implemented BASIC command OLD

doc/Extended-BASIC.md

@@ -13,6 +13,10 @@ Tries to switch the machine to turbo mode - details differ depending on the conf
 
 Tries to switch the machine back to 1 MHz operation mode.
 
+### `OLD`
+
+Tries to restore program destroyed by NEW or a reset.
+
 ### `MERGE "file_name" [, device_number]`
 
 Appends the BASIC program from a storage medium to the one currently present in memory.

src/basic/basic_commands_CC/cmd__jumptable_CC.s

@@ -13,7 +13,9 @@
 
 	cmd_bload,
 	cmd_bsave,
-	cmd_bverify
+	cmd_bverify,
+
+	cmd_old
 )
 
 

src/basic/basic_commands_CC/cmd_old.s

@@ -0,0 +1,64 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+
+cmd_old:
+
+	// First make sure we are in direct mode
+
+	ldx CURLIN+1
+	inx
+	bne_16 do_DIRECT_MODE_ONLY_error
+
+	// Now try to restore program linkage
+
+	ldy #$01
+	tya
+	sta (TXTTAB),y
+
+	jsr LINKPRG
+
+	// Now we have to restore VARTAB    XXX deduplicate this with line editor
+
+	lda TXTTAB+0
+	sta OLDTXT+0
+	lda TXTTAB+1
+	sta OLDTXT+1
+!:
+	lda OLDTXT+0
+	sta VARTAB+0
+	lda OLDTXT+1
+	sta VARTAB+1
+
+	jsr basic_follow_link_to_next_line
+
+	lda OLDTXT+0
+	ora OLDTXT+1
+	bne !-                                       // branch if pointer not NULL
+
+	// Correct VARTAB by 2 bytes NULL pointer
+
+#if HAS_OPCODES_65CE02
+
+	inw VARTAB
+	inw VARTAB
+
+#else
+
+	clc
+	lda VARTAB+0
+	adc #$02
+	sta VARTAB+0
+	bcc !+
+	inc VARTAB+1
+!:
+#endif
+
+	// Call CLR to restore remaining variables
+
+	jsr do_clr
+
+	// Quit
+
+	jmp shell_main_loop

tools/generate_strings.cc

@@ -181,6 +181,7 @@ const StringEntryList GLOBAL_Keywords_CC =  { ListType::KEYWORDS, "keywords_CC",
 	{ true,  true,  true,  "KCC_02",   "BLOAD",        }, // http://www.antonis.de/qbebooks/gwbasman/bload.html
 	{ true,  true,  true,  "KCC_03",   "BSAVE",        }, // http://www.antonis.de/qbebooks/gwbasman/bsave.html
 	{ true,  true,  true,  "KCC_04",   "BVERIFY",      },
+	{ true,  true,  true,  "KCC_05",   "OLD",          }, // OpenROMs specific, not present in CBM BASIC dialects
 } };
 
 // extended BASIC keywords - reserved for BASIC commands likely making sense on most C64-compatible machines