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Fixed #662 (3E+ initialization description)

This commit is contained in:
thrust26 2020-06-11 16:20:10 +02:00
parent 298eea04cf
commit 7584558746
1 changed files with 5 additions and 13 deletions
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18
src/emucore/Cart3EPlus.hxx
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@ -42,7 +42,7 @@ class System;
ROM: ROM:
Note: in descriptions $F000 is equivalent to $1000 -- that is, we only deal Note: In descriptions $F000 is equivalent to $1000 -- that is, we only deal
with the low 13 bits of addressing. Stella code uses $1000, I'm used to $F000 with the low 13 bits of addressing. Stella code uses $1000, I'm used to $F000
So, mask with top bits clear :) when reading this document. So, mask with top bits clear :) when reading this document.
@ -51,16 +51,10 @@ class System;
The last 1K ROM ($FC00-$FFFF) segment in the 6502 address space (ie: $1C00-$1FFF) The last 1K ROM ($FC00-$FFFF) segment in the 6502 address space (ie: $1C00-$1FFF)
is initialised to point to the FIRST 1K of the ROM image, so the reset vectors is initialised to point to the FIRST 1K of the ROM image, so the reset vectors
must be placed at the end of the first 1K in the ROM image. Note, this is must be placed at the end of the first 1K in the ROM image.
DIFFERENT to 3E which switches in the UPPER bank and this bank is fixed. This
allows variable sized ROM without having to detect size. First bank (0) in ROM is
the default fixed bank mapped to $FC00.
The system requires the reset vectors to be valid on a reset, so either the Note: This is DIFFERENT to 3E which switches in the UPPER bank and this bank is
hardware first switches in the first bank, or the programmer must ensure fixed. This allows variable sized ROM without having to detect size.
that the reset vector is present in ALL ROM banks which might be switched
into the last bank area. Currently the latter (programmer onus) is required,
but it would be nice for the cartridge hardware to auto-switch on reset.
ROM switching (write of block+bank number to $3F) D7D6 upper 2 bits of bank # ROM switching (write of block+bank number to $3F) D7D6 upper 2 bits of bank #
indicates the destination segment (0-3, corresponding to $F000, $F400, $F800, indicates the destination segment (0-3, corresponding to $F000, $F400, $F800,
@ -100,11 +94,9 @@ class Cartridge3EPlus: public Cartridge3E
@param size The size of the ROM image @param size The size of the ROM image
@param md5 The md5sum of the ROM image @param md5 The md5sum of the ROM image
@param settings A reference to the various settings (read-only) @param settings A reference to the various settings (read-only)
@param bsSize The size specified by the bankswitching scheme
(where 0 means variable-sized ROM)
*/ */
Cartridge3EPlus(const ByteBuffer& image, size_t size, const string& md5, Cartridge3EPlus(const ByteBuffer& image, size_t size, const string& md5,
const Settings& settings, size_t bsSize = 0); const Settings& settings);
virtual ~Cartridge3EPlus() = default; virtual ~Cartridge3EPlus() = default;
public: public: