From fed171ff4d93dd3f8df15e70b8a6e8c9479f0350 Mon Sep 17 00:00:00 2001
From: OBattler <oubattler@gmail.com>
Date: Thu, 18 Apr 2024 03:50:48 +0200
Subject: [PATCH] IBM PS/1 Model 2121 FDC fix.

---
 src/floppy/fdc.c        | 16 +++++++++++++++-
 src/include/86box/fdc.h |  3 +++
 src/machine/m_ps1.c     |  2 +-
 3 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/src/floppy/fdc.c b/src/floppy/fdc.c
index 491df2f47..1a0aa2f10 100644
--- a/src/floppy/fdc.c
+++ b/src/floppy/fdc.c
@@ -780,7 +780,7 @@ fdc_write(uint16_t addr, uint8_t val, void *priv)
             }
             return;
         case 4:
-            if (!(fdc->flags & FDC_FLAG_PS1)) {
+            if (!(fdc->flags & FDC_FLAG_NO_DSR_RESET)) {
                 if (!(val & 0x80)) {
                     timer_set_delay_u64(&fdc->timer, 8 * TIMER_USEC);
                     fdc->interrupt = -6;
@@ -2608,6 +2608,20 @@ const device_t fdc_at_ps1_device = {
     .config        = NULL
 };
 
+const device_t fdc_at_ps1_2121_device = {
+    .name          = "PC/AT Floppy Drive Controller (PS/1, PS/2 ISA)",
+    .internal_name = "fdc_at_ps1",
+    .flags         = 0,
+    .local         = FDC_FLAG_NO_DSR_RESET | FDC_FLAG_DISKCHG_ACTLOW | FDC_FLAG_AT | FDC_FLAG_PS1,
+    .init          = fdc_init,
+    .close         = fdc_close,
+    .reset         = fdc_reset,
+    { .available = NULL },
+    .speed_changed = NULL,
+    .force_redraw  = NULL,
+    .config        = NULL
+};
+
 const device_t fdc_at_smc_device = {
     .name          = "PC/AT Floppy Drive Controller (SM(s)C FDC37Cxxx)",
     .internal_name = "fdc_at_smc",
diff --git a/src/include/86box/fdc.h b/src/include/86box/fdc.h
index 00de511f3..9529fde5c 100644
--- a/src/include/86box/fdc.h
+++ b/src/include/86box/fdc.h
@@ -55,6 +55,8 @@ extern int fdc_type;
 #define FDC_FLAG_SEC            0x1000 /* Is Secondary */
 #define FDC_FLAG_TER            0x2000 /* Is Tertiary */
 #define FDC_FLAG_QUA            0x3000 /* Is Quaternary */
+#define FDC_FLAG_CHANNEL        0x3000 /* Channel mask */
+#define FDC_FLAG_NO_DSR_RESET   0x4000 /* Has no DSR reset */
 
 typedef struct fdc_t {
     uint8_t dor;
@@ -251,6 +253,7 @@ extern const device_t fdc_at_ter_device;
 extern const device_t fdc_at_qua_device;
 extern const device_t fdc_at_actlow_device;
 extern const device_t fdc_at_ps1_device;
+extern const device_t fdc_at_ps1_2121_device;
 extern const device_t fdc_at_smc_device;
 extern const device_t fdc_at_ali_device;
 extern const device_t fdc_at_winbond_device;
diff --git a/src/machine/m_ps1.c b/src/machine/m_ps1.c
index e0a15126e..34691773f 100644
--- a/src/machine/m_ps1.c
+++ b/src/machine/m_ps1.c
@@ -378,7 +378,7 @@ ps1_setup(int model)
         if (gfxcard[0] == VID_INTERNAL)
             device_add(&ibm_ps1_2121_device);
 
-        device_add(&fdc_at_ps1_device);
+        device_add(&fdc_at_ps1_2121_device);
 
         device_add(&ide_isa_device);