HAL Detection

bool acpi = false, apic = false, hpet = false;

/* Try to parse the ACPI tables */
rsdp_t *rddp = find_rsdp();
if (rsdp)
{
    acpi = true;

    < Parse the HPET table >

    if (There is an HPET)
    {
        hpet = true;
    }

    < Parse the MADT >

    if (There are multiple processors and APICs)
    {
        goto mp;
    }
    else if (There is an APIC, but not multiple processors)
    {
        apic = true;
        goto up;
    }
}

/* Try to parse the MP tables */
mp_table_ptr_t *mp_table_ptr = find_mp_table_ptr();
if (mp_table_ptr)
{
    goto mp;
}

/* If there's no ACPI or MP tables, we're uniprocessor, but use CPUID to detect an APIC */
< Detect an APIC >
if (There is an APIC)
{
    apic = true;
}

/* Uniprocessor HAL */
up:
    if (acpi)
    {
        if (apic)
        {
            if (hpet)
            {
                < Load the ACPI APIC and HPET HAL >
            }
            else
            {
                < Load the ACPI APIC and APIC timer HAL >
            }
        }
        else
        {
            < Load the ACPI 8259 and PIT HAL >
        }
    }
    else
    {
        if (apic)
        {
            < Load the legacy APIC and APIC timer HAL >
        }
        else
        {
            < Load the legacy 8259 and PIT HAL >
        }
    }
/* Multiprocessor */
mp:
    if (acpi)
    {
        if (hpet)
        {
            < Load the ACPI APIC and HPET HAL >
        }
        else
        {
            < Load the ACPI APIC and APIC timer HAL >
        }
    }
    else
    {
        < Load the legacy APIC and APIC timer HAL >
    }