implemented MERGE command

c64/basic/basic_commands_CC/cmd_bload_bverify.s

@@ -0,0 +1,41 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+
+cmd_bverify:
+
+	// LOAD and VERIFY are very similar, from BASIC perspective there is almost no difference;
+	// just different parameter passed to Kernal and different error message in case of failure
+
+	lda #$01                           // mark operation as VERIFY
+	skip_2_bytes_trash_nvz
+
+cmd_bload:
+
+	lda #$00                           // mark operation as LOAD
+	sta VERCKB
+
+	// Set default device and secondary address; channel is not important now
+
+	jsr select_device
+	ldy #$00                           // secondary address 0 - it has to be loaded precisely where we want
+	jsr JSETFLS
+
+	// Fetch the file name
+
+	jsr fetch_filename
+	bcc !+
+
+	// No filename supplied - this should only be allowed for tape (device number below 8)
+
+	lda FA
+	and #%11111000
+	bne_16 do_MISSING_FILENAME_error
+
+	lda #$00
+	sta FNLEN
+!:
+	// XXX finish the implementation
+
+	jmp do_NOT_IMPLEMENTED_error