even more startup tweaks
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@@ -56,18 +56,16 @@ cint_pal:
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!:
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sta TVSFLG
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// Setup KEYLOG vector - XXX is it proper place?
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cint_brk: // entry for BRK and STOP+RESTORE - XXX, where should it start?
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// Setup KEYLOG vector
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lda #<scnkey_set_keytab
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sta KEYLOG+0
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lda #>scnkey_set_keytab
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sta KEYLOG+1
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cint_brk: // entry for BRK and STOP+RESTORE - XXX, where should it start?
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jsr setup_vicii
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// Initialise cursor blink flags (Compute's Mapping the 64 p215)
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// Initialise cursor blink flags (Compute's Mapping the 64 p215)
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lda #$01
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sta BLNCT
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@@ -93,15 +91,18 @@ cint_brk: // entry for BRK and STOP+RESTORE - XXX, where should it start?
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dex
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bpl !-
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sta BufferQuantity
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#endif
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// Set key repeat delay (Compute's Mapping the 64 p215)
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// Making some numbers up here: Repeat every ~1/10th sec
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// But require key to be held for ~1/3sec before
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// repeating (Compute's Mapping the 64 p58)
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// Not needed for default keyboard scanning code
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ldx #22-2 // Fudge factor to match speed
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stx DELAY
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#endif
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// Set current colour for text (Compute's Mapping the 64 p215)
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ldx #$01 // default is light blue ($0E), but we use a different one
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@@ -115,5 +116,9 @@ cint_brk: // entry for BRK and STOP+RESTORE - XXX, where should it start?
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ldx #$00
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stx MODE
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// Setup video and I/O
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jsr setup_vicii
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// Fallthrough/jump to screen clear routine (Compute's Mapping the 64 p215)
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jmp clear_screen
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@@ -8,8 +8,6 @@
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setup_vicii:
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// XXX it should also set default devices
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// Clear everything - turn off sprites (observed hanging around after
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// running programs and resetting), etc.
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@@ -0,0 +1,49 @@
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// Resources describing the C64 reset sequence:
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// https://www.c64-wiki.com/wiki/Reset_(Process)
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hw_entry_reset:
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// The GPL program at https://github.com/Klaus2m5/6502_65C02_functional_tests/blob/master/6502_functional_test.a65
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// uses the similar initial reset sequence, affirmed by c64 PRG p269
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sei // disable the interrupts, as fast as possible - they are disabled in case of HW reset,
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// but this routine can be also called manually
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ldx #$00
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sta VIC_SCROLX // turn the display off - we want as little screen artifacts as possible
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cld // required for all CPUs - due to possibility of manual call
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dex // $FF - to initialize stack pointer
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txs
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// The following routine is based on reading the public KERNAL jumptable routine
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// list, and making unimaginative assumptions about what should be done on reset.
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// Also, https://codebase64.org/doku.php?id=base:assembling_your_own_cart_rom_image was used
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// as it shows example startup sequence, to be followe by cartridge creators
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// C64 PRG p269
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jsr cartridge_check
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bne !+
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jmp (ICART_COLD_START)
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!:
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// Initialising IO is obviously required. Also indicated by c64 prg p269.
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jsr JIOINIT
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// Setting up the screen and testing ram is obviously required
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// also affirmed by p269 of c64 prg
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jsr JRAMTAS // called RANTAM on Codebase64 wiki
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// Resetting IO vectors is obviously required, if we want interrupts to run
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// also affirmed by c64 prg p269
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jsr JRESTOR
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// "Compute's Mapping the 64" p236
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jsr JCINT
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// What do we do when finished? A C64 jumps into the BASIC ROM
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cli // allow interrupts to happen
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// c64 prg p269
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jmp (IBASIC_COLD_START)
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@@ -0,0 +1,5 @@
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System reset routine has to be placed under it's original location due to 'SYS 64738' being extremaly popular to reset the C64,
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to the point it went into popular culture.
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https://twitter.com/hashtag/SYS64738?src=hash
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https://www.computerhope.com/jargon/s/sys64738.htm
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@@ -13,7 +13,7 @@ IOINIT:
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// Set $00/$01 port mode and value
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// We want BASIC and KERNAL ROMs mapped, and datasette motor off
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// (https://www.c64-wiki.com/wiki/Zeropage)
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// XXX - Work around VICE bug: Writing $00 before $01 results in rubbish in $01
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// Work around for VICE bug: Writing $00 before $01 results in rubbish in $01
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// after. https://sourceforge.net/p/vice-emu/bugs/1057/
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lda #$27
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ldx #$2F
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@@ -0,0 +1,91 @@
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//
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// Official Kernal routine, described in:
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//
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// - [RG64] C64 Programmer's Reference Guide - page 291
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// - [CM64] Compute's Mapping the Commodore 64 - page 237
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//
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// CPU registers that has to be preserved (see [RG64]): none
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//
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ramtas_real:
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// C64 Programmer's Reference guide p291:
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// Clear $0000-$0101, $0200-$03ff
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// PGS: $0000, $0001 are CPU IO ports, so shouldn't get written to
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ldy #$02
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lda #$00
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!:
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sta $00,y
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iny
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bne !-
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!:
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// How many ways are there to efficiently erase these two pages
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// of RAM? We would like to avoid any unnecessary byte similarity
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// with the C64 KERNAL. Thus we do $0300 before $0200, even though
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// with the longer sequence of identicale bytes we see no basis for
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// it being copyrightable. Again, we just want to redue the attack
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// surface for any misguided suit.
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sta $0300,Y
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sta $0200,Y
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iny
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bne !-
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// Allocate cassette buffer
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// "Mapping the C64", p237
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lda #<$033C
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sta TAPE1+0
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lda #>$033C
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sta TAPE1+1
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// set screen address to $0400
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// https://www.c64-wiki.com/wiki/Screen_RAM
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// Since we are setting $D018, we also make sure we are using the
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// ROM character set (C64 Programmer's Reference Guide p322)
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lda #$14
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sta VIC_YMCSB
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// Make sure we have the correct VIC-II memory bank for the screen to really be at $0400
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// and not $4400, $8400 or $C400
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// https://www.c64-wiki.com/wiki/VIC_bank#Selecting_VIC_banks
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lda CIA2_DDRA
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ora #$03
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sta CIA2_DDRA
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lda CIA2_PRA
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ora #$03
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sta CIA2_PRA
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// Set screen address pointer ("Compute's Mapping the 64" p238)
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// This is obvious boiler plate containing no creative input, but to avoid
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// unnecessarily similarity to the C64 KERNAL, we use X instead of A to do this,
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// and several following
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ldx #>$0400
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stx HIBASE
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// Work out RAM size and put in MEMSTR and MEMSIZK
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// "Compute's Mapping the 64", p54
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// http://unusedino.de/ec64/technical/project64/mapping_c64.html
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ldx #>$0800
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stx MEMSTR+1
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ldx #$00
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stx MEMSTR+0
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stx MEMSIZK+0
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// Try to modify $8000, if it fails then RAM ends at $7FFF, else $9FFF
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ldx $8000
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inx
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stx $8000
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cpx $8000
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bne ramtas_32K_RAM
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dex
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stx $8000
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ldx #$A0
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stx MEMSIZK+1
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bne !+ // always non-zero, saves one byte
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ramtas_32K_RAM:
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dex
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stx $8000 // case there is RAM under the ROM
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ldx #$80
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stx MEMSIZK+1
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!:
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rts
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