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<!-- Date:        2003/07/15                                         -->
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<part id="hal-m68k-mcfxxxx"><title>Freescale MCFxxxx Variant Support</title>

<refentry id="m68k-mcfxxxx">
  <refmeta>
    <refentrytitle>MCFxxxx ColdFire Processors</refentrytitle>
  </refmeta>
  <refnamediv>
    <refname><varname>CYGPKG_HAL_M68K_MCFxxxx</varname></refname>
    <refpurpose>eCos Support for Freescale MCFxxxx Processors</refpurpose>
  </refnamediv>

  <refsect1 id="m68k-mcfxxxx-description"><title>Description</title>
    <para>
The Freescale ColdFire family is a range of processors including the
MCF5206 and the MCF5282. From a programmer's perspective these
processors all share basically the same processor core, albeit with
minor differences in the instruction set. They differ in areas like
performance, on-chip peripherals and caches. Even when it comes to
peripherals there is a lot of commonality. For example many but not
all Coldfire processors use the same basic interrupt controller(s) as
the MCF5282. Similarly the on-chip UARTs tend to use the same basic
design although there are variations in the number of UARTs, the fifo
sizes, and in certain details.
    </para>
    <para>
    The MCFxxxx variant HAL package
<varname>CYGPKG_HAL_M68K_MCFxxxx</varname> provides support for
various features that are common to many but not all Coldfire
processors. This includes HAL diagnostics via an on-chip UART and
interrupt controller management for those processors which have
MCF5282-compatible controllers. The variant HAL complements the M68K
architectural HAL package. An eCos configuration should also include a
processor-specific HAL package such as
<varname>CYGPKG_HAL_M68K_MCF5272</varname> to support the
chip-specific peripherals and cache details, and a platform HAL
package such as <varname>CYGPKG_HAL_M68K_M5272C3</varname> to support
board-level details like external memory chips. The processor or
platform HAL can override the functionality provided by the variant
HAL.
    </para>
  </refsect1>

  <refsect1 id="m68k-mcfxxxx-config"><title>Configuration</title>
    <para>
The MCFxxxx variant HAL package should be loaded automatically when
eCos is configured for appropriate target hardware. It should never be
necessary to load this package explicitly. Unloading the package
should only happen as a side effect of switching target hardware.
    </para>
    <para>
On most ColdFire platforms the variant HAL will provide the HAL
diagnostics support via one of the UARTs. Some platforms may provide
their own HAL diagnostics facility, for example output via an LCD. The
variant HAL diagnostics support is active if the processor or platform
implements the
<varname>CYGINT_HAL_M68K_MCFxxxx_DIAGNOSTICS_USE_DEFAULT</varname>
interface. It is also active only in configurations which do not rely
on an underlying rom monitor such as RedBoot:
if <varname>CYGSEM_HAL_USE_ROM_MONITOR</varname> is enabled then the
default diagnostics channel will automatically be inherited from
RedBoot. The variant HAL then provides a number of configuration
options related to diagnostics:
    </para>
    <variablelist>
      <varlistentry>
        <term><varname>CYGHWR_HAL_M68K_MCFxxxx_DIAGNOSTICS_PORT</varname></term>
        <listitem><para>
This selects the destination for HAL diagnostics. The number of UARTs
available depends on the processor, and on any given board some of the
UARTs may not be connected. Hence the variant HAL looks for
configuration options
<varname>CYGHWR_HAL_M68K_MCFxxxx_UART0</varname>, 
<varname>CYGHWR_HAL_M68K_MCFxxxx_UART1</varname> and
<varname>CYGHWR_HAL_M68K_MCFxxxx_UART2</varname> to see which on-chip
UARTs are actually available on the processor and target hardware, and
uses this information to let the user select a UART.
        </para>
        <para>
When a UART is in use as the HAL diagnostics channel, that UART
should not be used for any other purpose. In particular application
code should avoid using it for I/O via the serial driver.
        </para></listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>CYGNUM_HAL_M68K_MCFxxxx_DIAGNOSTICS_BAUD</varname></term>
        <listitem><para>
When a UART is selected for HAL diagnostics this option specifies the
default baud rate. The most common setting is 38400. That provides a
compromise between performance and reliability, especially in
electrically noisy environments such as an industrial environment or a
test farm. Some platforms may define
<varname>CYGNUM_HAL_M68K_MCFxxxx_DIAGNOSTICS_DEFAULT_BAUD</varname>
to handle scenarios where another default baud rate is preferable,
typically for compatibility with existing software.
        </para></listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>CYGNUM_HAL_M68K_MCFxxxx_DIAGNOSTICS_ISRPRI</varname></term>
        <listitem><para>
Usually the HAL diagnostics channel is driven in polled mode but in
some scenarios interrupts are required. For example, when debugging an
application over a serial line on top of the gdb stubs provided by
RedBoot, the user should be able to interrupt the application with a
control-C. The application will not be polling the HAL diagnostics
UART at this point so instead the eCos interrupt management code
interacts with the gdb stubs to do the right thing. This configuration
option selects the interrupt priority. It should be noted that on some
processors with MCF5282-compatible interrupt controllers all
priorities for enabled interrupts should be unique, and it is the
responsibility of application developers to ensure this condition is
satisfied. 
        </para></listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1 id="m68k-mcfxxxx-port"><title>The HAL Port</title>
    <para>
This section describes how the MCFxxxx variant HAL package implements
parts of the eCos HAL specification. It should be read in conjunction
with similar sections from the architectural and processor HAL
documentation.
    </para>

    <refsect2 id="m68k-mcfxxxx-port-io"><title>HAL I/O</title>
      <para>
The <filename class="headerfile">cyg/hal/var_io.h</filename> header
provides various definitions for on-chip peripherals, where the
current processor has peripherals compatible with the MCF5282's.
This header is automatically included by the architectural
<filename class="headerfile">cyg/hal/hal_io.h</filename> so other
packages and application code will usually only include the latter.
      </para>
      <para>
It is up to the processor HAL to specify exactly what <filename
class="headerfile">var_io.h</filename> should export. For example the
MCF5213's <filename class="headerfile">proc_io.h</filename> header
contains the following:
      </para>
      <programlisting width=72>
# define HAL_MCFxxxx_HAS_MCF5282_INTC               1
# define HAL_MCFxxxx_INTC0_BASE                     (HAL_MCF521x_IPSBAR + 0x00000C00)
      </programlisting>
      <para>
This enables support within the variant HAL for a single
MCF5282-compatible interrupt controller, and cases <filename
class="headerfile">var_io.h</filename> to export symbols such as:
      </para>
      <programlisting width=72>
#ifdef HAL_MCFxxxx_HAS_MCF5282_INTC
// Two 32-bit interrupt mask registers
# define HAL_MCFxxxx_INTCx_IMRH                     0x0008
# define HAL_MCFxxxx_INTCx_IMRL                     0x000C
&hellip;
# define HAL_MCFxxxx_INTCx_ICRxx_IL_MASK            (0x07 << 3)
# define HAL_MCFxxxx_INTCx_ICRxx_IL_SHIFT           3
      </programlisting>
      <para>
Symbols such as <varname>HAL_MCFxxxx_INTCx_IMRH</varname> can be used
to access the relevant hardware registers via
<function>HAL_READ_UINT32</function> and
<function>HAL_WRITE_UINT32</function>. Symbols like
<varname>HAL_MCFxxxx_INTCx_ICRxx_IL_MASK</varname> can be used to
generate or decode the contents of the hardware registers.
      </para>
      <para>
The header file does mostly use a naming convention, but is not
guaranteed to be totally consistent. There may also be discrepancies
with the documentation because the manuals for the various Coldfire
processors are not always consistent about their naming schemes.
All I/O definitions provided by the variant HAL will start with
<literal>HAL_MCFxxxx_</literal>, followed by the name of the
peripheral. If a peripheral is likely to be a singleton, for example
an on-chip flash unit, then the name is unadorned. If there may be
several instances of the peripheral then the name will be followed by
a lower case x. For example:
      </para>
      <programlisting width=72>
# define HAL_MCFxxxx_CFM_CR                         0x0000
&hellip;
# define HAL_MCFxxxx_UARTx_UMR                      0x00
      </programlisting>
      <para>
Register names will be relative to some base address such as
<varname>HAL_MCFxxxx_CFM_BASE</varname> or
<varname>HAL_MCFxxxx_UART0_BASE</varname>, so code accessing a
register would look like:
      </para>
      <programlisting width=72>
    HAL_READ_UINT32(HAL_MCFxxxx_CFM_BASE + HAL_MCFxxxx_CFM_PROT, reg);
    &hellip;
    HAL_WRITE_UINT8(base + HAL_MCFxxxx_UARTx_UTB, '*');
      </programlisting>
      <para>
Usually the register names are singletons, but in some cases such as
the interrupt controller priority registers there may be multiple
instances of the register and the names will be suffixed
appropriately. For example
<varname>HAL_MCFxxxx_INTCx_ICRxx_IL_MASK</varname> indicates the field
<literal>IL</literal> within one of the <literal>ICR</literal>
registers within one of the interrupt controllers.
      </para>
      <para>
As mentioned earlier the processor HAL's <filename
class="headerfile">proc_io.h</filename> will control which definitions
are exported by <filename class="headerfile">var_io.h</filename>.
Sometimes the processor HAL will then go on to undefine or redefine
some of the symbols, to reflect incompatibilities between the
processor's devices and the equivalent devices on the MCF5282. There
may also be additional symbols for the devices, and there will be
additional definitions for any processor-specific hardware. In
particular GPIO pin handling is handled by the processor HAL, not by
the variant HAL. Application developers should examine <filename
class="headerfile">proc_io.h</filename> as well as
<filename class="headerfile">var_io.h</filename> and the
processor-specific documentation to see exactly what I/O definitions
are provided. When porting to a new Coldfire processor it is best to
start with an existing processor HAL and copy
code as appropriate. A search for <literal>_HAS_</literal> in
<filename class="headerfile">var_io.h</filename> will also be
informative.
      </para>
    </refsect2>

    <refsect2 id="m68k-mcfxxxx-port-context"><title>Thread Contexts and Setjmp/Longjmp</title>
      <para>
All MCFxxxx processors support interrupts and exceptions in a uniform
way. When an interrupt or exception occurs the hardware pushes the
current program counter, the status register, and an additional 16-bit
word containing information about the interrupt source, for a total of
64 bits. Hence the PCSR part of a thread context consists of two
32-bit integers, and the variant HAL provides appropriate C and
assembler macros to examine and manipulate these.
      </para>
      <para>
Not all MCFxxxx processors have hardware floating point, so support
for this is left to the processor HAL package. Some MCFxxxx processors
have additional hardware units such as a multiply-accumulator, but
these are not currently supported by eCos.
      </para>
    </refsect2>

    <refsect2 id="m68k-mcfxxxx-port-diag"><title>HAL Diagnostics</title>
      <para>
The various MCFxxxx processors usually have one or more UARTs based on
very similar hardware. The variant HAL package can provide HAL
diagnostic support using such a UART. There are some minor differences
such as fifo sizes, and the UARTs will be accessed at different memory
locations. These differences are handled by a small number of macros
provided by the processor and platform HAL.
      </para>
      <para>
The MCFxxxx variant HAL only provides HAL diagnostic support via a
UART if the processor or platform HAL does not provide an alternative
implementation. That copes with situations where the on-chip UARTs are
not actually accessible on the target board and an alternative
communication channel must be used.
      </para>
      <para>
If the variant HAL should implement HAL diagnostics then the processor
or platform HAL should implement the CDL interface
<varname>CYGINT_HAL_M68K_MCFxxxx_DIAGNOSTICS_USE_DEFAULT</varname>. It
should also define one or more of
<varname>CYGHWR_HAL_M68K_MCFxxxx_UART0</varname>,
<varname>CYGHWR_HAL_M68K_MCFxxxx_UART1</varname> and
<varname>CYGHWR_HAL_M68K_MCFxxxx_UART2</varname>, and ensure that any
multi-purpose GPIO pins are set correctly. The variant HAL will take
care of the rest.
      </para>
    </refsect2>

    <refsect2 id="m68k-mcfxxxx-port-cache"><title>Cache Handling</title>
      <para>
The various MCFxxxx processors all have very different caches, so
support for these is deferred to the processor HAL.
      </para>
    </refsect2>

    <refsect2 id="m68k-mcfxxxx-port-exceptions"><title>Exceptions</title>
      <para>
All MCFxxxx processors support synchronous exceptions in a uniform
way, with the hardware pushing sufficient information on to the stack
to identify the nature of the exception. This means that the architectural
entry point <function>hal_m68k_exception_vsr</function> can be used as
the default VSR for all exceptions, with no need for separate
trampoline functions.
      </para>
      <para>
The variant HAL does not provide any special support for recovering
from exceptions.
      </para>
    </refsect2>

    <refsect2 id="m68k-mcfxxxx-port-interrupts"><title>Interrupts</title>
      <para>
All MCFxxxx processors supports interrupts in a uniform way. When an
interrupt occurs the hardware pushes sufficient information on to the
stack to identify the interrupt. Therefore the architectural entry
point <function>hal_m68k_interrupt_vsr</function> can be used as the
default VSR for all interrupts, with the variant just supplying a
small number of macros that allow the generic code to extract details of
the interrupt source. There is no need for separate trampoline
functions for every interrupt source.
      </para>
      <para>
On processors which have MCF5282-compatible interrupt and edge port
modules the variant HAL can provide the
<function>HAL_INTERRUPT_MASK</function>,
<function>HAL_INTERRUPT_UNMASK</function>,
<function>HAL_INTERRUPT_SET_LEVEL</function>,
<function>HAL_INTERRUPT_ACKNOWLEDGE</function> and
<function>HAL_INTERRUPT_CONFIGURE</function> macros. There is support
for processors with a single interrupt controller or with two separate
interrupt controllers. Otherwise these macros are left to the
processor HAL. The allocation of interrupt vectors to the various
on-chip devices is also a characteristic of the processor HAL.
<filename class="headerfile">proc_intr.h</filename> should be
consulted for appropriate definitions, for example
<varname>CYGNUM_HAL_ISR_UART0</varname>.
      </para>
      <para>
The mask and umask operations are straightforward: if the interrupt
controller has the <literal>SIMR</literal> and <literal>CIMR</literal>
registers those will be used; otherwise the <literal>IRM</literal>
registers will be updated by a read-modify-write cycle. The
acknowledge macro is only relevant for external interrupts coming in
via the edge port module and will clear the interrupt by writing to
the <literal>EPIER</literal> register. There is no simple way to clear
interrupts generated by the on-chip peripherals, so that is the
responsibility of the various device drivers or of application code.
The configure macro is only relevant for external interrupts and
involves manipulating the edge port module.
      </para>
      <para>
The <function>HAL_INTERRUPT_SET_LEVEL</function> macro is used
implicitly by higher level code such as
<function>cyg_interrupt_create</function>. With MCF5282-compatible
interrupt controllers the priority level corresponds to
the <literal>ICRxx</literal> register. The exact format depends on the
processor. Interrupt priorities corresponding to IPL level 7 are
non-maskable. Such interrupts cannot be managed safely by the usual
eCos ISR and DSR mechanisms. Instead application code will have to
install a custom VSR and manage the entire interrupt.
      </para>
      <para>
Some MCF5282-compatible interrupt controllers have a major
restriction: all interrupt priorities within each controller must be
unique. If two interrupts go off at the same time and have exactly the
same priority then the controllers' behaviour is undefined. In a
typical application some of the interrupts will be handled by eCos
device drivers while others will be handled directly by application
code. Since eCos cannot know which interrupts may get used, it cannot
allocate unique priorities. Instead this has to be left to the
application developer. eCos does provide configuration options such as
<varname>CYGNUM_KERNEL_COUNTERS_CLOCK_ISR_PRIORITY</varname> and
<varname>CYGNUM_DEVS_SERIAL_MCFxxxx_SERIAL0_ISR_PRIORITY</varname> to
provide control over the eCos-managed interrupts, and provides default
values for these which are unique.
      </para>
      <caution><para>
Non-unique interrupt priorities can lead to very confusing system
behaviour. For example on an MCF5282, if the PIT3 system clock
(interrupt 0x3a) and ethernet RX frame (interrupt 0x1b) are
accidentally given the same priority and go off at the same time, the
interrupt controller may actually issue an interrupt 0x3b, the bitwise
or of the two interrupt numbers. That interrupt belongs to the on-chip
flash module. There may not be an installed handler for that interrupt
at all, and even if there is a handler it will only manipulate the
flash hardware and not clear the system clock and ethernet interrupts.
Hence the system is likely to go into a spin, continually trying to
service the wrong interrupt. To track down such problems during
debugging it may prove useful to install a breakpoint on the
<function>hal_arch_default_isr</function> function.
      </para></caution>
    </refsect2>

    <refsect2 id="m68k-mcfxxxx-port-clock"><title>Clock Support</title>
      <para>
On processors with an MCF5282-compatible programmable interrupt timer
module or PIT, the variant HAL can provide the
<function>HAL_CLOCK_INITIALIZE</function>,
<function>HAL_CLOCK_RESET</function>,
<function>HAL_CLOCK_READ</function> and
<function>HAL_CLOCK_LATENCY</function> macros. These macros are used
by the eCos kernel to implement the system clock and may be used for
other purposes in non-kernel configurations. When multiple timers are
available it is up to the processor or platform HAL to select which
one gets used for the system clock. It is also up to the processor or
platform HAL to provide various clock-related configuration options
such as <varname>CYGNUM_HAL_RTC_PERIOD</varname>. Those options need
to take into account the processor clock speed, which is usually a
characteristic of the platform and hence not known to the variant HAL.
      </para>
      <para>
When porting to a new Coldfire processor, the processor or platform
HAL should define the symbols
<varname>CYGNUM_HAL_INTERRUPT_RTC</varname>,
<varname>_HAL_MCFxxxx_CLOCK_PIT_BASE_</varname>, and
<varname>_HAL_MCFxxxx_CLOCK_PIT_PRE_</varname>. Existing ports can be
examined for more details.
      </para>
    </refsect2>

    <refsect2 id="m68k-mcfxxxx-port-reset"><title>Reset</title>
      <para>
On processors with an MCF5282-compatible reset module or RST, the
variant HAL can provide the <function>HAL_PLATFORM_RESET</function>
macro. That macro is typically used by the gdb stubs support inside
RedBoot to reset the hardware between debug sessions, ensuring that
each session runs in as close to pristine hardware as possible. The
macro uses the <literal>SOFTRST</literal> bit of the
<varname>RCR</varname> register.
      </para>
    </refsect2>

    <refsect2 id="m68k-mcfxxxx-port-bitindex"><title>Bit Indexing</title>
      <para>
By default the variant HAL will provide versions of
<function>HAL_LSBIT_INDEX</function> and
<function>HAL_MSBIT_INDEX</function> which are more efficient than the
default ones in the architectural HAL. The implementation uses the
<command>ff1.l</command> and <command>bitrev.l</command> instructions.
If the Coldfire processor does not support these instructions then
the processor HAL should define
<varname>_HAL_M68K_MCFxxxx_NO_FF1_</varname>.
      </para>
    </refsect2>

    <refsect2 id="m68k-mcfxxxx-port-other-hal"><title>Other Issues</title>
      <para>
The MCFxxxx variant HAL does not affect the implementation of data
types, stack size definitions, idle thread processing, linker scripts,
SMP support, system startup, or debug support.
      </para>
    </refsect2>

    <refsect2 id="m68k-mcfxxxx-port-other"><title>Other Functionality</title>
      <para>
The MCFxxxx variant HAL only implements functionality defined in the
eCos HAL specification and does not export any additional functions.
      </para>
    </refsect2>
  </refsect1>
</refentry>

</part>
