small startup/interrupt cleanup

c64/kernal/interrupts/hw_entry_reset.s

@@ -0,0 +1,44 @@
+// Resources describing the C64 reset sequence:
+// https://www.c64-wiki.com/wiki/Reset_(Process)
+
+
+hw_entry_reset:
+
+	// The GPL program at https://github.com/Klaus2m5/6502_65C02_functional_tests/blob/master/6502_functional_test.a65
+	// uses the following initial reset sequence, affirmed by c64 PRG p269
+#if !HAS_BCD_SAFE_RESET
+	cld // for CPUs having undefined D flag after reset
+#endif
+	ldx #$FF
+	txs
+	sei
+
+	// The following routine is based on reading the public KERNAL jumptable routine
+	// list, and making unimaginative assumptions about what should be done on reset.
+	// Also, https://codebase64.org/doku.php?id=base:assembling_your_own_cart_rom_image was used
+	// as it shows example startup sequence, to be followe by cartridge creators
+
+	// C64 PRG p269
+	jsr cartridge_check
+	bne !+
+	jmp (ICART_COLD_START)
+!:
+	// Initialising IO is obviously required. Also indicated by c64 prg p269.
+	jsr JIOINIT
+	
+	// Setting up the screen and testing ram is obviously required
+	// also affirmed by p269 of c64 prg
+	jsr JRAMTAS // called RANTAM on Codebase64 wiki
+	
+	// Resetting IO vectors is obviously required, if we want interrupts to run
+	// also affirmed by c64 prg p269
+	jsr JRESTOR
+
+	//  "Compute's Mapping the 64" p236
+	jsr JCINT
+
+	// What do we do when finished?  A C64 jumps into the BASIC ROM
+	cli // allow interrupts to happen
+
+	// c64 prg p269
+	jmp (IBASIC_COLD_START)