// FDC uses IRQ6 = int 26h
#define I_FDC	0x26
#define IRQ_FDC	6

// FDC regs (primary ctrlr)
#define FDC_STAT_A	0x0
#define FDC_STAT_B	0x1
#define FDC_DOR		0x2
#define FDC_TAPE	0x3
#define FDC_MSR_DSR	0x4
#define FDC_DATA	0x5
#define FDC_CCR_DIR	0x7

// FDC cmds
#define FDC_READ_TRACK	0x02
#define FDC_SPECIFY	0x03
#define FDC_SENSE_STAT	0x04
#define FDC_WRITE_DATA	0x05
#define FDC_READ_DATA	0x06
#define FDC_RECALIBRATE	0x07
#define FDC_SENSE_INTR	0x08
#define FDC_WRITE_DEL	0x09
#define FDC_READ_ID	0x0A
#define FDC_READ_DEL	0x0C
#define FDC_FMT_TRACK	0x0D
#define FDC_DUMP_REG	0x0E
#define FDC_SEEK	0x0F
#define FDC_VERSION	0x10
#define FDC_SCAN_EQL	0x11
#define FDC_PERP_MODE	0x12
#define FDC_CONFIGURE	0x13
#define FDC_LOCK	0x14
#define FDC_VERIFY	0x16
#define FDC_SCAN_LO_EQL	0x19
#define FDC_SCAN_HI_EQL	0x1D

// Motor stuff
#define FDC_MOTOR_OFF	0
#define FDC_MOTOR_ON	1
#define FDC_MOTOR_WAIT	2

// Read/write directions
#define FDC_DIR_READ	0
#define FDC_DIR_WRITE	1

// Digital Output Register (DOR) flags

// DOR motor control flags: 1 = on, 0 = off
#define FDC_DOR_MOTD	0x80 // Drive D
#define FDC_DOR_MOTC	0x40 // Drive C
#define FDC_DOR_MOTB	0x20 // Drive B
#define FDC_DOR_MOTA	0x10 // Drive A

// other DOR flags
#define FDC_DOR_DMA	0x08 // DMA2/IRQ6 On/Off
#define FDC_DOR_REST	0x04 // Controller Reset: this is active low; 1 = normal, 0 = reset

// DOR drive select (DOR & 0x03): selects drive 0-3

// Main Status Register (MSR) flags
#define FDC_MSR_RQM	0x80 // Main Request: 1 = ready, 0 = not ready
#define FDC_MSR_DIO	0x40 // Data In/Out: 1 = FDC -> PC, 0 = PC -> FDC
#define FDC_MSR_NDMA	0x20 // Non-DMA: 1 = DMA off, 0 = DMA on
#define FDC_MSR_BUSY	0x10 // Device busy: self-explanatory

// MSR drive seek flags: 1 = seeking, 0 = idle
#define FDC_MSR_ACTD	0x08 // Drive D
#define FDC_MSR_ACTC	0x04 // Drive C
#define FDC_MSR_ACTB	0x02 // Drive B
#define FDC_MSR_ACTA	0x01 // Drive A

// Status Register 0 (ST0) flags

/* ST0 interrupt code (ST0 & 0xC0):
    00 = normal termination
    01 = abnormal termination
    10 = invalid cmd
    11 = abnormal termination by poilling (drive became not ready)
*/

#define FDC_ST0_SEEK_END	0x20 // Seek End: seek/calibration completed
#define FDC_ST0_UNIT_CHK	0x10 // Unit Check: drive encountered a fault or recalibration failed
#define FDC_ST0_NOT_RDY		0x08 // Not Ready: self-explanatory
#define FDC_ST0_HEAD		0x04 // Active Head

// ST0 unit select (ST0 & 0x03): same fmt as DOR drive select

// Status Register 1 (ST1) flags
#define FDC_ST1_END_CYL		0x80 // End of Cylinder: set when sector count > sectors on track
// 0x40 is unused
#define FDC_ST1_DATA_ERR	0x20 // Data Error: set when an error is detected in a sector's data or ID fields
#define FDC_ST1_TIMEOUT		0x10 // Timeout: set when a data overrun occurs (i.e. the system is not reading data fast enough)
// 0x08 is unused
#define FDC_ST1_NO_DATA		0x04 // No Data: set when either a sector cannot be read, or an ID cannot be successfully read, or if the sector sequence cannot be determined
#define FDC_ST1_NO_WRITE	0x02 // Not Writable: set when attempting to write to a write-protected disk
#define FDC_ST1_NO_ID		0x01 // No Addr. Mark: set when an ID/(deleted) data address mark cannot be found.

// Status Register 2 (ST2) flags