Fixed cbm_k_readst() to work around a VIC-20 Kernal bug.

It properly returns the RS-232 device's status.
2021-01-13 03:20:19 -05:00
parent 0f1386ff4c
commit 710c6c6f2f
3 changed files with 37 additions and 8 deletions
--- a/libsrc/vic20/c_readst.s
+++ b/libsrc/vic20/c_readst.s
@@ -0,0 +1,28 @@
+;
+; 1999-06-03, Ullrich von Bassewitz
+; 2021-01-12, Greg King
+;
+; unsigned char cbm_k_readst (void);
+;
+; This version works around a bug in VIC-20 Kernal's READST function.
+;
+
+        .include        "vic20.inc"
+        .include        "../cbm/cbm.inc"
+
+        .export         _cbm_k_readst
+
+
+_cbm_k_readst:
+        ldx     #>$0000
+        lda     DEVNUM
+        cmp     #CBMDEV_RS232
+        beq     @L1
+
+        jmp     READST
+
+; Work-around:  Read the RS-232 status variable directly.
+
+@L1:    lda     RSSTAT
+        stx     RSSTAT          ; reset the status bits
+        rts