Configuration

Name

Configuration -- Platform-specific Configuration Options

Overview

The AT91SAM7S-EK platform HAL package is loaded automatically when eCos is configured for the at91sam7sek target. It should never be necessary to load this package explicitly. Unloading the package should only happen as a side effect of switching target hardware.

Startup

The platform HAL package supports three separate startup types:

RAM

This is the startup type which is normally used during application development. The board has GDB stubs programmed into flash and boots into that initially. arm-eabi-gdb is then used to load a RAM startup application into memory and debug it. It is assumed that the hardware has already been initialized by the stubs. By default the application will use the eCos virtual vectors mechanism to obtain certain services from the stubs, including diagnostic output.

ROM

This startup type can be used for finished applications which will be programmed into flash at physical address 0x00100000. The application will be self-contained with no dependencies on services provided by other software. eCos startup code will perform all necessary hardware initialization.

JTAG

This is an alternative development startup type. The application is loaded into RAM via a JTAG device and is run and debugged from there. The application will be self-contained with no dependencies on services provided by other software. It is expected that hardware setup will have been performed via the JTAG device prior to loading.

GDB Stubs and Virtual Vectors

If the application is intended to act as a ROM monitor, providing services for other applications, then the configuration option CYGSEM_HAL_ROM_MONITOR should be set. Typically this option is set only when building the GDB Stubs.

If the application is supposed to make use of services provided by a ROM monitor, via the eCos virtual vector mechanism, then the configuration option CYGSEM_HAL_USE_ROM_MONITOR should be set. By default this option is enabled when building for a RAM startup, disabled otherwise. It can be manually disabled for a RAM startup, making the application self-contained, as a testing step before switching to ROM startup.

If the application does not rely on a ROM monitor for diagnostic services then the serial port will be claimed for HAL diagnostics.

Flash Driver

The AT91SAM7S-EK board contains a quantity of on-chip flash memory. The CYGPKG_DEVS_FLASH_AT91 package contains all the code and data definitions necessary to support this part. This driver is not active until the generic Flash support package, CYGPKG_IO_FLASH, is included in the configuration.

Watchdog Driver

The AT91SAM7S-EK board use the AT91SAM7S's internal watchdog support. The CYGPKG_DEVICES_WATCHDOG_ARM_AT91WDTC package contains all the code necessary to support this device. Within that package the CYGNUM_DEVS_WATCHDOG_ARM_AT91WDTC_DESIRED_TIMEOUT_MS configuration option controls the watchdog timeout, and by default will force a reset of the board upon timeout. This driver is not active until the generic watchdog device support package, CYGPKG_IO_WATCHDOG, is included in the configuration.

Note that on the AT91, the on-chip watchdog peripheral always starts running immediately, and so in configurations that do not include the watchdog driver, it is always disabled via its write-once register. In configurations which include the watchdog driver obviously the watchdog is not disabled otherwise it could not be subsequently re-enabled, and so the application must start and periodically reset the watchdog from the very beginning of execution.

USART Serial Driver

The AT91SAM7S-EK board use the AT91SAM7S's internal USART serial support as described in the AT91 processor HAL documentation. Two serial ports are available: the serial debug port which is mapped to virtual vector channel 0 in the HAL diagnostic driver or "/dev/dbg" in the interrupt-driven driver; and USART 0 which is mapped to virtual vector channel 1 and "/dev/ser0". Only USART 0 supports modem control signals such as those used for hardware flow control.

Compiler Flags

The SAM7 variant HAL defines the default compiler and linker flags for all packages, although it is possible to override these on a per-package basis. Most of the flags used are the same as for other architectures supported by eCos. There are just three flags specific to this port:

-mcpu=arm7tdmi

The arm-eabi-gcc compiler supports many variants of the ARM architecture. A -m option should be used to select the specific variant in use, and with current tools -mcpu=arm7tdmi is the correct option for the ARM7TDMI processor in the SAM7S.

-mthumb

The arm-eabi-gcc compiler will compile C and C++ files into the Thumb instruction set when this option is used. The best way to build eCos in Thumb mode is to enable the configuration option CYGHWR_THUMB.

-mthumb-interwork

This option allows programs to be created that mix ARM and Thumb instruction sets. Without this option, some memory can be saved. This option should be used if -mthumb is used. The best way to build eCos with Thumb interworking is to enable the configuration option CYGBLD_ARM_ENABLE_THUMB_INTERWORK.

2017-02-09
Documentation license for this page: eCosPro License