/**
 * =========================================================================
 * File        : pmt.cpp
 * Project     : 0 A.D.
 * Description : Timer implementation using ACPI PM timer
 * =========================================================================
 */

// license: GPL; see lib/license.txt

#include "precompiled.h"
#include "pmt.h"

#include "lib/sysdep/win/win.h"
#include "lib/sysdep/acpi.h"
#include "lib/sysdep/win/mahaf.h"
#include "lib/bits.h"

#pragma pack(push,1)
struct FADT
{
    AcpiTable header;
    u8 unused[40];
    u32 pmTimerPortAddress;
    u8 unused2[32];
    u32 flags;
};
#pragma pack(pop)

static const u32 TMR_VAL_EXT = BIT(8);

//-----------------------------------------------------------------------------

LibError CounterPMT::Activate()
{
    if(!mahaf_Init())
        return ERR::FAIL;   // NOWARN (no Administrator privileges)
    if(!acpi_Init())
        WARN_RETURN(ERR::FAIL);
    // (note: it's called FADT, but the signature is "FACP")
    const FADT* fadt = (const FADT*)acpi_GetTable("FACP");
    if(!fadt)
        WARN_RETURN(ERR::NO_SYS);
    m_portAddress = u16_from_larger(fadt->pmTimerPortAddress);

    return INFO::OK;
}

void CounterPMT::Shutdown()
{
    acpi_Shutdown();
    mahaf_Shutdown();
}

bool CounterPMT::IsSafe() const
{
    // the PMT has one issue: "Performance counter value may unexpectedly
    // leap forward" (Q274323). This happens on some buggy Pentium-era
    // systems under heavy PCI bus load. We are clever and observe that
    // the TSC implementation would be used on such systems (because it
    // has higher precedence and is safe on P5 CPUs), so the PMT is fine
    // in general.
    return true;
}

u64 CounterPMT::Counter() const
{
    return mahaf_ReadPort32(m_portAddress);
}

/**
 * WHRT uses this to ensure the counter (running at nominal frequency)
 * doesn't overflow more than once during CALIBRATION_INTERVAL_MS.
 **/
uint CounterPMT::CounterBits() const
{
    // (see previous acpi_GetTable call)
    const FADT* fadt = (const FADT*)acpi_GetTable("FACP");
    debug_assert(fadt); // Activate made sure FADT is available
    const uint counterBits = (fadt->flags & TMR_VAL_EXT)? 32 : 24;
    return counterBits;
}

/**
 * initial measurement of the tick rate. not necessarily correct
 * (e.g. when using TSC: wcpu_ClockFrequency isn't exact).
 **/
double CounterPMT::NominalFrequency() const
{
    return (double)PMT_FREQ;
}