eCos Support for the Freescale M5282LITE Board — Overview
The Freescale M5282LITE board has an MCF5282 ColdFire processor, 16MB of external SDRAM, 2MB of external flash memory, and connectors plus required support chips for the on-chip peripherals. By default the board comes with its own dBUG ROM monitor located in the external flash.
For typical eCos development a RedBoot image is programmed into the external flash replacing the existing dBUG monitor. RedBoot provides gdb stub functionality so it is then possible to download and debug eCos applications via the gdb debugger. This can happen over either a serial line or over ethernet.
The memory map used by both eCos and RedBoot is as follows:
eCos can be configured for one of three startup types:
This is the startup type normally used during application development. RedBoot is programmed into flash and performs the initial bootstrap. m68k-elf-gdb is then used to load a RAM startup application into memory and debug it. By default the application will use eCos' virtual vectors mechanism to obtain certain services from RedBoot, including diagnostic output.
With a minor change to the eCos configuration this startup type can also be used to debug applications via BDM.
- 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. 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. It is used primarily for building a special version of RedBoot, used during hardware setup.
- This startup type can be used for finished applications which will be programmed into flash at location 0xFFE00000. The application will be self-contained with no dependencies on services provided by other software. eCos startup code will perform all necessary hardware initialization. This startup type is used for building the flash-resident version of RedBoot but can also be used for application code.
For all startup types the external SDRAM is used to hold all data. For RAM and dBUG startup the code also resides in external SDRAM, with the first 64K reserved for use by the ROM monitor. The 64K of internal RAM is not used, either by RedBoot or by eCos, so all of it is available to the application. The 512K of internal flash is not currently used.
In a typical setup the first two 64K flash blocks are used for holding the RedBoot image, and the last block is used for managing the flash and holding the RedBoot fconfig values. The remaining 29 blocks from 0xFFE20000 to 0xFFFEFFFF can be used by application code.
RedBoot can communicate with the host using either ethernet or one of the UARTs - usually uart0 corresponding to the existing serial connector on the M5282LITE board.
All configurations for the M5282LITE target include an ethernet driver
CYGPKG_DEVS_ETH_MCFxxxx. If the application
does not actually require ethernet functionality then the package is
inactive and the final executable will not suffer any overheads from
unused functionality. This is determined by the presence of the
generic ethernet I/O package
Typically the choice of eCos template causes the right thing to
happen. For example the default template does not include any TCP/IP
CYGPKG_IO_ETH_DRIVERS is not included, but
both the net and redboot templates do include a TCP/IP stack so will
specify that package and hence enable the ethernet driver. The
ethernet device can be shared by RedBoot and the application, so it is
possible to debug a networked application over ethernet.
The M5282LITE board does not have a serial EPROM or similar hardware providing a unique network MAC address. Instead a suitable address has to be programmed into flash via RedBoot's fconfig command.
All configurations for the M5282LITE target include a serial device
driver as a whole is inactive unless the generic serial support,
CYGPKG_IO_SERIAL_DEVICES is enabled. Exactly which
of the on-chip UARTs are supported is controlled by configuration
options within the platform HAL. By default only uart0 is supported
since on the standard board that is the only one with a connector. If
the UART is needed by the application then it cannot also be used by
RedBoot for gdb traffic, so another communication channel such as
ethernet should be used instead.
All configurations for the M5282LITE target also include a watchdog
driver is inactive unless the generic watchdog support
CYGPKG_IO_WATCHDOG is loaded.
The on-chip interrupt controllers and the edge port module are managed by eCos using macros provided by the MCF5282 processor HAL. PIT timer 3 is normally used to implement the eCos system clock. If gprof-based profiling is enabled then that will use PIT timer 2. PIT timers 0 and 1 are unused and can be manipulated by the application. The GPIO pins are manipulated only as needed to get the UART(s) and ethernet working. eCos will reset the remaining on-chip peripherals (DMA, GPT, DMA timers, QSPI, I²C, FlexCAN, and QADC) during system startup or soft reset, but will not otherwise manipulate them.
The M5282LITE port is intended to work with GNU tools configured for an m68k-elf target. The original port was done using m68k-elf-gcc version 3.2.1, m68k-elf-gdb version 5.3, and binutils version 2.13.1.
By default eCos is built using the compiler flag
-fomit-frame-pointer. Omitting the frame pointer
eliminates some work on every function call and makes another register
available, so the code should be smaller and faster. However without a
frame pointer m68k-elf-gdb is not always able to identify stack
frames, so it may be unable to provide accurate backtrace information.
Removing this compiler flag from the configuration option
CYGBLD_GLOBAL_CFLAGS avoids such debug problems.
A typical setup involves m68k-elf-gdb
interacting with RedBoot using either serial or ethernet.
Alternatively it is possible to debug via the BDM port. The package's
misc subdirectory contains a
bdm.gdb that contains macros for the
low-level hardware initialization normally performed by the ROM
startup code. The application should be linked with an eCos
configuration using RAM startup, and with the options
CYGSEM_HAL_USE_ROM_MONITOR disabled to stop eCos
accessing any services provided by RedBoot. Diagnostic output will be
sent out of uart0.
|2021-09-02||eCosPro Non-Commercial Public License|