<p>
The user needs to create a customized linker config file which adds
-new memory areas and segments to hold the new EXE header and added
-load chunk header data. Also an assembly source file needs to be
-created which defines the contents of the new EXE header and the
-second load chunk header.
+new memory areas and segments to hold the new EXE header and the
+header data for the second load chunk. Also an assembly source file
+needs to be created which defines the contents of the new EXE header
+and the second load chunk header.
<p>
<p>
This is a modified cc65 Atari linker configuration file (split.cfg):
SECHDR: start = $0000, size = $4, file = %O; # second load chunk
RAM: start = $8000, size = $3C20, file = %O; # $3C20: matches upper bound $BC1F
+ TRAILER: start = $0000, size = $0006, file = %O;
}
SEGMENTS {
- EXEHDR: load = BANK, type = wprot;
+ EXEHDR: load = BANK, type = ro;
- NEXEHDR: load = HEADER, type = wprot; # first load chunk
- CODE: load = RAMLO, type = wprot, define = yes;
+ NEXEHDR: load = HEADER, type = ro; # first load chunk
+ LOWCODE: load = RAMLO, type = ro, define = yes, optional = yes;
+ INIT: load = RAMLO, type = ro, optional = yes;
+ CODE: load = RAMLO, type = ro, define = yes;
- CHKHDR: load = SECHDR, type = wprot; # second load chunk
- RODATA: load = RAM, type = wprot, define = yes;
+ CHKHDR: load = SECHDR, type = ro; # second load chunk
+ RODATA: load = RAM, type = ro, define = yes;
DATA: load = RAM, type = rw, define = yes;
BSS: load = RAM, type = bss, define = yes;
ZEROPAGE: load = ZP, type = zp;
- AUTOSTRT: load = RAM, type = wprot; # defines program entry point
+ AUTOSTRT: load = TRAILER, type = ro; # defines program entry point
}
FEATURES {
CONDES: segment = RODATA,
}
SYMBOLS {
__STACKSIZE__ = $800; # 2K stack
+ __RESERVED_MEMORY__: value = $0, weak = yes;
}
</verb></tscreen>
<p>
The contents of the new NEXEHDR and CHKHDR segments come from this
file (split.s):
<tscreen><verb>
- .import __CODE_LOAD__, __BSS_LOAD__, __CODE_SIZE__
- .import __DATA_LOAD__, __RODATA_LOAD__
+ .import __LOWCODE_LOAD__, __BSS_LOAD__, __CODE_SIZE__
+ .import __CODE_LOAD__, __DATA_LOAD__, __RODATA_LOAD__
.segment "NEXEHDR"
.word $FFFF ; EXE file magic number
; 1st load chunk
- .word __CODE_LOAD__
+ .word __LOWCODE_LOAD__
.word __CODE_LOAD__ + __CODE_SIZE__ - 1
.segment "CHKHDR"
<sect2>Low data and high code example<p>
-Goal: Put RODATA and DATA into low memory and CODE with BSS into high
-memory (split2.cfg):
+Goal: Put RODATA and DATA into low memory and LOWCODE, INIT, CODE, BSS
+into high memory (split2.cfg):
<tscreen><verb>
MEMORY {
SECHDR: start = $0000, size = $4, file = %O; # second load chunk
RAM: start = $8000, size = $3C20, file = %O; # $3C20: matches upper bound $BC1F
+ TRAILER: start = $0000, size = $0006, file = %O;
}
SEGMENTS {
- EXEHDR: load = BANK, type = wprot; # discarded old EXE header
+ EXEHDR: load = BANK, type = ro; # discarded old EXE header
- NEXEHDR: load = HEADER, type = wprot; # first load chunk
- RODATA: load = RAMLO, type = wprot, define = yes;
+ NEXEHDR: load = HEADER, type = ro; # first load chunk
+ RODATA: load = RAMLO, type = ro, define = yes;
DATA: load = RAMLO, type = rw, define = yes;
- CHKHDR: load = SECHDR, type = wprot; # second load chunk
- CODE: load = RAM, type = wprot, define = yes;
+ CHKHDR: load = SECHDR, type = ro; # second load chunk
+ LOWCODE: load = RAM, type = ro, define = yes, optional = yes;
+ INIT: load = RAM, type = ro, optional = yes;
+ CODE: load = RAM, type = ro, define = yes;
BSS: load = RAM, type = bss, define = yes;
ZEROPAGE: load = ZP, type = zp;
- AUTOSTRT: load = RAM, type = wprot; # defines program entry point
+ AUTOSTRT: load = TRAILER, type = ro; # defines program entry point
}
FEATURES {
CONDES: segment = RODATA,
}
SYMBOLS {
__STACKSIZE__ = $800; # 2K stack
+ __RESERVED_MEMORY__: value = $0, weak = yes;
}
</verb></tscreen>
New contents for NEXEHDR and CHKHDR are needed (split2.s):
<tscreen><verb>
- .import __CODE_LOAD__, __BSS_LOAD__, __DATA_SIZE__
+ .import __LOWCODE_LOAD__, __BSS_LOAD__, __DATA_SIZE__
.import __DATA_LOAD__, __RODATA_LOAD__
.segment "NEXEHDR"
.word __DATA_LOAD__ + __DATA_SIZE__ - 1
.segment "CHKHDR"
- .word __CODE_LOAD__
+ .word __LOWCODE_LOAD__
.word __BSS_LOAD__ - 1
</verb></tscreen>
projects / cc65 / blobdiff