Eurotech Appliances PXA255 Memory, SDRAM interface, FLASH memory/silicon disk

VIPER Technical Manual	Detailed hardware description

Memory

The VIPER has four types of memory fitted:

•1MB of bootloader FLASH containing Redboot to boot embedded Linux or VxWorks, or Eboot to boot Windows CE.

•A resident FLASH disk containing the OS and application images.

•SDRAM for system memory.

VL • 256KB Static RAM (SRAM).

A 1MB Bottom Boot FLASH EPROM device, arranged as 512Kbit x 16, is used as the bootloader FLASH. It holds Redboot (for embedded Linux or VxWorks) or Eboot (for Windows CE), together with configuration information. When the microprocessor comes out of reset it boots the relevant bootloader from here, which in turn boots up the OS from the FLASH memory/silicon disk. Whenever the Bootloader FLASH memory is accessed the FLASH access LED illuminates.

FLASH memory/silicon disk

The VIPER supports 16MB or 32MB of Intel StrataFLASH memory for the OS and application images. The FLASH memory is arranged as 64Mbit x 16-bits (16MB device) or as 128Mbit x 16-bits (32MB device) respectively.

The FLASH memory array is divided into equally sized symmetrical blocks that are

64-Kword in size. A 128Mbit device contains 128 blocks, and 256Mbit device contains 256 blocks. Flash cells within a block are organized by rows and columns. A block contains 512 rows by 128 words. The words on a row are divided into 16 eight-word groups.

The PXA255 GPIO14 pin is connected to the FLASH memory status output. This pin can be used to generate an interrupt to indicate the completion of a CFI command.

Whenever the FLASH memory is accessed the FLASH access LED illuminates.

SDRAM interface

There are two memory configurations supported by the VIPER: 16MB or 64MB of SDRAM located in Bank 0. The SDRAM is configured as 4MB x 32-bits (16MB) or 16MB x 32-bits (64MB), by 2 devices with 4 internal banks of 1MB or 4MB x 16-bits.

These are surface mount devices soldered to the board and cannot be upgraded. RedBoot (embedded Linux and VxWorks) automatically detects the amount of memory fitted to the board, and configures the SDRAM controller accordingly. For Windows CE applications the SDRAM memory will always be 64MB.

The SDRAM controller supports running the memory at frequencies between 50MHz and 99.5MHz (default). This can be configured to achieve the optimum balance between power consumption and performance.