The HAL Port

Name

HAL Port -- Implementation Details

Overview

This section covers any remaining items of note related to the STR7xx variant support, not covered in previous sections.

LEDs

If a platform port has support for the display of values on LEDs, that support is standardised to be accessible from C with the following function:

#include <cyg/infra/hal_diag.h>
extern void hal_diag_led(int leds);

Clock Control

The platform HAL must provide the input clock frequency (CYGARC_HAL_STR7XX_INPUT_CLOCK) in its CDL file.

STR7XX definitions

The STR7XX variant HAL port includes the header file var_io.h which provides useful register definitions used by eCos, that can also be freely used by applications. It includes only limited register definitions for subsystems unused by eCos.

It may be found in the include/cyg/hal directory relative to your configuration's install tree, or alternatively in the source repository at hal/arm/str7xx/var/VERSION/include/var_io.h. However it should be properly included by applications by using:

#include <cyg/hal/hal_io.h>
to allow for platform HALs to augment or override any relevant definitions.

Power Control

The kernel idle thread is scheduled to run when the system has no other tasks able to run. The idle thread can call a HAL supplied macro to place the chip into an appropriate power saving mode instead of just going around a busy loop. The STR7XX variant HAL defines the HAL_IDLE_THREAD_ACTION macro to use the STR7XX power control support to place the chip into WFI mode which will stop the processor clock, without disabling the on-chip peripherals. This state continues until an interrupt is received.

Further power saving can be achieved by reducing the system clock frequencies using hal_str7xx_clocks_setup() described above. This function only changes the clock frequencies; it may also be necessary to change the values of dividers in various peripherals to compensate. There are several routines supplied in the HAL to do this.

Calling hal_str7xx_uart_reinit() will cause all the UART baud rate dividers to be reset to match the current value of PCLK1. Note that there are limitations to the range of baud rates that can be set, PCLK1 must be at least 16 times the required rate. Also, the resolution of the baud rate divider may make certain baud rates less accurate at different PCLK1 frequencies.

Calling hal_str7xx_watchdog_init(CYGNUM_DEVS_WATCHDOG_ARM_STR7XX_DESIRED_TIMEOUT_US) will cause the watchdog to be reinitialized with a timeout based on the current value of PCLK2. The resolution of the prescaler and the size of the 16 bit counter may render certain watchdog timeouts unachievable at some clock rates.

Calling HAL_CLOCK_INITIALIZE(CYGNUM_HAL_RTC_PERIOD) will cause the main system timer to be reinitialized based on the current value of PCLK2.

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