Configuration — Platform-specific Configuration Options


The Raspberry Pi platform HAL package is loaded automatically when eCos is configured for any RPi 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.


The platform HAL package supports four separate startup types:

This startup type is normally used during application development when using the RedBoot ROM monitor. arm-eabi-gdb is used to load the RAM startup application into memory and debug it. It is assumed that the hardware has already been initialized by RedBoot. By default the application will use the eCos virtual vectors mechanism to obtain services from RedBoot, including diagnostic output.
This startup type can be used for finished applications which will be booted direct from the SD card. The application will be self-contained with no dependencies on services provided by other software. eCos startup code will perform all necessary hardware initialization. This startup type can also be used for applications loaded via JTAG for testing prior to committing to an SD card.
This startup type can be used for finished applications that are to be loaded by a JTAG debugger. The application will be self-contained with no dependencies on services provided by other software. eCos startup code will perform all necessary hardware initialization. This startup type can also be used for applications loaded via JTAG.
This startup type can be used for finished applications that can be loaded into RAM via RedBoot or via a JTAG debugger. The load address is set to the same as for RAM applications, however, the application will be self-contained with no dependencies on services provided by other software. eCos startup code will perform all necessary hardware initialization. Once started, this application takes full control of the system and RedBoot will not be called again. This means that debugging via RedBoot will not be possible, only JTAG-based hardware debugging is supported. The intent of this startup type is to allow SMP test programs to be run from RedBoot, most SMP applications should use the ROM startup type.

The main difference between ROM, JTAG and SMP startup types is the address at which they are loaded. ROM applications load at 0x00008000, which is the default address used by the GPU boot loader. JTAG applications load at 0x00100000, leaving the lower 1MiB free for a ROM RedBoot. This is necessary because in multi-core systems, the secondary cores will be looping in code in the RedBoot executable, and we don't want to overwrite that, since it may cause these cores to run wild. SMP applications load at 0x00200000, leaving the lower 2MiB free. This allows either a ROM or JTAG RedBoot to be used to load it without affecting the secondary cores. For the same reasons, RAM applications also load at the 0x00200000 boundary.

RedBoot 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 RedBoot.

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.

UART Serial Driver

The auxiliary mini UART is 16550 compatible and is supported by the CYGPKG_IO_SERIAL_GENERIC_16X5X generic driver package which is modified by the CYGPKG_IO_SERIAL_ARM_BCM283X driver package for the Raspberry Pi family. By default the UART used only the TXD0 and RXD0 pins connected to GPIO14 and GPIO15 on the GPIO header. While RTS and CTS could be made available on GPIO16 and GPIO17, this is not currently supported since these pins are better left for other purposes. The mini UART is also lacking some 16550 functionality, it is only capable of 7 or 8 bit characters, and only supports one stop bit and no parity; attempts to select other settings will be accepted, but will have no effect. Since the TXD0 and RXD0 pins are not at RS232 levels it is necessary to either connect an RS232 transceiver to them or, more usually, an FTDI USB serial convertor module.

SPI Driver

SPI0 is supported by the CYGPKG_DEVS_SPI_ARM_BCM283X. The auxiliary SPI1 and SPI2 devices are not currently supported. By default the MISO, MOSI and SCLK signals are connected to GPIO9, GPIO10 and GPIO11 respectively. The chip select signals are connected to GPIO7 and GPIO8. These pins are managed in GPIO mode, so it is possible to add extra SPI devices by assigning additional GPIO pins to act as chip select lines.

I²C Driver

I2C1 is supported by the CYGPKG_DEVS_I2C_BSC driver. The SDA1 and SCL1 signals are connected to GPIO2 and GPIO3 pins. I2C0 is used by the GPU to operate the ID_SD and ID_SC pins as well as the GPIO extender in the Compute Modules; I2C2 is dedicated to the HDMI interface; so neither of these is available for use.

USB Support

USB is supported by the CYGPKG_IO_USB package USB protocol stack together with the CYGPKG_DEVS_USB_DWC host controller driver. The stack will recognize and support the USB hub component of the LAN951X/LAN7515 when it is available on the board, together with any hubs that might be plugged in to that. The stack currently only supports CONTROL and BULK transfer types, INTERRUPT and ISOCHRONOUS transfers are not supported. The host controller driver currently supports High, Fast and Low speed devices. USB support is currently oriented towards supporting USB memory drives, CDC/ACM and FTDI serial adaptors and the LAN951X/LAN7515 Ethernet component.

Ethernet Driver

Support for the LAN951X/LAN7515 Ethernet component is provided by the CYGPKG_DEVS_ETH_LAN951X driver. This driver is dependent on the USB stack and can only be configured if the USB stack is also present. This driver is also not active until the generic Ethernet support package, CYGPKG_IO_ETH_DRIVERS, is included in the configuration.

MMC/SD Driver

Support for the SD/MMC socket is provided by the CYGPKG_DEVS_MMCSD_SDHOST driver. This uses the Broadcom SDHOST controller; the Arasan SDHCI controller is not currently supported, although in future it will be used for the CYW43438 WiFi device on the Pi3 and CM3. On the compute modules, this same driver provides access to the eMMC device.

The MMC/SD bus driver layer (CYGPKG_DEVS_DISK_MMC) is automatically included as part of the hardware-specific configuration for these targets. All that is required to enable MMC/SD support is to include the generic disk I/O infrastructure package (CYGPKG_IO_DISK), along with the intended filesystem, typically, the FAT filesystem (CYGPKG_FS_FAT) and any of its package dependencies (including CYGPKG_LIBC_STRING and CYGPKG_LINUX_COMPAT for FAT).

While earlier variants of the Raspberry Pi had a card detect signal from the SD card socket attached to a GPIO line, this has been dropped in later variants. It also makes no sense for the permanently connected eMMC devices on the compute modules. Therefore, card detection is not currently supported on any RPi boards, so the disk IO layer's removable media support cannot detect card insertion or removal, and the FILEIO layer's automounter cannot currently be used.

GPIO Support

GPIO support is provided by the BCM283X variant HAL , and is documented there. The GPIO API is built around descriptors that encode a GPIO pin number together with its function (IN, OUT or device function) and mode into a single 32 bit value. The mode includes edge and level interrupt recognition and pull up and down settings. The eCosPro subsystem also decoded all GPIO interrupts into separate vectors.

Compiler Flags

The platform 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. The following flags are specific to this port:

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. For the BCM2835 variants that contain a single ARM11 CPU, (Pi0, Pi1, CM1), this option should be selected.
For the BCM2836, containing 4 Cortex-A7 CPUs and the BCM2837, containing four Cortex-A53 CPUs, this option should be selected. While the Cortex-A53 is strictly a ARM64 CPU, we can only use it in ARM32 mode, where it supports the same instruction set as the Cortex-A7. So, for simplicity we use the same option for both.
The arm-eabi-gcc compiler will compile C and C++ files into the Thumb2 instruction set when this option is used. The best way to build eCos in Thumb mode is to enable the configuration option CYGHWR_THUMB.