HAL Port — Implementation Details
This documentation explains how the eCos HAL specification has been mapped onto the MicroDev hardware, and should be read in conjunction with that specification. The MicroDev platform HAL package complements the SH architectural HAL and the SH4 variant HAL. It provides functionality which is specific to the target board.
Following a hard or soft reset the HAL will initialize or reinitialize most of the on-chip peripherals. There is an exception for RAM startup applications which depend on a ROM monitor for certain services.
For ROM startup, the HAL will perform additional initialization,
setting up the external DRAM and programming the various internal
registers. The values used for most of these registers are assigned
fixed values from a table in the header
The platform HAL provides configuration options for the eCos system clock. This always uses the hardware timer 0, which should not be used directly by application code. Timer 1 is used to implement a microsecond resolution busy delay service. Timer 2 is not used by eCos so application code is free to manipulate this as required. The actual HAL macros for managing the clock are provided by the SH architecture processor HAL.
There is a software model of the structure of the SH family clock
supply subsystem which performs the correct calculations to yield not
only the inputs for the CPU clock but also the peripheral clocks fed
to the serial device, memory controllers and other devices. The values
for the master crystal, the PLL multipliers and various dividers are
supplied by the platform HAL. Some care must be taken in defining
these since wrong values will cause the timers and the SCIF baud rate
to be miscalculated. If the OSCAR chip switches are changed from the
default then the value of
must be changed to match.
The MicroDev platform HAL does not affect the implementation of other parts of the eCos HAL specification. The SH4 variant HAL, and the SH architectural HAL documentation should be consulted for further details.
It should be noted that the floating point support in the SH HAL has a
caveat that, if the FPSCR register is changed, it may get reverted at a
later stage by certain operations performed by the GCC compiler. This
behaviour is intentional as the alternative would be to update the GCC
compiler's internal state about the FPSCR at every context switch which
would be expensive for a feature that is unlikely to be used frequently.
If the FPSCR is to be changed by the application, the developer
should call the function
__set_fpscr(int), passing it
the new FPSCR value.
|2023-08-15||Open Publication License|