4Kx42 Theory of Operation
This page describes how specific components operate on BrightSign 4K players.
Power Supply
There are several voltage levels present in BrightSign 4K players.
Reset
BrightSign 4K players have a Low Voltage Reset circuit. This circuit will hold the RESET_L signal low until a valid 3.3V power source is present.
BCM7444 / 7252 CPU
The 4K242 and 4K1042 utilize a BCM7252 CPU, while the 4K1142 utilizes a BCM7444 CPU. The CPU is reset by the RESET_L signal from the low voltage reset circuit going into the RESET_IN pin on the CPU. When the RESET_IN pin goes from low to high, the CPU will boot from the NAND flash.
Built-in Flash
The boot code in the BCM7252/BCM7444 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 4K1142 contains six banks of DDR SDRAM (two 4GB banks and four 2GB banks), while the 4K242 and 4K1042 each contain four banks of DDR SDRAM (two 2GB banks and two 4GB banks). 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 1067MHz, with a data rate of 2133MT/s.
Serial Port
The 4K1042 and 4K1142 have a built-in UART that communicates with the RS-232 level shifter. The MAX232 uses a capacitive voltage switcher to create valid RS-232 voltage levels for the transmit pin.
Audio Outputs
BrightSign 4K players each have a single high quality audio DAC device, which takes in digital audio signals from the CPU in an I2S audio format. The AUD_LRCIN is the framing signal for the audio and runs at the frame rate of the audio source (usually either 44.1KHz or 48KHz). The AUD_BITCLK signal is typically 32 times higher than the AUD_LRCIN.
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.
On-Board LEDs
There are eight 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) |
Green MicroSD activity (µSD) | Displays when a MicroSD card is present. |
Green network activity (Svr) | Displays when the player is connected to the BrightSign Network. |
Green Ethernet activity (Eth) | Flashes when the player is connecting to the network. Displays when connected. |
Green WiFi activity | Flashes when the player is connecting to the wireless network. Displays when connected. |
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. |
| 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 |
| 13: The root file system has failed verification, which is used to detect whether the file system has been tampered with. You can recover a player that is showing this error code by performing a firmware update with secure boot. |
| 14: Boot loader failure |
Red/yellow combined | The Update (Upd) and Error (Err) LEDs may flash in unison to indicate that a player cannot connect to the BSN servers during the setup or recovery process. The red and yellow flash codes may also describe an error during the firmware update process as described below: |
| 2: Erase failed |
| 3: Write failed |
| 4: Verify failed |
| 5: Failed to find UBI partition |
| 6: Attempt to write unsigned CFE to unit with secure boot enabled |
| 7: Failed to find UBI partition |
| 8: Failed to create/attach UBI partition |
| 9: Unexpected error |
| 10: Upgrade script exited abnormally |
| 11: Upgrade took longer than expected |
| 12: Update completed but update file could not be deleted |
| 13: Firmware update file could not be read (from firmware v5.1.40) |
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.
Reset Switch / GPIO Button
The on-board switch is connected to the reset circuit. Pressing down the reset button will cause the GPIO07 to go low. Holding the reset button low for approximately 10 seconds will cause a hard reset. When the board goes into reset mode, the power LED will be dark until the reset button is released.
SDHC / SDXC and microSD Slots
The 4K series has one SDHC/SDXC and one internal microSD card slot, both capable of transferring a 25 Mbit/sec video stream, one 5.1 AC3 stream (pass-through), and three stereo PCM tracks simultaneously. There is no inherent limit on the storage capacity of SD cards used for 4K series players.
NAND Flash
BrightSign players have a built-in NAND flash. All the code for the player is stored on the NAND flash. It may also be possible to store some content on the NAND flash, which is connected directly to the CPU.
Ethernet
The 10/100/1000 Base-T Ethernet is implemented on 4K players by directly interfacing with the BCM7252/BCM7444. The player has on-board Ethernet magnetics and termination for the RJ-45 cable.
USB 2.0 / 3.0
The USB 2.0/3.0 high-speed host controller is implemented internally on the BCM7252/BCM7444 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.