From b239edfbe11fda4c5a3ca388dd5eeb350b7b0258 Mon Sep 17 00:00:00 2001
From: Andreas Baumann <mail@andreasbaumann.cc>
Date: Sat, 30 Jan 2021 19:27:18 +0100
Subject: improved debug mode (d) for toggling

---
 LINKS            |  8 ++++++++
 doc/MINIMAL.6502 | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 emu/6522.h       |  1 +
 emu/emul.c       | 19 +++++++++++++++++++
 4 files changed, 77 insertions(+)
 create mode 100644 doc/MINIMAL.6502

diff --git a/LINKS b/LINKS
index 7f1a915..e312378 100644
--- a/LINKS
+++ b/LINKS
@@ -120,6 +120,10 @@ https://github.com/davepoo/6502Emulator
 https://github.com/spacerace/6502
 https://www.masswerk.at/products.php
 
+other minimal PC projects
+https://github.com/slu4coder/Minimalistic-8-Bit-CPU
+https://www.youtube.com/channel/UCXYQcMpUBT3aaQKfmAVJNow
+
 other emulators:
 https://github.com/pdewacht/oberon-risc-emu (RISC-5 Wirth Emulator, as inspiration)
 
@@ -149,3 +153,7 @@ https://github.com/vndmtrx/check-cmake-example
 
 cmake:
 https://samthursfield.wordpress.com/2015/11/21/cmake-dependencies-between-targets-and-files-and-custom-commands/
+
+languages for 6502:
+https://dwheeler.com/6502/
+http://cowlark.com/cowgol/
diff --git a/doc/MINIMAL.6502 b/doc/MINIMAL.6502
new file mode 100644
index 0000000..ae2044d
--- /dev/null
+++ b/doc/MINIMAL.6502
@@ -0,0 +1,49 @@
+Immediate ADI
+Absolute  ADA
+Relative  ADR
+
+little endian
+
+lda
+sta
+clr
+neg
+inc
+dec
+cpi
+adc
+sbc
+jmp
+jsr
+
+nop
+clc
+sec
+not
+lsl
+rol
+lsr
+ror
+asr
+rts
+phs
+pls
+
+
+rel
+word at abs adr
+SP+rel
+
+bran
+
+no interrups, but win/out
+
+0x7fff 255 byte stack (instead of 0x100 to 0x1ff on 6502)
+
+sts/lds store relative to stack
+function calls with parameters
+
+XXW codes, acting on 16-bit words
+
+WIN, OUT as shortcurs, not really necessary
+relative addressing for jumps would help to write relocatable code by hand
diff --git a/emu/6522.h b/emu/6522.h
index d3bade7..27e191c 100644
--- a/emu/6522.h
+++ b/emu/6522.h
@@ -38,6 +38,7 @@ typedef struct via_6522_t
 	uint8_t ddrb;
 	uint8_t pcr;
 	uint8_t ier;
+	uint8_t ifr;
 
 	bool debug;
 	
diff --git a/emu/emul.c b/emu/emul.c
index 21ab58b..7086737 100644
--- a/emu/emul.c
+++ b/emu/emul.c
@@ -81,6 +81,7 @@ static void print_help( void )
 		"(f) fini (continue to next rts)\n"
 		"(c) for continue running\n"
 		"(b) break to single stepping\n"
+		"(d) toggle debug output\n"
 		"(+) speed up\n"
 		"(-) speed down\n"
 		"(p) push the button\n"
@@ -124,6 +125,19 @@ void emul_run( emul_t *emul, int nof_steps )
 						case SDLK_s:
 							cpu_6502_run_steps( emul->cpu, 1 );
 							break;
+						case SDLK_d:
+							if( emul->speed < 250 ) {
+								emul->debug = !emul->debug;
+								fprintf( stderr, "debug mode is %s\n", ( emul->debug) ? "on" : "off" );
+								if( emul->debug ) {
+									emul->cpu->debug_flags |= DEBUG_STATUS;
+								} else {
+									emul->cpu->debug_flags &= ~DEBUG_STATUS;
+								}
+							} else {
+								fprintf( stderr, "enabling debug mode now not possible, CPU is too fast!\n" );
+							}
+							break;
 						case SDLK_EQUALS:
 						case SDLK_KP_EQUALS:
 						case SDLK_PLUS:
@@ -133,6 +147,11 @@ void emul_run( emul_t *emul, int nof_steps )
 								emul->speed = CPU_FREQUENCY;
 							}
 							fprintf( stderr, "CPU speed  is %1.6f MHz now\n", ( (double)emul->speed / 1000000 ) );
+							if( emul->speed > 250 ) {
+								emul->debug = false;
+								emul->cpu->debug_flags &= ~DEBUG_STATUS;;
+								fprintf( stderr, "disabling debug mode because the CPU is too fast now!\n" );
+							}
 							break;
 						case SDLK_MINUS:
 						case SDLK_KP_MINUS:
-- 
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