Atmel DataFlash memory devices require a slightly different command sequence to load data for booting. The boot kernel of some Blackfin processors (ADSP-BF531/BF532/BF533/BF538/BF539) has a special built-in mode to accommodate these needs. If the SPI master mode is selected, the boot kernel performs a device detection sequence by issuing a 0x03 command followed by a zero address to the SPI bus. The SPI then counts cycles until data other than 0xFF (due to the pull-up on MISO) is returned. If no data is returned after three address bytes are issued, the boot kernel assumes that an Atmel DataFlash device might be out there and activates the required reading mode.
The above method works fine with the AT45DBxxxB parts from Atmel. However, with Atmel’s later AT45DBxxxD family of parts, the behavior changes slightly. The AT45DBxxxD DataFlash devices respond to the 0x03 command. However, they do not meet standard SPI addressing modes because of the DataFlash’s default page size of 264, 528, or 1056 bytes (depending on the device density). As a result, the boot kernel will properly read the first page of the memory and fail in reading all other pages.
All newer AT45DBxxxD DataFlash devices support the "power-of-2" (Binary) addressing mode. In this mode, the page size is limited to standard sizes (256, 512, ... bytes). The part responds to 0x03 (and also to 0x0B) commands and, therefore, behaves like a standard 3-byte addressable SPI memory.
DataFlash devices in power-of-2 mode can boot all existing Blackfin processors.
A One-Time-Programmable Bit has to be programmed by a special command to place an off-the-shelf DataFlash device into this power-of-2 (binary) page mode. Recent DataFlash devices no longer require a subsequent power cycle in order for the power-of-2 mode to be activated once the bit has been programmed. Please consult the respective device datasheets for further details. Additionally, Atmel is offers factory-configured power-of-2 page size devices with trailing 'SL954 or SL955' part number signatures where the OTP bit is factory-programmed.
An applications article http://www.atmel.com is available for reference on ordering factory-configured power-of-2 page size devices.
More recent Blackfin boot kernels (those embedded on ADSP-BF51x, ADSP-BF50x, ADSP-BF592, ADSP-BF52x and ADSP-BF54x processors) no longer have special support for DataFlash memories. Instead, it is assumed that all customers are using the 'D' Family of devices and have the option to let the part operate in power-of-2 mode.
DataFlash is a registered Trademark of Atmel Corporation.