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NEC PC-9801-55 mode #377

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002bc92
Add Quirks flag for PC-9801-55
s-rakowski May 9, 2026
4747366
Add PC-9801-55 system preset
s-rakowski May 9, 2026
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3 changes: 2 additions & 1 deletion lib/SCSI2SD/include/scsi2sd.h
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Original file line number Diff line number Diff line change
Expand Up @@ -92,7 +92,8 @@ typedef enum
S2S_CFG_QUIRKS_XEBEC = 4,
S2S_CFG_QUIRKS_VMS = 8,
S2S_CFG_QUIRKS_X68000 = 16,
S2S_CFG_QUIRKS_EWSD = 32
S2S_CFG_QUIRKS_EWSD = 32,
S2S_CFG_QUIRKS_PC98_55 = 64
} S2S_CFG_QUIRKS;

typedef enum
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34 changes: 29 additions & 5 deletions lib/SCSI2SD/src/firmware/mode.c
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Expand Up @@ -402,6 +402,14 @@ static void doModeSense(
}
}

// The PC-9801-55 SCSI-1 controller, and its derivatives will
// ask for all pages (0x3F), expecting only those pages back:
// 0x01 - Read-write error recovery page
// 0x03 - Format device page
// 0x04 - Rigid disk geometry page
// This quirk is expected to be used with SCSI-1 mode only
uint8_t oldNecHddMode = scsiDev.target->cfg->quirks == S2S_CFG_QUIRKS_PC98_55;

////////////// Block Descriptor
////////////////////////////////////
if (!dbd)
Expand All @@ -410,9 +418,15 @@ static void doModeSense(
// Number of blocks
// Zero == all remaining blocks shall have the medium
// characteristics specified.
scsiDev.data[idx++] = 0;
scsiDev.data[idx++] = 0;
scsiDev.data[idx++] = 0;
uint32_t blocks = 0;
if (oldNecHddMode)
{
// NEC PC-9801-55 needs explicit block count
blocks = scsiDev.target->cfg->scsiSectors;
}
scsiDev.data[idx++] = (blocks >> 16) & 0xFF;
scsiDev.data[idx++] = (blocks >> 8) & 0xFF;
scsiDev.data[idx++] = blocks & 0xFF;

scsiDev.data[idx++] = 0; // reserved

Expand Down Expand Up @@ -440,7 +454,7 @@ static void doModeSense(
}
}

if (pageCode == 0x02 || pageCode == 0x3F)
if (!oldNecHddMode && (pageCode == 0x02 || pageCode == 0x3F))
{
pageFound = 1;
if ((scsiDev.compatMode >= COMPAT_SCSI2))
Expand All @@ -462,6 +476,16 @@ static void doModeSense(
pageIn(pc, idx, FormatDevicePage, sizeof(FormatDevicePage));
if (pc != 0x01)
{
if (oldNecHddMode)
{
// This mimics ArdSCSino-stm32 behavior,
// setting "Tracks per zone" to heads per cylinder value
// If left as 0, PC-9801FA doesn't detect the drive properly
scsiDev.data[idx+2] = 0x00;
scsiDev.data[idx+3] = scsiDev.target->cfg->headsPerCylinder;
// Interleave field
scsiDev.data[idx+15] = 0x00;
}
uint16_t sectorsPerTrack = scsiDev.target->cfg->sectorsPerTrack;
scsiDev.data[idx+10] = sectorsPerTrack >> 8;
scsiDev.data[idx+11] = sectorsPerTrack & 0xFF;
Expand Down Expand Up @@ -627,7 +651,7 @@ static void doModeSense(
}

// SCSI 2 standard says page 0 is always last.
if (pageCode == 0x00 || pageCode == 0x3F)
if (!oldNecHddMode && (pageCode == 0x00 || pageCode == 0x3F))
{
pageFound = 1;
pageIn(pc, idx, OperatingPage, sizeof(OperatingPage));
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2 changes: 2 additions & 0 deletions src/BlueSCSI.cpp
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Expand Up @@ -260,6 +260,8 @@ static const char * quirksToChar(int quirks)
{
switch (quirks)
{
case S2S_CFG_QUIRKS_PC98_55:
return "PC-9801-55";
case S2S_CFG_QUIRKS_APPLE:
return "Apple";
case S2S_CFG_QUIRKS_OMTI:
Expand Down
21 changes: 19 additions & 2 deletions src/BlueSCSI_settings.cpp
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Expand Up @@ -36,7 +36,7 @@
// SCSI system and device settings
BlueSCSISettings g_scsi_settings;

const char *systemPresetName[] = {"", "Mac", "MacPlus", "MPC3000", "MegaSTE", "X68000", "X68000-SCSI", "X68000-SASI", "NeXT", "Generic"};
const char *systemPresetName[] = {"", "Mac", "MacPlus", "MPC3000", "MegaSTE", "X68000", "X68000-SCSI", "X68000-SASI", "NeXT", "PC-9801-55", "Generic"};
const char *devicePresetName[] = {"", "ST32430N"};

// must be in the same order as bluescsi_speed_grade_t in BlueSCSI_settings.h
Expand Down Expand Up @@ -539,6 +539,14 @@ scsi_system_settings_t *BlueSCSISettings::initSystem(const char *presetName)
cfgSys.enableParity = false;
cfgSys.maxSyncSpeed = 5;
}
else if (strequals(systemPresetName[SYS_PRESET_PC_9801_55], presetName))
{
m_sysPreset = SYS_PRESET_PC_9801_55;
cfgSys.quirks = S2S_CFG_QUIRKS_PC98_55;
cfgSys.enableSCSI2 = false;
cfgDev.sectorsPerTrack = 25;
cfgDev.headsPerCylinder = 8;
}
else if (strequals(systemPresetName[SYS_PRESET_NeXT], presetName))
{
m_sysPreset = SYS_PRESET_NeXT;
Expand All @@ -558,7 +566,16 @@ scsi_system_settings_t *BlueSCSISettings::initSystem(const char *presetName)
}

// Clear SCSI device strings
memset(cfgDev.vendor, 0, sizeof(cfgDev.vendor));
if (m_sysPreset == SYS_PRESET_PC_9801_55)
{
// Controller requires that Vendor starts with "NEC"
const char *necVendor = "NECBLUE";
strncpy(cfgDev.vendor, necVendor, sizeof(cfgDev.vendor));
}
else
{
memset(cfgDev.vendor, 0, sizeof(cfgDev.vendor));
}
memset(cfgDev.prodId, 0, sizeof(cfgDev.prodId));
memset(cfgDev.revision, 0, sizeof(cfgDev.revision));
memset(cfgDev.serial, 0, sizeof(cfgDev.serial));
Expand Down
1 change: 1 addition & 0 deletions src/BlueSCSI_settings.h
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Expand Up @@ -62,6 +62,7 @@ typedef enum
SYS_PRESET_X68000_SCSI,
SYS_PRESET_X68000_SASI,
SYS_PRESET_NeXT,
SYS_PRESET_PC_9801_55,
SYS_PRESET_GENERIC,
} scsi_system_preset_t;

Expand Down
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