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Ilia Sharin aa72007e48 Added ATA/ATAPI article - dramatic story as always

2026-06-02 23:48:29 -04:00

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Gayle — IDE & PCMCIA Controller

Overview

Gayle is Commodore's custom gate-array chip providing ATA/IDE hard drive and PCMCIA Type II card slot interfaces. It appears in two models with different silicon revisions:

Model	Gayle ID	IDE	PCMCIA	Notes
A600	`$D0`	Yes (ECS system)	Yes	First Gayle implementation
A1200	`$D1`	Yes (AGA system)	Yes	Different byte-lane mapping

The CD32 does not have Gayle — its storage is handled by Akiko.

The A4000 uses a different IDE interface (directly on the motherboard, no Gayle chip).

Gayle Identification

The Gayle ID register shifts one bit per read access:

    move.b  $DA8000, d0     ; Read Gayle ID byte
    ; d0 = $D0 → A600 Gayle
    ; d0 = $D1 → A1200 Gayle

#define GAYLE_ID_ADDR  0xDA8000

volatile UBYTE *gayle_id = (UBYTE *)GAYLE_ID_ADDR;
UBYTE id_byte = *gayle_id;
/* $D0 = A600, $D1 = A1200 */

On machines without Gayle (A500, A2000, A3000, A4000, CD32), reading $DA8000 returns bus noise — always check before assuming Gayle is present.

Gayle Register Map

Address	Register	R/W	Description
`$DA8000`	`GAYLE_ID`	R	Chip ID (shifts on each read access)
`$DA9000`	`GAYLE_INT_STATUS`	RW	Interrupt status (IDE + PCMCIA)
`$DA9004`	`GAYLE_INT_ENABLE`	RW	Interrupt enable mask
`$DA9008`	`GAYLE_CONTROL`	RW	Control register (PCMCIA power, wait states)

IDE Interface

Register Maps — A600 vs A1200

The IDE registers are at base $DA0000 on both models. The critical difference is byte-lane mapping: the A1200 places 8-bit ATA registers on odd byte offsets within each 4-byte window, while the A600 uses even offsets.

A600 IDE Registers

Address	ATA Register	R/W
`$DA0000`	Data (16-bit)	RW
`$DA0004`	Error (R) / Features (W)	RW
`$DA0008`	Sector Count	RW
`$DA000C`	Sector Number (LBA 7:0)	RW
`$DA0010`	Cylinder Low (LBA 15:8)	RW
`$DA0014`	Cylinder High (LBA 23:16)	RW
`$DA0018`	Drive/Head (LBA 27:24)	RW
`$DA001C`	Status (R) / Command (W)	RW
`$DA101C`	Alternate Status / Device Control	RW

A1200 IDE Registers

Address	ATA Register	R/W
`$DA0000`	Data (16-bit)	RW
`$DA0005`	Error (R) / Features (W)	RW
`$DA0009`	Sector Count	RW
`$DA000D`	Sector Number (LBA 7:0)	RW
`$DA0011`	Cylinder Low (LBA 15:8)	RW
`$DA0015`	Cylinder High (LBA 23:16)	RW
`$DA0019`	Drive/Head (LBA 27:24)	RW
`$DA001D`	Status (R) / Command (W)	RW
`$DA101D`	Alternate Status / Device Control	RW

Important

The A1200 byte-lane offset (+1 from A600) is because Gayle maps 8-bit ATA registers on the odd byte lane of the 16-bit Amiga bus. IDE drivers must account for this — a single driver cannot blindly use the same offsets for both machines. Check the Gayle ID first.

PIO Data Transfer

IDE data transfers use 16-bit word access to the Data register:

; Read one sector (512 bytes = 256 words) from IDE
; a0 = destination buffer

    lea     $DA0000, a1         ; IDE data register
    move.w  #255, d0            ; 256 words
.read_loop:
    move.w  (a1), (a0)+         ; read word from IDE → buffer
    dbf     d0, .read_loop

PCMCIA Interface

Both A600 and A1200 support a Type II PCMCIA (PC Card) slot:

Address Range	Type	Description
`$600000`–`$9FFFFF`	Attribute memory	Card CIS (Card Information Structure)
`$A00000`–`$A3FFFF`	Common memory	Data / I/O window
`$A40000`–`$A7FFFF`	Common memory (cont.)	Extended data area

Card Insertion Sequence

Card insertion triggers GAYLE_IRQ_CD (card detect interrupt)
Software reads CIS from attribute memory at $600000 to identify card type
Parse CONFIG tuple for card configuration
For ATA cards (CompactFlash in PCMCIA adapter): configure as IDE device
For network/modem cards: use card-specific I/O mapping
For SRAM cards: map as block device (up to 4 MB)

Interrupt Handling

Interrupt Routing

Gayle routes all its interrupts through CIA-A /FLG pin → CIAICRF_FLG → CPU IPL 6 (INT6).

Interrupt Status Bits

/* $DA9000 GAYLE_INT_STATUS — read to check, write 0 to clear */
#define GAYLE_IRQ_IDE    (1<<7)  /* IDE drive interrupt (A1200) */
                                  /* bit 6 on A600 */
#define GAYLE_IRQ_CARD   (1<<6)  /* PCMCIA card interrupt */
#define GAYLE_IRQ_BVD1   (1<<5)  /* PCMCIA battery voltage detect 1 */
#define GAYLE_IRQ_BVD2   (1<<4)  /* PCMCIA battery voltage detect 2 */
#define GAYLE_IRQ_WP     (1<<3)  /* PCMCIA write protect */
#define GAYLE_IRQ_CD     (1<<2)  /* PCMCIA card detect */

Warning

The IDE interrupt bit position differs between A600 and A1200 Gayle revisions. Always check the Gayle ID register before masking interrupt bits.

Interrupt Service Routine

; Gayle ISR (INT6 handler)
gayle_isr:
    move.b  $DA9000, d0         ; read GAYLE_INT_STATUS
    btst    #7, d0              ; IDE interrupt? (A1200)
    beq.s   .check_pcmcia
    
    ; Handle IDE interrupt
    move.b  $DA001D, d1         ; read ATA status to clear INTRQ
    bclr    #7, $DA9000         ; clear Gayle IDE IRQ
    bra.s   .done
    
.check_pcmcia:
    btst    #6, d0              ; PCMCIA interrupt?
    beq.s   .done
    ; Handle PCMCIA...
    bclr    #6, $DA9000         ; clear PCMCIA IRQ
    
.done:
    rte

PCMCIA Power Control

Gayle controls PCMCIA card power (5V standard; 3.3V on A1200 rev 1D+):

/* $DA9008 GAYLE_CONTROL bits */
#define GAYLE_POW   (1<<7)  /* PCMCIA power on/off */
#define GAYLE_WS    (1<<6)  /* Wait states for PCMCIA access */

AmigaOS IDE Access

AmigaOS accesses Gayle IDE through the standard device driver stack:

Application → dos.library → File System Handler → scsi.device / ata.device → Gayle IDE

Applications never access Gayle registers directly:

/* Standard file access — no direct Gayle interaction */
BPTR fh = Open("DH0:myfile", MODE_NEWFILE);
Write(fh, data, length);
Close(fh);

The A600 uses scsi.device from Kickstart ROM. The A1200 uses ata.device (also called ide.device in some OS versions) which includes A1200-specific byte-lane handling.

References

Commodore A600 Technical Reference Manual — Gayle chapter
Commodore A1200 Technical Reference Manual — Gayle chapter
NDK39: community-documented Gayle registers (no official header)
ADCD 2.1: scsi.device / ata.device Autodocs
Big Book of Amiga Hardware — Gayle pinout and board photos

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