From 0f4cb443b4d34dfceef35c0f9b31abcf69d00c67 Mon Sep 17 00:00:00 2001 From: Oliver Schmidt Date: Sat, 19 Dec 2020 19:54:12 +0100 Subject: [PATCH] Improved device I/O under DOS 3.3 Certain scenarios (e.g. not running any Applesoft program at all since booting DOS 3.3) can make DOS 3.3 consider cc65 device input (e.g. getchar()) that reads a CR interpreting the command in the keyboard buffer. Setting the hibyte of the Applesoft currently executed line number to some value <> $FF (beside setting the input prompt to some value <> ']') makes DOS 3.3 understand that we're not in intermediate mode and that therefore I/O not preceded with ctrl-d mustn't be fiddled with (see DOS 3.3 routine at $A65E). --- asminc/apple2.inc | 1 + libsrc/apple2/read.s | 9 ++++++--- 2 files changed, 7 insertions(+), 3 deletions(-) diff --git a/asminc/apple2.inc b/asminc/apple2.inc index 5ebf73164..528c463a1 100644 --- a/asminc/apple2.inc +++ b/asminc/apple2.inc @@ -15,6 +15,7 @@ PROMPT := $33 ; Used by GETLN RNDL := $4E ; Random counter low RNDH := $4F ; Random counter high HIMEM := $73 ; Highest available memory address+1 +CURLIN := $75 ; Current line number being executed ;----------------------------------------------------------------------------- ; Vectors diff --git a/libsrc/apple2/read.s b/libsrc/apple2/read.s index 14c80b7e2..99c189cbd 100644 --- a/libsrc/apple2/read.s +++ b/libsrc/apple2/read.s @@ -19,11 +19,14 @@ .segment "ONCE" initprompt: - ; Set prompt <> ']' to let DOS 3.3 know that we're - ; not in Applesoft immediate mode and thus keep it - ; from scanning our device I/O for DOS commands. + ; Set prompt <> ']' and currently executed Applesoft + ; line number hibyte <> $FF to let DOS 3.3 (at $A65E) + ; know that we're not in Applesoft immediate mode and + ; thus keep it from scanning our device I/O for DOS + ; commands. lda #$80 ; Same value used at $D52C sta PROMPT + sta CURLIN+1 ; Any value <> $FF will do rts .code