RAM 6.0 BUX II Series Betriebsanweisung PDF herunterladen (Seite 12)

VxWorks

Hardware Considerations Guide, 6.0

RAM

VxWorks CISC processors require 1 MB of RAM for a development system that

includes the standard VxWorks features, such as the shell, network, file system,

loader, and others. RISC processors typically require more RAM space: 2 MB of

RAM is the minimum; 4 MB is encouraged. For a scaled-down production system,

the amount of RAM required depends on the application size and the options

selected.

ROM

VxWorks CISC processors require a minimum of 128 KB of ROM, which is just

sufficient for stripped-down VxWorks compressed boot ROMs on most CISC

architectures. For most CISC-based systems, 512 KB of ROM is preferred. RISC

processors typically require greater ROM space; 512 KB of ROM is considered a

minimum, because compressed boot images are typically greater than 256 KB in

size. Many full-features vxWorks images can be larger than 1 MB therefore, 2 MB

of ROM is preferred. If you are using TrueFFS, and the same flash bank will contain

both a VxWorks image and a file system, more flash is required.

Applications running from ROM are usually slow because of 16-bit or (more

commonly) 8-bit data width, slow access times, and so on. VxWorks avoids this

problem by typically copying the contents of the boot ROMs into RAM. However,

ROM-resident VxWorks images are supported on most BSPs. For information on

which image types are supported, refer to the BSP.

Non-Volatile RAM

VxWorks can use 255 or 512 bytes of non-volatile RAM (NVRAM) for storing the

boot line information. Without NVRAM, the correct boot line must either be

burned into the boot ROMs or typed in after every reset/power-up during

development.

NVRAM can be implemented with battery-backed static RAM, EEPROM, or other

technology. A number of boards use the Mostek MK48T02 or Dallas

Semiconductor 1643, both of which contain a time-of-day clock in addition to

battery-backed static RAM. In this case, the time-of-day clock is not used by

VxWorks.

Refer to the man page for the appropriate memory driver for more information on

configuring a specific driver. Almost all drivers use the configuration macros

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RAM 6.0 BUX II Series Betriebsanweisung Seite 12