From dc38b7d950d71425c89eff81799de26724798d2a Mon Sep 17 00:00:00 2001
From: OBattler <oubattler@gmail.com>
Date: Mon, 1 Aug 2022 03:16:44 +0200
Subject: [PATCH] The PIC now correctly processes slave interrupts in XT mode
 as well, fixes PS/2 mouse on the Xi8088, fixes #2045.

---
 src/pic.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/src/pic.c b/src/pic.c
index 857f45cfc..12fd80264 100644
--- a/src/pic.c
+++ b/src/pic.c
@@ -724,10 +724,25 @@ pic_irq_ack(void)
 {
     int ret;
 
+    /* Needed for Xi8088. */
+    if ((pic.ack_bytes == 0) && pic.int_pending && pic_slave_on(&pic, pic.interrupt)) {
+	if (!pic.slaves[pic.interrupt]->int_pending) {
+		/* If we are on AT, IRQ 2 is pending, and we cannot find a pending IRQ on PIC 2, fatal out. */
+		fatal("IRQ %i pending on AT without a pending IRQ on PIC %i (normal)\n", pic.interrupt, pic.interrupt);
+		exit(-1);
+		return -1;
+	}
+
+	pic.interrupt |= 0x40;		/* Mark slave pending. */
+    }
+
     ret = pic_irq_ack_read(&pic, pic.ack_bytes);
     pic.ack_bytes = (pic.ack_bytes + 1) % (pic_i86_mode(&pic) ? 2 : 3);
 
     if (pic.ack_bytes == 0) {
+	/* Needed for Xi8088. */
+	if (pic.interrupt & 0x40)
+		pic2.interrupt = 0x17;
 	pic.interrupt = 0x17;
 	update_pending();
     }