Configuration — Platform-specific Configuration Options


The DNP/5280 platform HAL package is loaded automatically when eCos is configured for a dnp5280, dnp5280_v12 or dnp5282 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 DNP/5280 platform HAL package supports three separate startup types: RAM, DBUG, and ROM. The configuration option CYG_HAL_STARTUP controls which startup type is being used. For typical application development RAM startup should be used, and the application will be run via m68k-elf-gdb interacting with RedBoot using either serial or ethernet. It is assumed that the low-level hardware initialization, including setting up the memory map, has already been performed by RedBoot. By default the application will use certain services provided by RedBoot via the virtual vector mechanism, including diagnostic output, but that can be disabled via CYGSEM_HAL_USE_ROM_MONITOR.

ROM startup can be used for applications which boot directly from flash. All the hardware will be initialized, and the application is self-contained. This startup type is used by the flash-resident version of RedBoot, and can also be used for finished applications.

DBUG startup can be used for applications which will be loaded via the DBUG ROM monitor rather than RedBoot. As with RAM startup it is assumed that the memory map has already been set up, but the application will not use any services provided by the ROM monitor.

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 configuration option CYGSEM_HAL_USE_ROM_MONITOR 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 uart0. If the actual hardware has connectors for uart1 or uart2, one of these can be selected instead via the configuration option CYGHWR_HAL_M68K_MCFxxxx_DIAGNOSTICS_PORT. The baud rate for the selected port is controlled by CYGNUM_HAL_M68K_MCFxxxx_DIAGNOSTICS_BAUD.

Optional Hardware

The platform HAL assumes that a DNP/5280 module is plugged into a standard DNP/EVA2_SV6 carrier board, and that a DNP/5282 module is plugged into a DNP/EVA6. This can be changed via the configuration option CYGHWR_HAL_M68K_MCF528x_HARDWARE_DNP528x_BOARD. The choice of carrier board determines the default settings of the various GPIO pins, in other words which pins are connected to on-chip peripherals. For example an EVA2_SV6 board only has a single uart transceiver and connector so only uart0's signals are connected to the appropriate pins. An EVA6 has two transceivers and connectors so both uart0 and uart1 are connected. When using a non-standard carrier board it is possible to define the pin connectivity via configuration options in the CDL component CYGHWR_HAL_M68K_MCF528x_GPIO. The configuration should adjust accordingly, enabling or disabling devices as appropriate. Mostly this happens in the MCF5282 processor HAL and the MCFxxxx variant HAL.

Special Registers

The MCF5282 processor has a number of special registers controlling the cache, on-chip RAM, and so on. The platform HAL provides a number of configuration options for setting these, for example CYGNUM_HAL_M68K_DNP5280_RAMBAR controls the initial value of the RAMBAR register.

System Clock

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.

Compiler Flags

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. A -m option should be used to select the specific variant in use, and with current tools -m5200 is 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.
Traditionally the %A6 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 m68k-elf-gdb debugger is not always able to interpret a thread stack, so it cannot reliably give a backtrace. Removing -fomit-frame-pointer from the default flags will make debugging easier, but the generated code may be worse.