ide: strip DSC (SERVICE) bit for ATAPI to fix Win9x CD Code 10 (MiSTer-devel#1221)

ide_set_regs() synthesizes status bit 4 as DSC for every device. For an
ATAPI (packet) device bit 4 is the SERVICE bit, not DSC, and since we never
run overlapped/queued commands it must read 0. 86Box masks DSC out of every
ATAPI status read and reports SERVICE=0 for a non-overlapped device. The
permanent SERVICE=1 made Win9x's ESDI_506 reject the channel (Device Manager
Code 10, "ESDI access to drive failed (IRQ?), so punting"), even though the
completion IRQ was delivered. Strip DSC for CD drives to match the reference.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: kblood

ide.cpp

@@ -162,6 +162,13 @@ void ide_set_regs(ide_config *ide)
 {
 	if (!(ide->regs.status & (ATA_STATUS_BSY | ATA_STATUS_ERR))) ide->regs.status |= ATA_STATUS_DSC;
 
+	// For ATAPI (packet) devices, status bit 4 is the SERVICE bit, not DSC. We never run
+	// overlapped commands, so SERVICE must read 0. Force it low for CD drives, matching 86Box
+	// ide_status() which masks DSC out of every ATAPI status read (hdc_ide.c). Win9x ESDI_506
+	// otherwise reads the permanent bit-4 as "overlapped-command SERVICE pending", rejects the
+	// channel, and the device fails to start (Device Manager Code 10).
+	if (ide->drive[ide->regs.drv].cd) ide->regs.status &= ~ATA_STATUS_DSC;
+
 	uint8_t data[12] =
 	{
 		(uint8_t)((ide->drive[ide->regs.drv].cd) ? 0x80 : ide->regs.io_size),