— eCos Support for the Freescale MCF5282 Processor
The MCF5282 is one member of the Freescale MCFxxxx ColdFire range of
processors. It comes with a number of on-chip peripherals including 3
UARTs and ethernet. The processor HAL package
CYGPKG_HAL_M68K_MCF5282 provides support for
features that are specific to the MCF5282. It complements the M68K
architectural HAL package
CYGPKG_HAL_M68K and the
variant HAL package
eCos configuration should also include a platform HAL package, for
CYGPKG_HAL_M68K_M5282EVB to support
board-level details like the external memory chips.
The MCF5282 processor HAL supports the MCF5280. The only difference between these two processors is the presence of on-chip flash. The platform HAL and the ecos.db target entry will handle this difference.
The MCF5282 processor HAL package should be loaded automatically when eCos is configured for appropriate target hardware. 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 package's CDL script provides default interrupt priorities for some of the mcf5282's on-chip devices. This makes it easier for the various device driver packages to install unique interrupt priorities, as required by the hardware.
The HAL Port
This section describes how the MCF5282 processor HAL package implements parts of the eCos HAL specification. It should be read in conjunction with similar sections from the architectural and variant HAL documentation.
The header file
cyg/hal/proc_io.h provides definitions
of all on-chip peripherals, except for some UART definitions which are
provided by the variant HAL instead. This header file is automatically
included by the architectural header
cyg/hal/hal_io.h, so typically
application code and other packages will just include the latter.
There are default INIT macros for the various on-chip devices which
can be used by platform initialization code, although on any given
platform some of the devices may need special attention.
The MCF5282 reserves a 1-gbyte area of memory for the internal peripheral space. Usually this is mapped between 0x40000000 and 0x7fffffff. Most of this space is not used, but accessing it can cause problems including apparently locking up the processor such that either a hard reset or a watchdog timeout is needed. The target-side gdb stubs code can trap most accesses initiated by host-side gdb, but cannot protect against errant accesses by application code.
It should be noted that the Freescale documentation is occasionally confusing when it comes to numbering devices. For example the four on-chip programmable timers are numbered PIT1 to PIT4, but in the interrupt controller the corresponding interrupts are numbered PIT0 to PIT3. The eCos port consistently starts numbering at 0, so the timers have been renamed PIT0 to PIT3.
The header file
cyg/hal/proc_intr.h provides VSR and ISR
vector numbers for all interrupt sources. The VSR vector number, for
CYGNUM_HAL_VECTOR_TMR0, should be used
for calls like
corresponds directly to the M68K exception number. The ISR vector
number, for example
CYGNUM_HAL_ISR_TMR0, should be
used for calls like
header file is automatically included by the architectural header
cyg/hal/hal_intr.h, and other
packages and application code will normally just include the latter.
The eCos HAL macros
HAL_INTERRUPT_CONFIGURE are implemented by the
processor HAL. The mask and unmask operations are straightforward,
simply manipulating the IMR registers in the on-chip interrupt
controllers. The acknowledge macro is only relevant for external
interrupts coming in via the edge port module and will clear the
interrupt by writing to the EPIER register. There is no simple way to
clear interrupts generated by other sources. Instead each such
interrupt has to be cleared in a device-specific way, and that is the
responsibility of the appropriate device driver. The configure macro
is only relevant for external interrupts and involves manipulating the
edge port module.
HAL_INTERRUPT_SET_LEVEL macro, used
implicitly by higher level code such as
cyg_interrupt_create, is also implemented by the
processor HAL. In the MCF5282 processor interrupt priorities have to
be managed very carefully. Interrupts are managed via two interrupt
controllers, INTC0 and INTC1. Each controller contains ICRxx control
registers for each interrupt to manage that interrupt's priority. The
HAL_INTERRUPT_SET_LEVEL macro simply fills in the
An ICRxx value is a six-bit number. The top three bits correspond to
the standard M68K IPL interrupt level. The bottom three bits give a
finer-grained priority within that IPL level. For example, if the
priority argument to
cyg_interrupt_create is 42
then that corresponds to an IPL level of 5 and a finer-grained
priority of 2. If the system has been configured to support nested
interrupts and a level 42 interrupt goes off, the processor's IPL
level will be set to 5 so all interrupts with priorities < 48
will remain blocked. The finer-grained priority controls what happens
when two interrupts with the same IPL level go off at the same time.
Interrupt priorities between 0 and 7 would correspond to an IPL level of 0. The interrupt controller can only raise an interrupt if the IPL level is at least 1, so the smallest valid interrupt priority is 8. Interrupt priorities between 56 and 63 correspond to IPL level 7, and such interrupts are non-maskable and must be used with care. These interrupts cannot be managed safely by the usual eCos ISR and DSR mechanisms, instead application code will have to install a custom VSR and manage the entire interrupt. This means that interrupt priorities should normally be in the range 8 to 55.
As a special case, external interrupts coming in via the edge port
module have hard-wired priorities which do not clash with the
programmable ones. For these the priority argument to
HAL_INTERRUPT_SET_LEVEL and higher-level code is
The MCF5282 interrupt controllers have a major restriction: all
interrupt priorities within each controller must be unique. If two
interrupts go off at the same time and have exactly the same priority
then the controllers' behaviour is undefined. In a typical application
some of the interrupts will be handled by eCos device drivers while
others will be handled directly by application code. Since eCos cannot
know which interrupts may get used, it cannot allocate unique
priorities. Instead this has to be left to the application developer.
eCos does provide configuration options such as
provide control over the eCos-managed interrupts, and provides default
values for these which are unique.
To ensure that the configured interrupt priorities are unique the
processor HAL comes with a test case
source code for this can be found in the package's
tests subdirectory. The test examines the
ICRxx registers in both interrupt controllers. It will report all
priorities that are in use, and report a failure if a non-unique
priority is detected. This code may prove useful for application
developers trying to allocate interrupt priorities.
Non-unique interrupt priorities can lead to very confusing system
behaviour. For example if the PIT3 system clock (interrupt 0x3a) and
ethernet RX frame (interrupt 0x1b) are accidentally given the same
priority and go off at the same time, the interrupt controller may
actually issue an interrupt 0x3b, the bitwise or of the two interrupt
numbers. That interrupt belongs to the on-chip flash module. There may
not be an installed handler for that interrupt at all, and even if
there is a handler it will only manipulate the flash hardware and not
clear the system clock and ethernet interrupts. Hence the system is
likely to go into a spin, continually trying to service the wrong
interrupt. To track down such problems during debugging it may prove
useful to install a breakpoint on the
The processor HAL provides support for the eCos system clock. This always uses hardware timer PIT3, which should not be manipulated directly by application code. If gprof-based profiling is enabled then that will use hardware timer PIT2. PIT timers 0 and 1 are never used by eCos so application code is free to manipulate these as required.
Some of the configuration options related to the system clock, for
CYGNUM_HAL_RTC_PERIOD, are actually
contained in the platform HAL rather than the processor HAL. These
options need to take into account the processor clock speed, a
characteristic of the platform rather than the processor.
The MCF5282 has 2K of cache. Usually this will be set up as a split cache, 1K for instructions and 1K for data, which should give the best performance for typical applications. The standard HAL cache macros are supported.
On some platforms it may be better to organize the cache differently.
For example if the platform involves running code only out of internal
flash but may access external data, it may be possible to improve
performance by using a 2K data cache instead of a split cache. This is
which may be either a fixed
#define or a
configuration option depending on the platform. For more details see
the header file
The MCF5282 processor HAL does not affect the implementation of data types, stack size definitions, bit indexing, idle thread processing, linker scripts, SMP support, system startup, or debug support.
The MCF5282 processor HAL only implements functionality defined in the eCos HAL specification and does not export any additional functions.
|2022-09-14||eCosPro Non-Commercial Public License|