From 5e437fc7364d48fc50190c730685b87d6a324c74 Mon Sep 17 00:00:00 2001
From: SarahW <pcem@pcem-emulator.co.uk>
Date: Sat, 11 Apr 2020 14:47:19 +0100
Subject: [PATCH] Fallback to old MPU behaviour on SB cards. Fixes SB16/AWE32
 initialisation on Windows 3.1.

---
 src/sound_azt2316a.c    |  2 +-
 src/sound_mpu401_uart.c | 21 ++++++++++++++++-----
 src/sound_mpu401_uart.h |  4 +++-
 src/sound_sb.c          |  4 ++--
 4 files changed, 22 insertions(+), 9 deletions(-)

diff --git a/src/sound_azt2316a.c b/src/sound_azt2316a.c
index b5fda11..da41bce 100644
--- a/src/sound_azt2316a.c
+++ b/src/sound_azt2316a.c
@@ -1446,7 +1446,7 @@ void *azt_common_init(const int type, char *nvr_filename)
         io_sethandler(azt2316a->cur_addr+8, 0x0002, opl3_read,   NULL, NULL, opl3_write,   NULL, NULL, &azt2316a->sb->opl);
         io_sethandler(0x0388, 0x0004, opl3_read,   NULL, NULL, opl3_write,   NULL, NULL, &azt2316a->sb->opl);
         io_sethandler(azt2316a->cur_addr+4, 0x0002, sb_ct1345_mixer_read, NULL, NULL, sb_ct1345_mixer_write, NULL, NULL, azt2316a->sb);
-        mpu401_uart_init(&azt2316a->sb->mpu, azt2316a->cur_mpu401_addr, azt2316a->cur_mpu401_irq);
+        mpu401_uart_init(&azt2316a->sb->mpu, azt2316a->cur_mpu401_addr, azt2316a->cur_mpu401_irq, 1);
 
         azt2316a_create_config_word(azt2316a); // recreate even if we have read it from EEPROM, because we have some overrides (CD interfaces always off, etc)
         sound_add_handler(azt2316a_get_buffer, azt2316a);
diff --git a/src/sound_mpu401_uart.c b/src/sound_mpu401_uart.c
index 6ec3614..22cb638 100644
--- a/src/sound_mpu401_uart.c
+++ b/src/sound_mpu401_uart.c
@@ -31,16 +31,26 @@ static void mpu401_uart_write(uint16_t addr, uint8_t val, void *p)
                         // But actual behaviour is weird. For example, the MPU401 port test in the AZT1605 drivers for Windows NT
                         // want this to return an Ack but the IRQ test in the same driver wants this to raise no interrupts!
                         mpu->rx_data = 0xfe; /*Acknowledge*/
-                        mpu->status = STATUS_OUTPUT_NOT_READY;
                         mpu->uart_mode = 0;
-                        //mpu401_uart_raise_irq(p);
+                        if (mpu->is_aztech)
+                                mpu->status = STATUS_OUTPUT_NOT_READY;
+                        else
+                        {
+                                mpu->status = 0;
+                                mpu401_uart_raise_irq(p);
+                        }
                         break;
                         
                         case 0x3f: /*Enter UART mode*/
                         mpu->rx_data = 0xfe; /*Acknowledge*/
-                        mpu->status = STATUS_OUTPUT_NOT_READY;
                         mpu->uart_mode = 1;
-                        mpu401_uart_raise_irq(p);
+                        if (mpu->is_aztech)
+                        {
+                                mpu->status = STATUS_OUTPUT_NOT_READY;
+                                mpu401_uart_raise_irq(p);
+                        }
+                        else
+                                mpu->status = 0;
                         break;
                 }
                 return;
@@ -63,12 +73,13 @@ static uint8_t mpu401_uart_read(uint16_t addr, void *p)
         return mpu->rx_data;
 }
 
-void mpu401_uart_init(mpu401_uart_t *mpu, uint16_t addr, int irq)
+void mpu401_uart_init(mpu401_uart_t *mpu, uint16_t addr, int irq, int is_aztech)
 {
         mpu->status = STATUS_INPUT_NOT_READY;
         mpu->uart_mode = 0;
         mpu->addr = addr;
         mpu->irq = irq;
+        mpu->is_aztech = is_aztech;
         
         io_sethandler(addr, 0x0002, mpu401_uart_read, NULL, NULL, mpu401_uart_write, NULL, NULL, mpu);
 }
diff --git a/src/sound_mpu401_uart.h b/src/sound_mpu401_uart.h
index b133d80..9634d58 100644
--- a/src/sound_mpu401_uart.h
+++ b/src/sound_mpu401_uart.h
@@ -9,9 +9,11 @@ typedef struct mpu401_uart_t
         int uart_mode;
         uint16_t addr;
         int irq;
+        
+        int is_aztech;
 } mpu401_uart_t;
 
-void mpu401_uart_init(mpu401_uart_t *mpu, uint16_t addr, int irq);
+void mpu401_uart_init(mpu401_uart_t *mpu, uint16_t addr, int irq, int is_aztech);
 void mpu401_uart_update_addr(mpu401_uart_t *mpu, uint16_t addr);
 void mpu401_uart_update_irq(mpu401_uart_t *mpu, int irq);
 
diff --git a/src/sound_sb.c b/src/sound_sb.c
index e2aa7f3..08830d0 100644
--- a/src/sound_sb.c
+++ b/src/sound_sb.c
@@ -1052,7 +1052,7 @@ void *sb_16_init()
         io_sethandler(0x0388, 0x0004, opl3_read,   NULL, NULL, opl3_write,   NULL, NULL, &sb->opl);
         io_sethandler(addr+4, 0x0002, sb_ct1745_mixer_read, NULL, NULL, sb_ct1745_mixer_write, NULL, NULL, sb);
         sound_add_handler(sb_get_buffer_sb16, sb);
-        mpu401_uart_init(&sb->mpu, 0x330, -1);
+        mpu401_uart_init(&sb->mpu, 0x330, -1, 0);
 
 
         return sb;
@@ -1082,7 +1082,7 @@ void *sb_awe32_init()
         io_sethandler(0x0388, 0x0004, opl3_read,   NULL, NULL, opl3_write,   NULL, NULL, &sb->opl);
         io_sethandler(addr+4, 0x0002, sb_ct1745_mixer_read, NULL, NULL, sb_ct1745_mixer_write, NULL, NULL, sb);
         sound_add_handler(sb_get_buffer_emu8k, sb);
-        mpu401_uart_init(&sb->mpu, 0x330, -1);
+        mpu401_uart_init(&sb->mpu, 0x330, -1, 0);
         emu8k_init(&sb->emu8k, emu_addr, onboard_ram);
 
         return sb;