In order to support unique TFTP boot directories for each Raspberry Pi the bootloader prefixes the filenames with a device specific directory. If neither start4.elf nor start.elf are found in the prefixed directory then the prefix is cleared.On earlier models the serial number is used as the prefix, however, on Raspberry Pi 4 the MAC address is no longer generated from the serial number making it difficult to automatically create tftpboot directories on the server by inspecting DHCPDISCOVER packets. To support this the TFTP_PREFIX may be customized to either be the MAC address, a fixed value or the serial number (default).
In earlier releases the client GUID (Option97) was just the serial number repeated 4 times. By default, the new GUID format isthe concatenation of the fourcc for RPi4 (0x34695052 - little endian), the board revision (e.g. 0x00c03111) (4-bytes), the least significant 4 bytes of the mac address and the 4-byte serial number.This is intended to be unique but also provide structured information to the DHCP server, allowing Raspberry Pi 4 computers to be identified without relying upon the Ethernet MAC OUID.
This option may be set to 0 to block self-update without requiring the EEPROM configuration to be updated. This is sometimes useful when updating multiple Raspberry Pis via network boot because this option can be controlled per Raspberry Pi (e.g. via a serial number filter in config.txt).
From this point the bootcode.bin code continues to load the system. The first file it will try to access is [serial_number]/start.elf. If this does not result in an error then any other files to be read will be pre-pended with the serial_number. This is useful because it enables you to create separate directories with separate start.elf / kernels for your Raspberry Pis.To get the serial number for the device you can either try this boot mode and see what file is accessed using tcpdump / wireshark, or you can run a standard Raspberry Pi OS SD card and cat /proc/cpuinfo.
The above uses the mailbox property interface GET_BOARD_SERIAL with a request size of 8 bytes and response size of 8 bytes (sending two integers for the request 0, 0). The response to this will be two integers (0x00000020 and 0x80000000) followed by the tag code, the request length, the response length (with the 31st bit set to indicate that it is a response) then the 64-bit serial number (where the MS 32 bits are always 0).
The LoSSI standard allows issuing of commands to peripherals (LCD) and to transfer data to and from them. LoSSI commands and parameters are 8 bits long, but an extra bit is used to indicate whether the byte is a command or parameter/data. This extra bit is set high for a data and low for a command. The resulting 9-bit value is serialized to the output. LoSSI is commonly used with MIPI DBI type C compatible LCD controllers.
- The product serial number or production date code as specified on the product. The model number, the serial number or production date code (if available) can be found in the battery compartment or on the back or bottom of the product.
MacRumors previously reported about Apple's plan to switch to randomized serial numbers for future products starting in early 2021, and this transition has now started with the new purple iPhone 12 model in multiple countries.
With assistance from Aaron Zollo, host of the YouTube channel ZolloTech, we can confirm that the purple iPhone 12 released last month has a new 10-character serial number format, compared to the usual 12 characters for most other Apple products. Apple previously said its randomized serial numbers would initially be 10 characters long, so the purple iPhone 12 appears to be the first Apple product with a randomized serial number.
The change likely extends to the purple iPhone 12 mini, but we've yet to confirm this. On the contrary, the randomized serial number format does not appear to apply to the AirTag at this time, with multiple MacRumors editors and others we've spoken to still seeing 12-character serial numbers for the item tracking accessory.
In a memo obtained by MacRumors in March, Apple said products already shipping at that time would continue to use the company's previous serial number format, which has for years allowed customers and service providers to determine the date and location that a product was manufactured. The first three characters represent the manufacturing location, the following two characters indicate the year and week of manufacture, and the last four characters reveal a device's model, color, and storage capacity.
The new serial number format will consist of a randomized alphanumeric string of 8-14 characters (10 characters initially) that will no longer include manufacturing or configuration details, according to Apple's memo. Apple advised authorized resellers to prepare for the transition to the new format ahead of its "Spring Loaded" event last month. 2b1af7f3a8