Overview

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.

Startup

The platform HAL package supports four separate startup types:

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.

PWM Driver

PWM is supported by the CYGPKG_DEVS_PWM_BCM driver. The PWM device supports two channels connected to four pins available on the GPIO header. Channel 0 is connected to GPIO12 and GPIO18, pins 12 and 32 on the GPIO header. Channel 1 is connected to GPIO13 and GPIO19, pins 33 and 35 on the GPIO header. Note that some of these may clash with other uses of the same pins, particularly GPIO19 which is also SPI MISO.

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 mass storage devices, serial devices including 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.

The option CYGPKG_DEVS_ETH_LAN951X_SHORT_CIRCUIT controls whether the Ethernet driver uses the Raspberry Pi board type to decide whether the board contains an Ethernet device. If it does not, then initialization of the driver and the entire network stack is prevented, saving startup time. This option can be misled if, for example, a Compute Module is plugged in to a carrier board that has a LAN951X/LAN7515 installed. So by default the option is only enabled for RedBoot builds, and not for eCos builds, where the user is expected to know what they are doing. If the default is not as reqired, it can be changed in the ConfigTool.

WiFi Driver

Support for the wireless network is provided by the CYGPKG_NET_WIFI_BROADCOM_WWD driver. The majority of the wireless configuration is fixed based on the RPi platform configured with no user configuration required. It is enabled by default when the appropriate packages are included in the configuration.

The WiFi chipsets used in the Raspberry Pi platforms require 3rd-party binary firmware images for correct operation. See the WICED specific Chipset Firmware section for details covering the RPi specific images.

The option CYGPKG_HAL_ARM_CORTEXA_PI_WICED_DCT controls whether the WICED Device Configuration Tables (DCT) support is enabled. The enabled functionality can be used by the WICED SDK, and the application world, to hold persistent WiFi configurations.

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.

Frequency Control

eCos does not contain any support for dynamic frequency management in the same way that Linux does. The CPUs run at a single frequency throughout. Normally this is the maximum frequency permitted without overclocking. A different frequency may be selected in the configuration, or it may be set at runtime by calling hal_bcm283x_set_freqencies(). See the BCM283X HAL for details.

The option CYGHWR_HAL_ARM_CORTEXA_BCM283X_ARM_FREQ defines the frequency in MHz at which the ARM CPU will run. For RAM startup types, the default value of zero will cause the application to continue using the frequency set up by RedBoot. For other startup types, a value of zero will cause the HAL to select a default frequency based on the board type. A non zero value will force the CPU frequency to the given value.

The option CYGHWR_HAL_ARM_CORTEXA_BCM283X_CORE_FREQ defines the frequency in MHz at which the GPU will run. For RAM startup types, the default value of zero will cause the application to continue using the frequency set up by RedBoot. For other startup types, a value of zero will cause the HAL to select a default frequency based on the board type. A non zero value will force the CPU frequency to the given value.

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: