From 5fd9ee39091086d107c533c33c86db2c62bc96be Mon Sep 17 00:00:00 2001
From: Seth Morabito <web@loomcom.com>
Date: Tue, 10 Aug 2021 19:29:41 -0700
Subject: [PATCH] 3B2: Do not read from detached floppy

The Rev 3 firmware does not check floppy controller status before
commanding a sector read, which can lead to calling sim_disk_rdsect()
on a detached unit. With this checkin, the simulator will no longer
attempt a read or write if the floppy unit is not attached.
---
 3B2/3b2_if.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/3B2/3b2_if.c b/3B2/3b2_if.c
index bf2119c2..e3d3c0f4 100644
--- a/3B2/3b2_if.c
+++ b/3B2/3b2_if.c
@@ -554,6 +554,12 @@ void if_write(uint32 pa, uint32 val, size_t size)
         if_state.cmd = (uint8) val;
         /* Writing to the command register always de-asserts the IRQ line */
         if_clear_irq();
+
+        if ((uptr->flags & UNIT_ATT) == 0) {
+            /* If not attached, do nothing */
+            break;
+        }
+
         if_handle_command();
         break;
     case IF_TRACK_REG: