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The boot code in the BCM7241 instructs it to continue the boot process by reading additional code from the onboard NAND flash, which can be updated in the field, either from a SDHC/SDXC flash card or a USB mass-storage device. Part of the NAND flash is also used to hold non-volatile parameters. The contents of the boot flash are copied into the SDRAM. The CPU then jumps to the boot code.
SDRAM
The HD222 and HD1022 contain a single bank of DDR SDRAM, consisting of two 16x256MB chips (1GB total). When the CPU boots, it will copy the code from the NAND flash device into the SDRAM and then execute the code from the SDRAM. The SDRAM runs at a clock rate of 933MHz, with a data rate of 1866MT/s.
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The audio output is fed through an amplifier and sent directly to the audio output jack. It can drive a 32Ω load with a 2V RMS signal.
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There are four on-board LEDs that indicate the following:
LED | Indication | |
Green power (Pwr) | Displays when the board is powered up and not in reset mode. | |
Green file-system activity (Bsy) | Flashes any time there is file-system activity (on any storage device) | |
Yellow update (Upd) | Flashes when the board is being upgraded. | |
Red status (Err) | Flashes a certain number of times to indicate which error is occurring. The flash codes are described below. | |
2 | Unspecified error | |
3 | Network recovery script is preparing to run on a device configured for network recovery. | |
4 | No upgrade file found. | |
5 | Failed to load kernel module. | |
6 | Board is not capable of running the current firmware version. | |
7 | A piece of on-board hardware is not working correctly. | |
8 | Problem related to the storage device (either the USB drive or SD card) | |
9 | Problem related to the registry/NAND | |
10 | The autorun script encountered a load/run error. | |
11 | WiFi-related error (mainly, WiFi not found on USB) | |
12 | Unable to find a bootable image. | |
On-Board Switch
The on-board switch is connected to the GPIO12, which is pulled low when the service (SVC) button is pressed. Conversely, a pull-up on the button normally sets the GPIO12 to be pulled high.
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The USB 2.0 high-speed host controller is implemented internally on the BCM7241 SOC. The board utilizes over-current protected switches that can be used to turn the power to USB devices on or off (or to detect over-current situations).