Month: August 2001

This little kernel extension allows using hard drives with more than 128MB on a Macintosh Cube. It does so by setting the flags for ATA6 inside the driver.

This project is available at GitHub.

enableATA6.h

#include <IOKit/IOService.h>
#include "IOATABlockStorageDriver.h"

class com_sarnau_enableATA6 : public IOATABlockStorageDriver
{
    OSDeclareDefaultStructors ( com_sarnau_enableATA6 )

protected:
    virtual IOReturn    identifyAndConfigureATADevice ( void );
};

enableATA6.cpp

#include "enableATA6.h"

#define super IOATABlockStorageDriver
OSDefineMetaClassAndStructors ( com_sarnau_enableATA6, IOATABlockStorageDriver );

/***
*  This kext overloads the standard IOATABlockStorageDriver (by having a IOProbeScore of 1000)
*
*  We only have to overload the identifyAndConfigureATADevice function and patch a variable
*  to enable LBA support. The problem is the IOATABusInfo class - this class checks the bus
*  interface hardware and detects that the computer is not capable of supporting LBA drives.
*  And so LBA support is disabled in general. There is a good reason to do this, because without
*  this support in the ROM the system can't read the kernel from the drive, if the kernel is
*  beyond the 128MB border. For this reason we should partition a drive and make sure that the
*  boot partition is 127.99 GB or smaller. If we don't boot from this drive, we don't have to
*  partition it.
***/
IOReturn    com_sarnau_enableATA6::identifyAndConfigureATADevice(void)
{
    // call super class (and execute IDENTIFY DEVICE commamd - see ATA6 spec for more information)
    IOReturn    err = super::identifyAndConfigureATADevice();

    // does the drive support the 48 bit command set?
    if(fDeviceIdentifyData[kATAIdentifyCommandSetSupported2] & kATASupports48BitAddressingMask)
    {
        // and is the 48 bit command set really enabled for that drive?
        if(fDeviceIdentifyData[kATAIdentifyCommandsEnabled] & kATASupports48BitAddressingMask)
        {
            // then force the use of the LBA commands in the driver
            fUseExtendedLBA = true;

            // set the "48-bit LBA supported" bit in the "ATA Features" entry in the registry
            // (this seems not to be necessary, but maybe 3rd party software checks the registry)
            fSupportedFeatures |= kIOATAFeature48BitLBA;

            // we don't increase the buffer size, which is normally done by the super class
            // when a LBA drive is recognized. So we are limited to 256 instead of 2048 blocks
            // per read or write.
        }
    }

    return err;
}