On-chip Subsystems and Peripherals — Hardware Support
The ST LM3S parts include on-chip SRAM, and on-chip FLASH. The RAM consists of up to 64KiB and the FLASH can be up to 512KiB in size depending on model.
Typically, an eCos platform HAL port will expect a GDB stub ROM monitor to be programmed into the LM3S on-chip ROM memory for development, and the board would boot this image from reset. The stub ROM provides GDB stub functionality so it is then possible to download and debug stand-alone and eCos applications via the gdb debugger using serial interfaces or other debug channels. The JTAG interface may also be used for development if a suitable JTAG device is available. For production purposes, applications are programmed into external or on-chip FLASH and will be self-booting.
CYGPKG_DEVS_FLASH_LM3S provides a
driver for the on-chip flash. This driver conforms to the Version
2 flash driver API. It queries the microcontroller's device
capabilities registers to determine the size and layout of the
flash at runtime.
The LM3S does not contain any caches, however, the variant HAL
cyg/hal/hal_cache.h header to
satisfy generic code. This header describes zero sized caches and
provides null macros for the required functions.
The LM3S variant HAL supports basic polled HAL diagnostic I/O
over any of the on-chip serial devices. There is also a fully
interrupt-driven serial device driver suitable for eCos
applications for all on-chip serial devices. The serial driver
consists of an eCos package:
CYGPKG_IO_SERIAL_CORTEXM_LM3S which provides
configuration for the
package. Using the HAL diagnostic I/O support, any of these
devices can be used by the ROM monitor for
communication with GDB. If a device is needed by the application,
either directly or via the serial driver, then it cannot also be
used for GDB communication using the HAL I/O support. An
alternative serial port should be used instead.
The HAL defines CDL interfaces,
CYGINT_HAL_LM3S_UART4 for each of the possible
UARTs. At present no LM3S device has more that 3 UARTs, so these
interfaces contain support for future expansion. The platform HAL
CDL should contain an
implements directive for each such UART that
is available for use on the board. This will enable use of the
UART for diagnostic use.
The LM3S UARTs provide only TX and RX data lines, although the PL011 macrocell is theoretically capable of RTS/CTS flow control.
The LM3S HAL relies on the architectural HAL to provide support
for the interrupts directly routed to the NVIC. The
cyg/hal/var_intr.h header defines
the vector mapping for these.
The variant HAL provides support for packaging the configuration of a GPIO line into a single 32-bit descriptor that can then be used with macros to configure the pin and set and read its value.
The variant HAL provides support for packaging the clock control parameters of a device into a single 32-bit descriptor that can then be used with macros to enable and disable the device's clock.
The variant HAL provides a driver for the I²C bus device. There
is a configuration
defines the clock speed at which the bus operates. The platform
HAL must define the set of devices attached to the bus.
The SSI device is based on the ARM PL022 SSP primecell and SPI
support is provided via the
CYGPKG_DEVS_SPI_ARM_PL022 driver. The
platform HAL must define the bus instances and devices attached
The LM3S HAL contains support for gprof-base
profiling using a sampling timer. The default timer used is Timer
0. The timer used is selected by a set
src/lm3s_misc.c which can be changed to
refer to a different timer if required. This timer is only
CYGPKG_PROFILE_GPROF is enabled,
otherwise it remains available for application use.
The platform HAL must provide the input clock frequency
CYGARC_HAL_CORTEXM_LM3S_INPUT_CLOCK) in its
CDL file. This is then combined with the following options defined
in this package to define the default system clocks:
This defines the source of
the main system clock. It can take one of six values:
INTselects the internal ocillator,
INTby4selects the internal ocillator divided by 4,
MAINselects the main ocillator,
PLLselects the PLL,
30Kselects the 30KHz internal clock,
32Kselects the 32KHz internal clock. It defaults to
- This defines the divider applied to the 400MHz PLL output to generate the system clock. This can take values between 1 and 16. The default value is 4, giving a 50MHz system clock.
- This defines the prescaler divider for the Pulse Width Modulator. It may take any power of 2 value between 1 and 64. The default is 1.
The actual values of the system clock, in Hz, is stored in the
hal_lm3s_sysclk. The clock
supplied to the SysTick timer, SYSCLK/4, is also assigned to
hal_cortexm_systick_clock. These variables are
used, rather than configuration options, in anticipation of future
support for power management by varying the system clock rate.
|2023-01-12||eCosPro Non-Commercial Public License|