分类： LINUX
2010-07-28 13:13:07
ATAPI refers to devices that use the Packet Interface of the ATA6 (or higher) standard command set. It is basically a way to issue SCSI commands to a CDROM, CD-RW, DVD, or tape drive, attached to the ATA bus.
ATAPI uses a very small number of ATA commands. The most important are the PACKET command (0xA0), and IDENTIFY PACKET DEVICE (0xA1).
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Each ATAPI command packet is made of a 'command byte' (from the SCSI command set -- see below for a partial list), followed by 11 'data' bytes. For instance, reading the table of contents is achieved by sending the following byte string to the device, as a "command".
unsigned char atapi_readtoc[]= { 0x43 /* ATAPI_READTOC */, 0, 1, 0, 0, 0, 0, 0, 12, 0x40, 0, 0};
The ATA PACKET command works in three phases, in PIO mode.
Phase 1) Set up the standard ATA IO port registers with ATAPI specific values. Then Send the ATA PACKET command to the device exactly as you would with any other ATA command: outb (ATA Command Register, 0xA0)
Phase 2) Prepare to do a PIO data transfer, the normal way, to the device. When the device is ready (BSY clear, DRQ set) you send the ATAPI command string (like the one above) as a 6 word PIO transfer to the device.
Phase 3) Wait for an IRQ. When it arrives, you must read the LBA Mid and LBA High IO port registers. They tell you the packet byte count that the ATAPI drive will send to you, or must receive from you. In a loop, you transmit that number of bytes, then wait for the next IRQ.
In DMA mode, only the first two phases happen. The device handles the details of phase 3 itself, with the PCI drive controller.
This command is a "normal" ATA PIO mode command, used during initialization. It is an exact mirror of the ATA IDENTIFY command, except that it only returns information about ATAPI devices. Use it in exactly the same way as you use IDENTIFY, including the meanings of all the bits in all the 256 words of data returned.
A data CDROM stores data in an ISO 9660 filesystem. A DVD may store data in a UDF or RockRidge filesystem. An AudioCD (CD-DA) stores data in a Joliet filesystem. To support these devices, you need to support the filesystems in your VFS code. That is the hard part. Making the driver work is relatively easy.
Important note: on the Primary bus, the standard set of ATA IO ports is 0x1F0 through 0x1F7. In much or all of the ATAPI documentation, you will see this set of IO ports called the "Task File". The term seems very confusing.
First, you need to have a buffer. If it is going to be a DMA buffer, it needs to follow the PRD rules (see the ATA/ATAPI using DMA article). If it is going to be a PIO buffer, then you need to know the size of the buffer. Call this size "maxByteCount". It must be an unsigned word, and 0 is illegal for PIO mode. A value of zero is mandatory for DMA mode, no matter what size the PRD buffers are.
Assume that the command is in words Command1 through Command6. Device is the Primary slave. Select the target device by setting the master/slave bit in the Device Select Register. There are no other bits needed.
outb (0x1F6, slavebit<<4)
If the command is going to use DMA, set the Features Register to 1, otherwise 0 for PIO.
outb (0x1F1, isDMA)
The Sectorcount Register and LBA Low Register are unused currently. Send maxByteCount in LBA Mid and LBA High Registers.
outb (0x1F4, (maxByteCount & 0xff)) outb (0x1F5, (maxByteCount >> 8))
Send the ATAPI PACKET command to the Command Register
outb (0x1F7, 0xA0)
Wait for an IRQ, or poll for BSY to clear and DRQ to set.
Then send the ATAPI command as 6 words, to the data port.
outw (0x1F0, Command1) outw (0x1F0, Command2) outw (0x1F0, Command3) outw (0x1F0, Command4) outw (0x1F0, Command5) outw (0x1F0, Command6)
Then wait for another IRQ. You cannot poll.
If this was a DMA command (isDMA == 1), then you are done. When the IRQ arrives, the transfer is complete.
If it was a PIO command, when the IRQ arrives, read the LBA Mid and LBA High Registers. This is vital. You told the drive the maximum amount of data to transfer at one time. Now the drive has to tell you the actual transfer size.
Once you have the transfer size (bytecount = LBA High << 8 | LBA Mid), do the PIO transfer.
wordcount = bytecount/2;
loop on inw(0x1F0) or outw(0x1f0) wordcount times.
If the transfer is complete, BSY and DRQ will clear. Otherwise, wait for the next IRQ, and read or write the same number of words again.
Notes: there is a possible future change planned to increase the length of ATAPI command strings to 8 words. Check the two bottom bits of ATAPI Identify word 0 to verify 6 or 8 word command size.
Once again, if you use polling to check BSY, DRQ, and ERR after sending the PACKET command, then you should probably ignore the ERR bit for the first four loops. (ATAPI calls this the "CHECK" bit, instead of ERR, but it means the same thing.)
| SCSI Command Name | Command Byte (OpCode) |
|---|---|
| TEST UNIT READY | 0x00 |
| REQUEST SENSE | 0x03 |
| FORMAT UNIT | 0x04 |
| INQUIRY | 0x12 |
| START STOP UNIT | 0x1B |
| PREVENT ALLOW MEDIUM REMOVAL | 0x1E |
| READ FORMAT CAPACITIES | 0x23 |
| READ CAPACITY | 0x25 |
| READ (10) | 0x28 |
| WRITE (10) | 0x2A |
| SEEK (10) | 0x2B |
| WRITE AND VERIFY (10) | 0x2E |
| VERIFY (10) | 0x2F |
| SYNCHRONIZE CACHE | 0x35 |
| WRITE BUFFER | 0x3B |
| READ BUFFER | 0x3C |
| READ TOC/PMA/ATIP | 0x43 |
| GET CONFIGURATION | 0x46 |
| GET EVENT STATUS NOTIFICATION | 0x4A |
| READ DISC INFORMATION | 0x51 |
| READ TRACK INFORMATION | 0x52 |
| RESERVE TRACK | 0x53 |
| SEND OPC INFORMATION | 0x54 |
| MODE SELECT (10) | 0x55 |
| REPAIR TRACK | 0x58 |
| MODE SENSE (10) | 0x5A |
| CLOSE TRACK SESSION | 0x5B |
| READ BUFFER CAPACITY | 0x5C |
| SEND CUE SHEET | 0x5D |
| REPORT LUNS | 0xA0 |
| BLANK | 0xA1 |
| SECURITY PROTOCOL IN | 0xA2 |
| SEND KEY | 0xA3 |
| REPORT KEY | 0xA4 |
| LOAD/UNLOAD MEDIUM | 0xA6 |
| SET READ AHEAD | 0xA7 |
| READ (12) | 0xA8 |
| WRITE (12) | 0xAA |
| READ MEDIA SERIAL NUMBER / SERVICE ACTION IN (12) | 0xAB / 0x01 |
| GET PERFORMANCE | 0xAC |
| READ DISC STRUCTURE | 0xAD |
| SECURITY PROTOCOL OUT | 0xB5 |
| SET STREAMING | 0xB6 |
| READ CD MSF | 0xB9 |
| SET CD SPEED | 0xBB |
| MECHANISM STATUS | 0xBD |
| READ CD | 0xBE |
| SEND DISC STRUCTURE | 0xBF |
Here is an example adapted from a working driver implementation.
/* The default and seemingly universal sector size for CD-ROMs. */ #define ATAPI_SECTOR_SIZE 2048 /* The default ISA IRQ numbers of the ATA controllers. */ #define ATA_IRQ_PRIMARY 0x0E #define ATA_IRQ_SECONDARY 0x0F /* The necessary I/O ports, indexed by "bus". */ #define ATA_DATA(x) (x) #define ATA_FEATURES(x) (x+1) #define ATA_SECTOR_COUNT(x) (x+2) #define ATA_ADDRESS1(x) (x+3) #define ATA_ADDRESS2(x) (x+4) #define ATA_ADDRESS3(x) (x+5) #define ATA_DRIVE_SELECT(x) (x+6) #define ATA_COMMAND(x) (x+7) #define ATA_DCR(x) (x+0x206) /* device control register */ /* valid values for "bus" */ #define ATA_BUS_PRIMARY 0x1F0 #define ATA_BUS_SECONDARY 0x170 /* valid values for "drive" */ #define ATA_DRIVE_MASTER 0xA0 #define ATA_DRIVE_SLAVE 0xB0 /* ATA specifies a 400ns delay after drive switching -- often * implemented as 4 Alternative Status queries. */ #define ATA_SELECT_DELAY(bus) \ {inb(ATA_DCR(bus));inb(ATA_DCR(bus));inb(ATA_DCR(bus));inb(ATA_DCR(bus));} /* Use the ATAPI protocol to read a single sector from the given * bus/drive into the buffer using logical block address lba. */ int atapi_drive_read_sector (uint32 bus, uint32 drive, uint32 lba, uint8 *buffer) { /* 0xA8 is READ SECTORS command byte. */ uint8 read_cmd[12] = { 0xA8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }; uint8 status; int size; /* Tell the scheduler that this process is using the ATA subsystem. */ ata_grab (); /* Select drive (only the slave-bit is set) */ outb (drive & (1 << 4), ATA_DRIVE_SELECT (bus)); ATA_SELECT_DELAY (bus); /* 400ns delay */ outb (0x0, ATA_FEATURES (bus)); /* PIO mode */ outb (ATAPI_SECTOR_SIZE & 0xFF, ATA_ADDRESS2 (bus)); outb (ATAPI_SECTOR_SIZE >> 8, ATA_ADDRESS3 (bus)); outb (0xA0, ATA_COMMAND (bus)); /* ATA PACKET command */ while ((status = inb (ATA_COMMAND (bus))) & 0x80) /* BUSY */ asm volatile ("pause"); while (!((status = inb (ATA_COMMAND (bus))) & 0x8) && !(status & 0x1)) asm volatile ("pause"); /* DRQ or ERROR set */ if (status & 0x1) { size = -1; goto cleanup; } read_cmd[9] = 1; /* 1 sector */ read_cmd[2] = (lba >> 0x18) & 0xFF; /* most sig. byte of LBA */ read_cmd[3] = (lba >> 0x10) & 0xFF; read_cmd[4] = (lba >> 0x08) & 0xFF; read_cmd[5] = (lba >> 0x00) & 0xFF; /* least sig. byte of LBA */ /* Send ATAPI/SCSI command */ outsw (ATA_DATA (bus), (uint16 *) read_cmd, 6); /* Wait for IRQ that says the data is ready. */ schedule (); /* Read actual size */ size = (((int) inb (ATA_ADDRESS3 (bus))) << 8) | (int) (inb (ATA_ADDRESS2 (bus))); /* This example code only supports the case where the data transfer * of one sector is done in one step. */ ASSERT (size == ATAPI_SECTOR_SIZE); /* Read data. */ insw (ATA_DATA (bus), buffer, size / 2); /* The controller will send another IRQ even though we've read all * the data we want. Wait for it -- so it doesn't interfere with * subsequent operations: */ schedule (); /* Wait for BSY and DRQ to clear, indicating Command Finished */ while ((status = inb (ATA_COMMAND (bus))) & 0x88) asm volatile ("pause"); cleanup: /* Exit the ATA subsystem */ ata_release (); return size; }
A medium is any media inserted in the ATAPI Drive, like a CD or a DVD. By using the 'SCSI Read Capacity' command, you can read the last LBA of the medium, then you calculate the medium's capacity using this relationship:
Capacity = (Last LBA + 1) * Block Size;
Last LBA and Block Size are returned after processing the command. Almost all CDs and DVDs use blocks with size of 2KB each.
Processing this command goes in the following algorithm:
The ATAPI packet should be in this formulation:
| bit→ ↓byte |
7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|---|---|---|---|---|---|---|---|---|
| 0 | Operation code = 25h | |||||||
| 1 | LUN | Reserved | RelAdr | |||||
| 2 | LBA (MSB) LBA (LSB) | |||||||
| 3 | ||||||||
| 4 | ||||||||
| 5 | ||||||||
| 6 | Reserved | |||||||
| 7 | Reserved | |||||||
| 8 | Reserved | PMI | ||||||
| 9 | Control | |||||||
The special control fields in the CDB have the following meaning:
The target will return capacity data structured as follows:
| bit→ ↓byte |
7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|---|---|---|---|---|---|---|---|---|
| 0–3 | Returned LBA | |||||||
| 4–7 | Block length in bytes | |||||||
If there is an error after polling, there may be no medium inserted, so this command may be also used to detect whether there is a medium or not, and if there is a medium, its capacity is read.
Quoting The Guide to ATA/ATAPI documentation (stanford.edu)
Hosts control ATAPI devices using SCSI command packets. The SCSI command packets are transported over the ATA interface, instead of the parallel SCSI bus. This cool hack is described in ATA/ATAPI-6. The set of SCSI command packets applicable to all SCSI devices is described in the . Again, ATAPI devices don't implement all of these, so it's best to consult the associated ATAPI spec for a device. CD-ROM command packets were originally described in . This document contains many inaccuracies in its description of the ATA bus interface, so please double check any statements against ATA/ATAPI-6. (Unfortunately, some of those inaccuracies were implemented!)