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Commit Graph

5 Commits

Author SHA1 Message Date
Marshall Ward
09495519c0 NES memory map amend (16k prg, 8k chr default)
The configuration file and runtime (crt0.s) provided for the default NES
ROM layout (2x16k PRG, 8k CHR) incorrectly added interrupts (IRQ1, IRQ2,
TIMERIRQ) which are not supported by the NES hardware.  For example, see
the NESdev wiki, which makes no reference to these interrupts.

    https://wiki.nesdev.com/w/index.php/CPU_memory_map

The VECTORS region was also incorrectly set to 0xFFF6, which would have
left the 0xFFF4 normally unspecified.  This did not result in any error,
however, since cc65 simply placed ROMV directly after ROM0 regardless of
start address.

(This layout may be due to a copy-and-paste from the PC-Engine
configuration, whose interrupt registers start at 0xFFF6, begins with
the three interrupts listed above, followed by NMI and START, and does
not end with a final IRQ interrupt.)

Despite the absence of any actual error, since START is still placed at
0xFFFC, this patch removes the nonexistent interrupts and also correctly
aligns the ROM0 and ROMV regions.  It also has the (admittedly very
minor) benefit of freeing up 6 additional bytes for ROM0.
2016-12-24 08:32:54 +11:00
Oliver Schmidt
d5092d2d3f Consider the segment attributes 'define' and 'optional' mutually exclusive.
In normal situations it isn't too useful to define symbols for optional segments as those symbols can't be presumed to be always present.

I in fact suspect that most currently present combinations of 'define' and 'optional' aren't useful - apart form the overlay configurations of course.
2016-03-17 21:31:43 +01:00
Oliver Schmidt
0edd05b4bf Removed symbol definition for ONCE.
Almost all targets don't need symbols for the ONCE segment. Likely their definition was a C&P error in the first place.
2016-03-15 22:55:34 +01:00
Oliver Schmidt
419eb700b5 Renamed INITBSS to INIT and INIT to ONCE.
The way we want to use the INITBSS segment - and especially the fact that it won't have the type bss on all ROM based targets - means that the name INITBSS is misleading. After all INIT is the best name from my perspective as it serves several purposes and therefore needs a rather generic name.

Unfortunately this means that the current INIT segment needs to be renamed too. Looking for a short (ideally 4 letter) name I came up with ONCE as it contains all code (and data) accessed only once during initialization.
2016-03-06 21:27:19 +01:00
Oliver Schmidt
37c492b544 Replaced builtin linker configs with ordinary .cfg files.
The benefits are:
- Independency of ld65 build from perl
- More transparent behaviour
2013-04-09 23:09:46 +02:00