Initial contribution of the Adaptation Documentation.
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<concept id="GUID-E0DCBDCF-C056-53E5-A375-778327F848E4" xml:lang="en"><title>Asic Class Tutorial</title><shortdesc>Provides a work through tutorial that allows you to port
an Asic implementation to the template variant. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
<p id="GUID-39010DA3-632A-5C27-92BF-9AA8B5966EAB"> This tutorial
describes how to implement the Asic class. This is a pure virtual
interface that is defined and called by the Kernel, but which must
be implemented by the ASSP/Variant. The tutorial assumes that the
ASSP/Variant is split into an ASSP layer and a Variant layer. </p>
<p>For a minimal port, it isn't necessary to provide implementations
for the entire <xref href="GUID-A83A7C3C-7DC0-3B9C-842F-70FCC751365D.dita"><apiname>Asic</apiname></xref> class to be able to test that
the kernel boots, provided that those functions that are not fully
implemented have a dummy function so that the code will build. </p>
<p>The <codeph>Asic</codeph> class is defined in<filepath>..\e32\include\kernel\arm\assp.h</filepath>. For reference, the definition is: </p>
<codeblock id="GUID-B33CCD29-C6D2-5DC9-9302-A265E248E8DF" xml:space="preserve">class Asic
{
public:
// initialisation
virtual TMachineStartupType StartupReason()=0;
virtual void Init1()=0;
virtual void Init3()=0;
// debug
virtual void DebugOutput(TUint aChar)=0;
// power management
virtual void Idle()=0;
// timing
virtual TInt MsTickPeriod()=0;
virtual TInt SystemTimeInSecondsFrom2000(TInt& aTime)=0;
virtual TInt SetSystemTimeInSecondsFrom2000(TInt aTime)=0;
virtual TUint32 NanoWaitCalibration()=0;
// HAL
virtual TInt VariantHal(TInt aFunction, TAny* a1, TAny* a2)=0;
// Machine configuration
virtual TPtr8 MachineConfiguration()=0;
};</codeblock>
<p>Taking the template port as a concrete example, the ASSP layer
implementation of the <xref href="GUID-A83A7C3C-7DC0-3B9C-842F-70FCC751365D.dita"><apiname>Asic</apiname></xref> class is defined and
implemented by the <codeph>TemplateAssp</codeph> class, and the Variant
implemention is defined and implemented by the <codeph>Template</codeph> class. </p>
<section id="GUID-7F5D4AD6-0881-5942-9A86-A95C02125A28"><title>Asic::Init1()
implementation</title> <p><b>Entry conditions</b> </p> <ul>
<li id="GUID-6B761E80-7B63-5F96-9852-65F7321D365B"><p>called in the
context of the initial (null) thread </p> </li>
<li id="GUID-B8211B76-1308-5372-8034-4B1B9CFE58F3"><p>interrupts are
disabled </p> </li>
<li id="GUID-482B5E00-A25F-5966-90FB-B622F9C1AF99"><p>there is no
kernel heap </p> </li>
<li id="GUID-6D985E4B-1A69-58B6-975D-7F696BB062C3"><p>memory management
functions are not available. </p> </li>
</ul> <p><b>What the function should do</b> </p> <p>This is called during
stage 1 of kernel initialisation. </p> <p>In this function, you need
to: </p> <ul>
<li id="GUID-D156866C-0BA0-58AE-9438-C4D1D2628D67"><p>initialise the
real time clock </p> </li>
<li id="GUID-7FB60E9E-938C-515E-803D-27DA1315040C"><p>initialise the
interrupt dispatcher before CPU interrupts are enabled. </p> </li>
<li id="GUID-D55DD2D9-3E45-5256-B1F4-E583706AED66"><p>set the threshold
values for cache maintenance. You can set separate values for: </p> <ul>
<li id="GUID-B3CEB2A4-4849-517F-A0E9-76A6018537B8"><p>purging (invalidating)
a cache </p> </li>
<li id="GUID-9DE85DFB-D789-565C-A944-EFBF987D457C"><p>cleaning a cache </p> </li>
<li id="GUID-0C638F72-1D6B-512D-88EB-7369240C776A"><p>flushing (i.e.
cleaning and invalidating) a cache. </p> </li>
</ul> <p>You use the <xref href="GUID-4425E698-EE8A-369B-92CD-09B1CBD2911F.dita#GUID-4425E698-EE8A-369B-92CD-09B1CBD2911F/GUID-81AA7412-9754-3020-9D77-14DEDD3196CA"><apiname>Cache::SetThresholds()</apiname></xref> interface
to set these values. </p> <p>As an example of what the threshold values
mean, if you purge a memory region from cache, and the size of that
region is greater than the threshold value, then the entire cache
is purged. If the size of that region is less than or equal to to
the threshold value, then only the region is purged. </p> <p>The threshold
values are platform specific, and you need to choose your values based
on your own performance measurements. Symbian cannot make recommendations.
If you choose not to set your own values, Symbian platform supplies
a set of default values, which are set by <codeph>Cache::Init1()</codeph>. </p> <p>Note that there is also a <xref href="GUID-4425E698-EE8A-369B-92CD-09B1CBD2911F.dita#GUID-4425E698-EE8A-369B-92CD-09B1CBD2911F/GUID-2DBD79A7-2061-3B89-89FA-B0DFC7AFFCF9"><apiname>Cache::GetThresholds()</apiname></xref> interface that you may find useful. </p> </li>
<li id="GUID-DA94E963-6AA5-5084-8C19-77B7AD484A44"><p>set up the RAM
zones. For details, see the <xref href="GUID-C376486D-B9BF-5D00-8B1A-1527FC1F83AD.dita">RAM Zone Tutorial</xref>. </p> </li>
</ul> <p>Typically, you would also initialise any memory devices not
initialised by the bootstrap. Any other initialisation that must happen
early on should also be done here. </p> <p>The kernel calls the Variant's <codeph>Init1()</codeph> function. On the template port, this is the Variant
layer's <codeph>Init1()</codeph>, i.e. the functions <codeph>Template::Init1()</codeph>. The source for this is in <filepath>...\template_variant\specific\variant.cpp</filepath>. </p> <codeblock id="GUID-E1247A9A-B7F7-5C0F-BD3B-A0E471FA4654" xml:space="preserve">void Template::Init1()
{
__KTRACE_OPT(KBOOT,Kern::Printf("Template::Init1()"));
//
// TO DO: (mandatory)
//
// Configure Memory controller and Memrory Bus parameters (in addition to what was done in the Bootstrap)
//
__KTRACE_OPT(KBOOT,Kern::Printf("Memory Configuration done"));
//
// TO DO: (optional)
//
// Inform the kernel of the RAM zone configuration via Epoc::SetRamZoneConfig().
// For devices that wish to reduce power consumption of the RAM IC(s) the callback functions
// RamZoneCallback() and DoRamZoneCallback() will need to be implemented and passed
// to Epoc::SetRamZoneConfig() as the parameter aCallback.
// The kernel will assume that all RAM ICs are fully intialised and ready for use from boot.
//
//
// TO DO: (optional)
//
// Initialise other critical hardware functions such as I/O interfaces, etc, not done by Bootstrap
//
// if CPU is Sleep-capable, and requires some preparation to be put in that state (code provided in Bootstrap),
// the address of the idle code is writen at this location by the Bootstrap
// e.g.
// iIdleFunction=*(TLinAddr*)((TUint8*)&Kern::SuperPage()+0x1000);
//
TemplateAssp::Init1();
}</codeblock> <p>The last line is a call into the ASSP layer,
which is implemented as shown below. On the template port, it is the
ASSP layer that initialises the interrupt dispatcher and the real
time clock. The source for this is in <filepath>...\template_assp\assp.cpp</filepath>: </p> <codeblock id="GUID-1E90071E-6CB0-5B01-984C-AFCFD095CA64" xml:space="preserve">EXPORT_C void TemplateAssp::Init1()
{
__KTRACE_OPT(KBOOT,Kern::Printf("TemplateAssp::Init1()"));
//
// TO DO: (optional)
//
TemplateInterrupt::Init1(); // initialise the ASSP interrupt controller
//
// TO DO: (optional)
//
// Initialises any hardware blocks which require early initialisation, e.g. enable and power the LCD, set up
// RTC clocks, disable DMA controllers. etc.
//
}
</codeblock> <p> <codeph>TemplateInterrupt::Init1();</codeph> is
static function that initialises the interrupt dispatcher. See <xref href="GUID-423537D5-2C8A-5C26-8D7B-60446E95F681.dita">Interrupt Layer Initialisation</xref>. </p> </section>
<section id="GUID-F5275882-BBD0-561F-B617-683AA2004BB9"><title>Asic::Init3()
implementation</title> <p><b>Entry conditions</b> </p> <ul>
<li id="GUID-9450694C-ADF3-52DE-AA58-4AFF53A1EEC6"><p>called in the
context of the supervisor thread </p> </li>
<li id="GUID-335F8A2E-0223-598E-AA23-F72E3BE84D76"><p>the kernel is
ready to handle interrupts </p> </li>
<li id="GUID-B198D669-9E88-5279-81A8-6A11F8EE3BFD"><p>the kernel heap
and memory management system is fully functional. </p> </li>
</ul> <p><b>What the function should do</b> </p> <p>This is called during
stage 3 of kernel initialisation. </p> <p>In this function, you need
to: </p> <ul>
<li id="GUID-38C35732-E79A-595C-9852-12D1FE30A081"><p>enable interrupt
sources </p> </li>
<li id="GUID-D4F750D9-96B1-5AD1-AA66-2485D37B6323"><p>start the millisecond
tick timer. </p> </li>
<li id="GUID-390278B7-EF0F-59ED-A57D-54490655C97B"><p>Optionally,
replace the implementation used by <codeph>Kern::NanoWait()</codeph>. </p> </li>
</ul> <p>Any other general initialisation can also be done here. </p> <p>As an example, on the template port, the function is implemented
in the Variant layer, by <codeph>Template::Init3()</codeph>. </p> <p><b>Millisecond tick timer</b> </p> <p>The kernel expects that the
kernel's tick handler routine will be called at a fixed microsecond
period, the value of which is returned by the implementation of <xref href="GUID-E0DCBDCF-C056-53E5-A375-778327F848E4.dita#GUID-E0DCBDCF-C056-53E5-A375-778327F848E4/GUID-917B420D-5F10-5190-97D2-9D2DAFD4FB76">Asic::MsTickPeriod()</xref> function. The <codeph>Init3()</codeph> function must be implemented to start this. See <xref href="GUID-F84E18B8-5883-5A3A-A9DB-EC25BB86149F.dita">Kernel Timers</xref> for background information. </p> <p>The template implementation
is as follows: </p> <codeblock id="GUID-AF60AC52-5188-5911-9A03-A090D048ADA3" xml:space="preserve">EXPORT_C void TemplateAssp::Init3()
{
__KTRACE_OPT(KBOOT,Kern::Printf("TemplateAssp::Init3()"));
TTemplate::Init3();
NTimerQ& m=*(NTimerQ*)NTimerQ::TimerAddress();
iTimerQ=&m;
//
// TO DO: (mandatory)
//
// If Hardware Timer used for System Ticks cannot give exactly the period required store the initial rounding value
// here which is updated every time a match occurs. Note this leads to "wobbly" timers whose exact period change
// but averages exactly the required value
// e.g.
// m.iRounding=-5;
//
TInt r=Interrupt::Bind(KIntIdOstMatchMsTimer,MsTimerTick,&m); // bind the System Tick interrupt
if (r!=KErrNone)
Kern::Fault("BindMsTick",r);
//
// TO DO: (mandatory)
//
// Clear any pending OST interrupts and enable any OST match registers.
// If possible may reset the OST here (to start counting from a full period). Set the harwdare to produce an
// interrupt on full count
//
r=Interrupt::Enable(KIntIdOstMatchMsTimer); // enable the System Tick interrupt
if (r!=KErrNone)
Kern::Fault("EnbMsTick",r);
//
// TO DO: (optional)
//
// Allocate physical RAM for video buffer, as per example below. However with some hardware, the Video Buffer
// may not reside in main System memory, it may be dedicated memory.
//
// EXAMPLE ONLY
TInt vSize=VideoRamSize();
r=Epoc::AllocPhysicalRam(2*vSize,TemplateAssp::VideoRamPhys);
if (r!=KErrNone)
Kern::Fault("AllocVRam",r);
}</codeblock> <p><b>Servicing the timer interrupt</b> </p> <p>The timer interrupt
service routine is required only to call the <xref href="GUID-DFEAC0DA-E384-3249-BF6A-529A76C3AC34.dita#GUID-DFEAC0DA-E384-3249-BF6A-529A76C3AC34/GUID-DA340CB0-C334-3C17-B903-14B135ABDCF1"><apiname>Ntimer::TickQ()</apiname></xref> function and perform any housekeeping necessary to ensure that the
handler itself is called again after the time reported by the <xref href="GUID-BCFC62D6-B87A-3319-8DA7-4BA64A9D0311.dita"><apiname>MsTickPeriod()</apiname></xref> routine. Since the handler is called frequently,
it is written in assembler for the fastest execution. </p> <codeblock id="GUID-0770E505-10F8-582C-BCAA-BC99074FD906" xml:space="preserve">__NAKED__ void MsTimerTick(TAny* aPtr)
{
// Service 1ms tick interrupt
asm("ldr ip, [r0, #%a0]" : : "i" _FOFF(NTimerQ,iRounding));
asm("ldr r2, __KHwBaseOst ");
asm("adds ip, ip, #2 ");
asm("ldr r3, __KOst1000HzTickMatchIncrement ");
asm("subcs ip, ip, #5 ");
asm("str ip, [r0, #%a0]" : : "i" _FOFF(NTimerQ,iRounding));
asm("addcs r3, r3, #1 ");
asm("mov r1, #%a0" : : "i" ((TInt)(1<<KHwOstMatchMsTimer)));
asm("str r1, [r2, #0x14] "); // clear interrupt
asm("ldr r1, [r2, #%a0]" : : "i" ((TInt)KHwOstMatchMsTimer*4)); // r1=old match value
asm("add r1, r1, r3 "); // step match value on
asm("ldr ip, [r2, #0x10] "); // r3=system timer value
asm("str r1, [r2, #%a0]" : : "i" ((TInt)KHwOstMatchMsTimer*4));
asm("cmp ip, r1 "); // compare to next match value
#ifdef _DEBUG
asm("addpl r1, ip, #10 "); // in DEBUG if timer>match value, set match value to timer + a bit
asm("strpl r1, [r2, #%a0]" : : "i" ((TInt)KHwOstMatchMsTimer*4));
asm("b Tick__7NTimerQ "); // call interrupt handler anyway
#else
asm("bmi Tick__7NTimerQ "); // if timer<match value, OK - call interrupt handler
#endif
// otherwise we are late for the next tick so force a data abort exception...
asm("mvn r2, #0x10000002 "); // r2=0xeffffffd
asm("str r2, [r2] "); // die
// Constant data embedded in code.
asm("__KOst1000HzTickMatchIncrement: ");
asm(".word %a0" : : "i" ((TInt)KOst1000HzTickMatchIncrement));
asm("__KHwBaseOst: ");
asm(".word %a0" : : "i" ((TInt)KHwBaseOst));
}</codeblock> <p>Note that it is a requirement that the timer
period should be an integral number of microseconds, even if the exact
period is not 1000us. It is always possible to add code to the interrupt
handler to achieve this average so that over a large number of ticks,
the deviation from this average will tend to 0, by adjusting the exact
number of ticks from tick to tick. See also <xref href="GUID-F84E18B8-5883-5A3A-A9DB-EC25BB86149F.dita">Timers</xref></p> <p><b>NanoWait() implementation</b> </p> <p> <xref href="GUID-C6946ECB-775F-3EC2-A56F-78F25B9FBE3D.dita#GUID-C6946ECB-775F-3EC2-A56F-78F25B9FBE3D/GUID-0EEAFE45-5C0D-32A9-AD64-CE3AB0AEE6B3"><apiname>Kern::NanoWait()</apiname></xref> is a function that can be called if you want to wait for very short
periods of time within the kernel. You call this function and specify
the number of nanoseconds. The function is, in effect, a shell that
uses default implementation code provided by the generic platform.
You can provide your own implementation in your port, and register
this with the platform. This allows the wait functionality to be implemented
in the best possible way for your platform, possibly by using a hardware
timer whose frequency is independent of the CPU frequency. </p> <p>To replace the default implementation, you need to: </p> <ul>
<li id="GUID-733329E1-99C5-56A4-B80F-FFCFD74F1320"><p>code your own
function. This has the same signature as <codeph>Kern::NanoWait()</codeph>: </p> <codeblock id="GUID-0AC0DC75-38C7-58A8-8A4F-4C5AA8F23A80" xml:space="preserve">void AsicImpl::DoNanoWait(TUint32 aInterval)
{
// Wait for aInterval nanoseconds
}</codeblock> <p>where <codeph>AsicImpl</codeph> is the class that is ultimately derived from <codeph>Asic</codeph>. </p> </li>
<li id="GUID-BDE8C5D6-6E6C-5B2E-9219-A8D5DC114EA2"><p>register this
implementation by adding the following call into your <codeph>Asic::Init3()</codeph> function: </p> <codeblock id="GUID-1A99C7D2-A550-5B39-9AE7-559AE7B13C3E" xml:space="preserve">Kern::SetNanoWaitHandler(AsicImpl::DoNanoWait);</codeblock> </li>
</ul> <p>You can see where this goes by looking at the template port
at: <filepath>...\base\cedar\template\template_assp\template_assp.cpp</filepath> </p> </section>
<section id="GUID-1028F2D0-BA8B-4880-9565-50C89EBD1685"><title>Asic::DebugOutput()
implementation</title> <p>It is worth implementing this early so that
it is possible to get trace output to see what the kernel is doing.
This function is passed one character at a time. Normally this is
sent to a UART, though it can be output through any convenient communications
channel. </p> <p>On the template port, this is implemented in the
Variant layer, by <codeph>Template::DebugOutput()</codeph> in <filepath>...\template_variant\specific\variant.cpp</filepath>. </p> </section>
<section id="GUID-EEC48040-B7D7-406B-8138-4A1F646ED990"><title>Asic::Idle()
implementation</title> <p>If no power management has been implemented,
then this function is called when the system is to idle to allow power
saving. This function can just return, until power management is implemented.
Once power management has been implemented, then idling behaviour
will be handled by the power controller, i.e. the Variant's implementation
of the <xref href="GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366.dita"><apiname>DPowerController</apiname></xref> class </p> </section>
<section id="GUID-917B420D-5F10-5190-97D2-9D2DAFD4FB76"><title>Asic::MsTickPeriod()
implementation</title> <p>This function is used to return the number
of microseconds per tick. To avoid timing drift, a tick frequency
should be chosen that gives a round number of microseconds per tick.
The function can return zero until the tick timer has been implemented. </p> <p>On the template port, this function is implemented in the ASSP
layer, and can be found in the source file <filepath>...\template_assp\assp.cpp</filepath>. It is a simple function that just returns the value. </p> <codeblock id="GUID-C0D88A32-974C-5824-8D9D-A9B6D7C45802" xml:space="preserve">EXPORT_C TInt TemplateAssp::MsTickPeriod()
{
//
// TO DO: (mandatory)
//
// Return the OST tick period (System Tick) in microseconds ( 10E-06 s ).
//
return 1000; // EXAMPLE ONLY
}
</codeblock> <p>See also <xref href="GUID-F84E18B8-5883-5A3A-A9DB-EC25BB86149F.dita">Timers</xref>. </p> </section>
<section id="GUID-1C8A7F79-8CD5-442E-A9A5-925C94E80773"><title>Asic::SystemTimeInSecondsFrom2000()
implementation</title> <p>This is a function that the kernel
uses to get the system time. Its signature is </p> <codeblock id="GUID-A1FF9777-D627-5409-B6CD-02F20F7A1889" xml:space="preserve">Tint SystemTimeInSecondsFrom2000(Tint& aTime);</codeblock> <p>An implementation must set the <codeph>aTime</codeph> reference
to the number of seconds that have elapsed since the start of the
year 2000. This is a positive number; a negative number is interpreted
as time before 2000. </p> <p>For the template reference board, the
implementation is as follows: </p> <codeblock id="GUID-C4812A82-C069-564B-972A-0922EAC00AAB" xml:space="preserve">EXPORT_C TInt TemplateAssp::SystemTimeInSecondsFrom2000(TInt& aTime)
{
aTime=(TInt)TTemplate::RtcData();
__KTRACE_OPT(KHARDWARE,Kern::Printf("RTC READ: %d",aTime));
return KErrNone;
}
</codeblock> <p>Until a real time clock is implemented, this function
can just return <xref href="GUID-6CA4F1ED-7947-3087-B618-D35858FAA3BC.dita"><apiname>KErrNone</apiname></xref>. </p> <p>This function
calls the register access functions in the <codeph>TTemplate</codeph> class. See <filepath>...\template_assp\template_assp.cpp</filepath> for implementation details. </p> <p>Note that tracing output is
provided when the KHARDWARE bit in the kerneltrace flags is set for
the debug build. </p> </section>
<section id="GUID-F0AC3E98-345F-4491-9957-51B127437181"><title>Asic::SetSystemTimeInSecondsFrom2000()
implementation</title> <p>This is a function that the kernel uses
to set the system time. Its signature is </p> <codeblock id="GUID-B965C38C-A65E-5E54-BE09-C81300B59EDC" xml:space="preserve">Tint SetSystemTimeInSecondsFrom2000(Tint aTime);</codeblock> <p>This sets the real time clock to the number of seconds that have
elapsed since the start of the year 2000. This is a positive number;
a negative number is interpreted as time before 2000. </p> <p>For
the template reference board, the implementation is as follows: </p> <codeblock id="GUID-89BFC844-B053-51B7-9ACA-81B19E63414B" xml:space="preserve">EXPORT_C TInt TemplateAssp::SetSystemTimeInSecondsFrom2000(TInt aTime)
{
//
// TO DO: (optional)
//
// Check if the RTC is running and is stable
//
__KTRACE_OPT(KHARDWARE,Kern::Printf("Set RTC: %d",aTime));
TTemplate::SetRtcData(aTime);
__KTRACE_OPT(KHARDWARE,Kern::Printf("RTC: %d",TTemplate::RtcData()));
return KErrNone;
}
</codeblock> <p>Note that tracing output is provided when the KHARDWARE
bit in the kerneltrace flags is set for the debug build. In this function,
the trace output shows the value passed in from the kernel and then
shows the value read back from the real time clock for verification. </p> </section>
<section id="GUID-50BB6924-899F-4385-879E-19A2FC68657C"><title>Asic::NanoWaitCalibration()
implementation</title> <p>The function <xref href="GUID-C6946ECB-775F-3EC2-A56F-78F25B9FBE3D.dita#GUID-C6946ECB-775F-3EC2-A56F-78F25B9FBE3D/GUID-0EEAFE45-5C0D-32A9-AD64-CE3AB0AEE6B3"><apiname>Kern::NanoWait()</apiname></xref> can be called if you want to wait for very short periods of time
within the kernel. You call this function and specify the number of
nanoseconds. You can either use the default implementation of this
function, or you can provide your own. </p> <p>The default implementation
provided by Symbian platform that <codeph>Kern::NanoWait()</codeph> uses is a busy loop that is calibrated by calling <codeph>Asic::NanoWaitCalibration()</codeph>. <codeph>NanoWaitCalibration()</codeph> should return the number
of nanoseconds taken to execute 2 machine cycles. This is obviously
dependent on the CPU clock speed, so if variants are likely to run
at different speeds, then this should be implemented in the Variant
layer. </p> <p>This approach cannot always take into account factors
such as processor frequency scaling. An alternative approach is for
the Variant to supply its own implementation to be used by <codeph>Kern::NanoWait()</codeph>. Note that you do not replace <codeph>Kern::NanoWait()</codeph> itself as this is a shell function that results in a call to the
the implementation. See <xref href="GUID-E0DCBDCF-C056-53E5-A375-778327F848E4.dita#GUID-E0DCBDCF-C056-53E5-A375-778327F848E4/GUID-F5275882-BBD0-561F-B617-683AA2004BB9">Asic::Init3()</xref> for detail on how to replace the implementation. </p> <p>On the template port, <codeph>Asic::NanoWaitCalibration()</codeph> is implemented in the ASSP layer, and not in the Variant layer,
and can be found in the source file <filepath>...\template_assp\assp.cpp</filepath>. It is a simple function that just returns the value. </p> <codeblock id="GUID-68298BF1-EAE7-507D-9B5B-DDACE6C19799" xml:space="preserve">EXPORT_C TUint32 TemplateAssp::NanoWaitCalibration()
{
//
// TO DO: (mandatory)
//
// Return the minimum time in nano-seconds that it takes to execute the following code:
// nanowait_loop:
// subs r0, r0, r1
// bhi nanowait_loop
//
// If accurate timings are required by the Base Port, then it should provide it's own implementation
// of NanoWait which uses a hardware counter. (See Kern::SetNanoWaitHandler)
//
return 0; // EXAMPLE ONLY
}
</codeblock> </section>
<section id="GUID-15F344C5-A1CC-45FC-AC94-27022A1DF448"><title>Asic::VariantHal()
implementation</title> <p>You might find it useful to review <xref href="GUID-9AE254D4-AA60-579E-8D9D-F2797106A413.dita">User-Side Hardware
Abstraction Technology</xref> first. </p> <p>This is the HAL handler
for the HAL group <xref href="GUID-66A851A0-2A0C-3624-AEC1-22F6629FABF7.dita#GUID-66A851A0-2A0C-3624-AEC1-22F6629FABF7/GUID-3FA061DE-68F8-3948-96B3-5AFC989DBDE1"><apiname>THalFunctionGroup::EHalGroupVariant</apiname></xref>. </p> </section>
<section id="GUID-2EEA143D-612C-47C5-B16C-22DAD1BC179E"><title>Asic::MachineConfiguration()
implementation</title> <p>This returns a <xref href="GUID-C0D29B11-1535-3D11-B318-B18D30A6120B.dita"><apiname>TPtr8</apiname></xref> descriptor representing an area containing machine configuration
information. </p> <p>The address of this object is obtained by calling <xref href="GUID-C6946ECB-775F-3EC2-A56F-78F25B9FBE3D.dita#GUID-C6946ECB-775F-3EC2-A56F-78F25B9FBE3D/GUID-4DAE5199-1EB0-31D1-BA06-8F47E96EEADE"><apiname>Kern::MachineConfig()</apiname></xref>. However, the Variant (either the
ASSP layer or the Variant layer or both) is responsible for the content. </p> <p>In the template port, the function is implemented in the Variant
layer: </p> <codeblock id="GUID-B75F631E-03DB-5C98-911F-1161842AA17F" xml:space="preserve">TPtr8 Template::MachineConfiguration()
{
return TPtr8((TUint8*)&Kern::MachineConfig(),sizeof(TActualMachineConfig),sizeof(TActualMachineConfig));
}
</codeblock> <p>Here, the machine configuration information is represented
by an object of type <codeph>TTemplateMachineConfig</codeph>, which
derives from <codeph>TMachineConfig</codeph>. In effect, <codeph>TMachineConfig</codeph> represents information that is common to all, while the Variant
can extend this to contain whatever information is appropriate. </p> <p>Note that <codeph>TActualMachineConfig</codeph> is a typedef
for <codeph>TTemplateMachineConfig</codeph>. </p> </section>
<section id="GUID-B1E39D8C-1562-4464-A316-144ED89935C9"><title>Asic::StartupReason()
implementation</title> <p>If a startup reason is available from hardware
or a preserved RAM location, it should be returned by the function.
The default is to return <codeph>EStartupColdReset</codeph>. </p> <p>On the template port, this is implemented in the ASSP layer: </p> <codeblock id="GUID-FC4FFA46-804D-5A7F-B7CA-DDDC72C60041" xml:space="preserve">EXPORT_C TMachineStartupType TemplateAssp::StartupReason()
{
__KTRACE_OPT(KBOOT,Kern::Printf("TemplateAssp::StartupReason"));
#ifdef _DEBUG // REMOVE THIS
TUint s = Kern::SuperPage().iHwStartupReason;
__KTRACE_OPT(KBOOT,Kern::Printf("CPU page value %08x", s));
#endif // REMOVE THIS
//
// TO DO: (mandatory)
//
// Map the startup reason read from the Super Page to one of TMachineStartupType enumerated values
// and return this
//
return EStartupCold; // EXAMPLE ONLY
}
</codeblock> </section>
</conbody><related-links>
<link href="GUID-984C2A0D-36BE-5A99-9D65-3F8791C669FF.dita#GUID-984C2A0D-36BE-5A99-9D65-3F8791C669FF/GUID-95C34114-F986-5428-9D40-5CF64429CDBD">
<linktext>ASSP/Variant Architecture</linktext></link>
</related-links></concept>