The HAL Port
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HAL Port — Implementation Details

Overview

This documentation explains how the eCos HAL specification has been mapped onto the SDK7780 hardware, and should be read in conjunction with that specification. The SDK7780 platform HAL package complements the SH architectural HAL and the SH4 variant HAL. It provides functionality which is specific to the target board.

Startup

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 SDRAM and programming the various internal registers including clocks, EMI and LMI. The values used for most of these registers are assigned fixed values from a table in the header cyg/hal/platform.inc.

Linker Scripts and Memory Maps

The platform HAL package provides the memory layout information needed to generate the linker script. The key memory locations are as follows:

off-chip Flash
This is located at address 0x00000000 of the physical memory space and is therefore accessible in the P1 region at location 0x80000000. An uncached shadow of this memory is available in the P2 region at 0xA0000000. The contents of the flash are organized as described earlier.
external SDRAM
This is located at address 0x08000000 of the physical memory space and is therefore accessable in the P1 region at location 0x88000000. An uncached shadow of this memory is available in the P2 region at 0xA8000000. The first 512 bytes are used for hardware exception vectors. The next 256 bytes are normally used for the eCos virtual vectors, allowing RAM-based applications to use services provided by the ROM monitor. For ROM startup, all remaining SDRAM is available. For RAM startup, available SDRAM starts at location 0x88020000, with the bottom 128Kbytes reserved for use by RedBoot.
on-chip peripherals
These are accessible via the P4 region at location 0xE0000000 onwards. The on-chip PCI controller has apertures into the PCI memory bus at 0xB0000000 and 0xFD000000 in the P2 region, and access to to the PCI IO space at 0xFE200000. Other base addresses of on-chip peripherals can be found in the SH7780 Hardware Manual.
off-chip peripherals
All off-chip peripherals used by eCos are accessed via on-chip bus controllers such as LMI or PCI. All others are left untouched.

Clock Support

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. Timers 2 to 5 are not used by eCos so application code is free to manipulate these 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 (resulting visibly in garbage on the serial output).

The SH7780 extends the SH family clock model by providing a CLOCKGEN subsystem allowing the hardware clock frequency to be controlled. The CLOCKGENA.PLL1CR register is the primary means to do this, and is initialised by switches 1, 2, 3 and 7 on DIP switch block MD_SW. The delivery default settings for these switches is to select clock mode 0 giving a 400MHz CPU clock, 100MHz local bus and 50MHz peripheral clock.

If the DIP switches are changed from the default then the values of CYGHWR_HAL_SH_OOC_DIVIDER_IFC, CYGHWR_HAL_SH_OOC_DIVIDER_BFC and CYGHWR_HAL_SH_OOC_DIVIDER_PFC must be changed to match.

Other Issues

The SDK7780 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.

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