more work towards tape error correction

c64/kernal/tape/tape_normal_get_data_2.s

@@ -0,0 +1,51 @@
+// #LAYOUT# STD *        #TAKE
+// #LAYOUT# *   KERNAL_0 #TAKE
+// #LAYOUT# *   *        #IGNORE
+
+//
+// Tape (normal) helper routine - data block (backup) reading
+//
+
+
+#if CONFIG_TAPE_NORMAL
+
+
+tape_normal_get_data_2:
+
+	// First check if there is a need to read anything
+
+	lda PTR1
+	beq tape_normal_get_data_2_checksum
+
+	// Read sync of the block
+	
+	ldy #$09
+	jsr tape_normal_sync
+	bcs tape_normal_get_data_2_done    // Carry already set, will indicate error
+	jsr tape_normal_get_marker
+
+	// FALLTROUGH
+
+tape_normal_get_data_2_loop:
+
+	// XXX read missing bytes
+
+	sec
+	rts
+
+
+tape_normal_get_data_2_checksum:
+
+	// Validate checksum
+
+	lda RIPRTY
+	cmp #$01                           // sets Carry if checksum verification fails
+
+	// FALLTROUGH
+
+tape_normal_get_data_2_done:
+
+	rts
+
+
+#endif