m68k-m5272c3-config.html
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><H1
><A
NAME="M68K-M5272C3-CONFIG"
></A
>Configuration</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN19499"
></A
><H2
>Name</H2
>Configuration -- Platform-specific Configuration Options</DIV
><DIV
CLASS="REFSECT1"
><A
NAME="M68K-M5272C3-CONFIG-OVERVIEW"
></A
><H2
>Overview</H2
><P
>The M5272C3 platform HAL package is loaded automatically when eCos is
configured for an M5272C3 target. It should never be necessary to load
this package explicitly. Unloading the package should only happen as a
side effect of switching target hardware.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="M68K-M5272C3-CONFIG-STARTUP"
></A
><H2
>Startup</H2
><P
>The M5272C3 platform HAL package supports four separate startup types:
</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
>RAM</DT
><DD
><P
>This is the startup type which is normally used during application
development. The board has RedBoot programmed into flash at location
0xFFF00000 and boots from that location.
<SPAN
CLASS="APPLICATION"
>m68k-elf-gdb</SPAN
> is then used to load a RAM
startup application into memory and debug it. It is assumed that the
hardware has already been initialized by RedBoot. By default the
application will use eCos' virtual vectors mechanism to obtain certain
services from RedBoot, including diagnostic output.
</P
></DD
><DT
>ROM</DT
><DD
><P
>This startup type can be used for finished applications which will
be programmed into flash at location 0xFFF00000. The application will
be self-contained with no dependencies on services provided by other
software. eCos startup code will perform all necessary hardware
initialization.
</P
></DD
><DT
>ROMFFE</DT
><DD
><P
>This is a variant of the ROM startup type which can be used if the
application will be programmed into flash at location 0xFFE00000,
overwriting the board's dBUG ROM monitor.
</P
></DD
><DT
>DBUG</DT
><DD
><P
>This is a variant of the RAM startup which allows applications to be
loaded via the board's dBUG ROM monitor rather than via RedBoot. It
exists mainly to support the dBUG version of RedBoot which is needed
during hardware setup. Once the application has started it will take
over all the hardware, and it will not depend on any services provided
by dBUG. This startup type does not provide gdb debug facilities.
</P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="M68K-M5272C3-CONFIG-REDBOOT"
></A
><H2
>RedBoot and Virtual Vectors</H2
><P
>If the application is intended to act as a ROM monitor, providing
services for other applications, then the configuration option
<CODE
CLASS="VARNAME"
>CYGSEM_HAL_ROM_MONITOR</CODE
> should be set. Typically
this option is set only when building RedBoot.
</P
><P
>If the application is supposed to make use of services provided by a
ROM monitor, via the eCos virtual vector mechanism, then the
configuration option <CODE
CLASS="VARNAME"
>CYGSEM_HAL_USE_ROM_MONITOR</CODE
>
should be set. By default this option is enabled when building for a
RAM startup, disabled otherwise. It can be manually disabled for a RAM
startup, making the application self-contained, as a testing step
before switching to ROM startup.
</P
><P
>If the application does not rely on a ROM monitor for diagnostic
services then one of the serial ports will be claimed for HAL
diagnostics. By default eCos will use the terminal port, corresponding
to uart0. The auxiliary port, uart1, can be selected instead via the
configuration option
<CODE
CLASS="VARNAME"
>CYGHWR_HAL_M68K_MCFxxxx_DIAGNOSTICS_PORT</CODE
>. The baud
rate for the selected port is controlled by
<CODE
CLASS="VARNAME"
>CYGNUM_HAL_M68K_MCFxxxx_DIAGNOSTICS_BAUD</CODE
>.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="M68K-M5272C3-CONFIG-FLASH"
></A
><H2
>Flash Driver</H2
><P
>The platform HAL package contains flash driver support. By default
this is inactive, and it can be made active by loading the generic
flash package <CODE
CLASS="VARNAME"
>CYGPKG_IO_FLASH</CODE
>.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="M68K-M5272C3-CONFIG-REGISTERS"
></A
><H2
>Special Registers</H2
><P
>The MCF5272 processor has a number of special registers controlling
the cache, on-chip RAM and ROM, and so on. The platform HAL provides a
number of configuration options for setting these, for example
<CODE
CLASS="VARNAME"
>CYGNUM_HAL_M68K_M5272C3_RAMBAR</CODE
> controls the initial
value of the RAMBAR register. These options are only used during a ROM
or ROMFFE startup. For a RAM startup it will be RedBoot that
initializes these registers, so if the default values are not
appropriate for the target application then it will be necessary to
rebuild RedBoot with new settings for these options. Alternatively it
should be possible to reprogram some or all of the registers early on
during startup, for example by using a high-priority static
constructor.
</P
><P
>One of the special registers, MBAR, cannot be controlled via a
configuration option. Changing the value of this register could have
drastic effects on the system, for example moving the on-chip
peripherals to a different location in memory, and it would be very
easy to end up with inconsistencies between RedBoot and the eCos
application. Instead the on-chip peripherals are always mapped to
location 0x10000000.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="M68K-M5272C3-CONFIG-CLOCK"
></A
><H2
>System Clock</H2
><P
>By default the system clock interrupts once every 10ms, corresponding
to a 100Hz clock. This can be changed by the configuration option
<CODE
CLASS="VARNAME"
>CYGNUM_HAL_RTC_PERIOD</CODE
>, the number of microseconds
between clock ticks. Other clock-related settings are recalculated
automatically if the period is changed.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="M68K-M5272C3-CONFIG-FLAGS"
></A
><H2
>Compiler Flags</H2
><P
>The platform HAL defines the default compiler and linker flags for all
packages, although it is possible to override these on a per-package
basis. Most of the flags used are the same as for other architectures
supported by eCos. There are three flags specific to this port:
</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><CODE
CLASS="OPTION"
>-mcpu=5272</CODE
></DT
><DD
><P
>The <SPAN
CLASS="APPLICATION"
>m68k-elf-gcc</SPAN
> compiler supports many
variants of the M68K architecture, from the original 68000 onwards.
For an MCF5272 processor <CODE
CLASS="OPTION"
>-mcpu=5272</CODE
> should be used.
</P
></DD
><DT
><CODE
CLASS="OPTION"
>-malign-int</CODE
></DT
><DD
><P
>This option forces <SPAN
CLASS="APPLICATION"
>m68k-elf-gcc</SPAN
> to align
integer and floating point data to a 32-bit boundary rather than a
16-bit boundary. It should improve performance. However the resulting
code is incompatible with most published application binary interface
specifications for M68K processors, so it is possible that this option
causes problems with existing third-party object code.
</P
></DD
><DT
><CODE
CLASS="OPTION"
>-fomit-frame-pointer</CODE
></DT
><DD
><P
>Traditionally the <CODE
CLASS="VARNAME"
>%A6</CODE
> register was used as a
dedicated frame pointer, and the compiler was expected to generate
link and unlink instructions on procedure entry and exit. These days
the compiler is perfectly capable of generating working code without a
frame pointer, so omitting the frame pointer often saves some work
during procedure entry and exit and makes another register available
for optimization. However without a frame pointer register the
<SPAN
CLASS="APPLICATION"
>m68k-elf-gdb</SPAN
> debugger is not always able to
interpret a thread stack, so it cannot reliably give a backtrace.
Removing <CODE
CLASS="OPTION"
>-fomit-frame-pointer</CODE
> from the default flags
will make debugging easier, but the generated code may be worse.
</P
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