eCos Support for the Freescale M5272C3 Board — Overview
The Freescale M5272C3 board has an MCF5272 ColdFire processor, 4MB of external SDRAM, 2MB of external flash memory, and connectors plus required support chips for all the on-chip peripherals. By default the board comes with its own dBUG ROM monitor, located in the bottom half of the flash.
For typical eCos development a RedBoot image is programmed into the top half of the flash memory, and the board is made to boot this image rather than 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.
In a typical setup the bottom half of the flash memory is reserved for the dBUG ROM monitor and is not accessible to eCos. That leaves four flash blocks of 256K each. Of these one is used for the RedBoot image and another is used for managing the flash and holding RedBoot fconfig values. The remaining two blocks at 0xFFF40000 and 0xFFF80000 can be used by application code.
By default eCos will only support the four megabytes of external SDRAM
present on the initial versions of the board, accessible at location
0x00000000. Later versions come with 16MB. If all 16MB of memory are
required then the ACR0 register needs to be changed. The default value
is controlled by the configuration option
CYGNUM_HAL_M68K_M5272C3_ACR0, but this option is
only used during ROM startup so in a typical setup it would be
necessary to rebuild and update RedBoot. Alternatively the register
can be updated by application code, preferably using a high priority
static constructor to ensure that the extra memory is visible before
any code tries to use that memory. It will also be necessary to change
the memory layout so that the linker knows about the additional
By default the 4K of internal SRAM is mapped to location 0x20000000
using the RAMBAR register. This is not used by eCos or by RedBoot so
can be used by application code. The M68K architectural HAL has an
iram1.c testcase to illustrate the linker script
support for this. The internal 16K of ROM is left
disabled by default because its contents are of no use to most
applications. The on-chip peripherals are mapped at 0x10000000 via the
There is a serial driver
which supports both on-chip UARTs. One of the UARTs, usually uart0,
can be used by RedBoot for communication with the host. If this UART
is needed by the application, either directly or via the serial
driver, then it cannot also be used for RedBoot communication. Another
communication channel such as ethernet should be used instead. The
serial driver package is loaded automatically when configuring for the
There is an ethernet driver
for the on-chip ethernet device. This driver is also loaded
automatically when configuring for the M5272C3 target. The M5272C3
board does not have a unique MAC address, so a suitable address has to
be programmed into flash via RedBoot's fconfig
eCos manages the on-chip interrupt controller. Timer 3 is used to implement the eCos system clock, but timers 0, 1 and 2 are unused and left for the application. The GPIO pins are manipulated only as needed to get the UARTs and ethernet working. eCos will reset the remaining on-chip peripherals (DMA, USB, PLCI, QSPI and PWM) during system startup or soft reset but will not otherwise manipulate them.
The M5272C3 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.
|2021-09-02||Open Publication License|