Configuration — Platform-specific Configuration Options
The M5282EVB platform HAL package is loaded automatically when eCos is configured for an M5282EVB 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.
The M5282EVB platform HAL package supports four separate startup
types, controlled by the configuration option
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.
m68k-elf-gdb 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, but that can be
- This startup type can be used for finished applications which boot directly from 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. The flash-resident version of RedBoot uses this startup type.
- 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.
- 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.
RedBoot and Virtual Vectors
If the application is intended to act as a ROM monitor, providing
services for other applications, then the configuration option
CYGSEM_HAL_ROM_MONITOR should be set. Typically
this option is set only when building RedBoot.
If the application is supposed to make use of services provided by a
ROM monitor, via the eCos virtual vector mechanism, then the
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. That is useful as a
testing step before switching to ROM startup. It also allows
applications to be run and debugged via BDM.
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
CYGHWR_HAL_M68K_M5282EVB_DIAGNOSTICS_PORT. The baud
rate for the selected port is controlled by
The platform HAL package contains flash driver support for the
external flash. By default this is inactive, and it can be made active
by loading the generic flash package
The MCF5282 processor has a number of special registers controlling
the cache, on-chip RAM and flash, and so on. The platform HAL provides a
number of configuration options for setting these, for example
CYGNUM_HAL_M68K_M5282EVB_RAMBAR controls the initial
value of the RAMBAR register.
By default the system clock interrupts once every 10ms, corresponding
to a 100Hz clock. This can be changed by the configuration option
CYGNUM_HAL_RTC_PERIOD, the number of microseconds
between clock ticks. Other clock-related settings are recalculated
automatically if the period is changed.
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:
The m68k-elf-gcc compiler supports many
variants of the M68K architecture, from the original 68000 onwards.
-moption should be used to select the specific variant in use, and with current tools
-m5200is the closest match for an MCF5282 processor.
- This option forces m68k-elf-gcc 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.
%A6register 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 m68k-elf-gdb debugger is not always able to interpret a thread stack, so it cannot reliably give a backtrace. Removing
-fomit-frame-pointerfrom the default flags will make debugging easier, but the generated code may be worse.
|2021-09-02||eCosPro Non-Commercial Public License|