From 3fd78208bab5cd7d8fa601a4a94af3f66ed39ec1 Mon Sep 17 00:00:00 2001
From: Colin Leroy-Mira <colin@colino.net>
Date: Mon, 19 Feb 2024 18:27:34 +0100
Subject: [PATCH] Disable IRQ if opening at 115200 bps

---
 doc/apple2.sgml            |  5 +++++
 doc/apple2enh.sgml         |  5 +++++
 libsrc/apple2/ser/a2.ssc.s | 10 ++++++++--
 3 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/doc/apple2.sgml b/doc/apple2.sgml
index e6ec870ee..99ff8139e 100644
--- a/doc/apple2.sgml
+++ b/doc/apple2.sgml
@@ -452,10 +452,15 @@ The names in the parentheses denote the symbols to be used for static linking of
   (RTS/CTS) and does interrupt driven receives. Speeds faster than 9600 baud
   aren't reachable because the ROM and ProDOS IRQ handlers are too slow.
   Software flow control (XON/XOFF) is not supported.
+
   Note that because of the peculiarities of the 6551 chip transmits are not
   interrupt driven, and the transceiver blocks if the receiver asserts
   flow control because of a full buffer.
 
+  Note that using the driver at SER_BAUD_115200 will disable IRQs. It will be up
+  to the users to use the serial port, either by re-enabling IRQs themselves,
+  or by directly poll-reading the ACIA DATA register without the help of ser_get().
+
   The driver defaults to slot 2. Call <tt/ser_apple2_slot()/ prior to
   <tt/ser_open()/ in order to select a different slot. <tt/ser_apple2_slot()/
   succeeds for all Apple&nbsp;II slots, but <tt/ser_open()/ fails with
diff --git a/doc/apple2enh.sgml b/doc/apple2enh.sgml
index d47820cc7..9c46bd4fb 100644
--- a/doc/apple2enh.sgml
+++ b/doc/apple2enh.sgml
@@ -453,10 +453,15 @@ The names in the parentheses denote the symbols to be used for static linking of
   (RTS/CTS) and does interrupt driven receives. Speeds faster than 9600 baud
   aren't reachable because the ROM and ProDOS IRQ handlers are too slow.
   Software flow control (XON/XOFF) is not supported.
+
   Note that because of the peculiarities of the 6551 chip transmits are not
   interrupt driven, and the transceiver blocks if the receiver asserts
   flow control because of a full buffer.
 
+  Note that using the driver at SER_BAUD_115200 will disable IRQs. It will be up
+  to the users to use the serial port, either by re-enabling IRQs themselves,
+  or by directly poll-reading the ACIA DATA register without the help of ser_get().
+
   The driver defaults to slot 2. Call <tt/ser_apple2_slot()/ prior to
   <tt/ser_open()/ in order to select a different slot. <tt/ser_apple2_slot()/
   succeeds for all Apple&nbsp;II slots, but <tt/ser_open()/ fails with
diff --git a/libsrc/apple2/ser/a2.ssc.s b/libsrc/apple2/ser/a2.ssc.s
index 7053b7bb1..88dc4572c 100644
--- a/libsrc/apple2/ser/a2.ssc.s
+++ b/libsrc/apple2/ser/a2.ssc.s
@@ -302,6 +302,7 @@ HandshakeOK:
         lda     (ptr1),y        ; Baudrate index
         tay
         lda     BaudTable,y     ; Get 6551 value
+        sta     tmp2            ; Backup for IRQ setting
         bpl     BaudOK          ; Check that baudrate is supported
 
         lda     #SER_ERR_BAUD_UNAVAIL
@@ -332,8 +333,13 @@ BaudOK: sta     tmp1
 
         ora     #%00000001      ; Set DTR active
         sta     RtsOff          ; Store value to easily handle flow control later
-        ora     #%00001000      ; Enable receive interrupts (RTS low)
-        sta     ACIA_CMD,x
+
+        ora     #%00001010      ; Disable interrupts and set RTS low
+
+        ldy     tmp2            ; Don't enable IRQs if 115200bps
+        beq     :+
+        and     #%11111101      ; Enable receive IRQs
+:       sta     ACIA_CMD,x
 
         ; Done
         stx     Index           ; Mark port as open