Nonvolatile Ram; Nvram Access - DEC Digital Alpha VME 4/224 User Manual

9.9 Nonvolatile RAM

Digital Alpha VME 4 offers just under 32 KB of battery backed-up on-board
SRAM. The RAM is provided by the DS1386 chip and is held nonvolatile by the
built-in lithium battery source.
The memory is read/write accessible in Nbus space. In effect, the DS1386
chip (TOY clock, watchdog timer, and NVRAM) contains 32 KB read/write
byte elements. The lowest 14 of these bytes have special register functions for
operation of the TOY clock and watchdog timer. The remaining bytes, 32 KB-14,
are usable as general-purpose bytewide read/write RAM.
This RAM is organized as contiguous bytes starting at TOY_BASE_ADDR+0x0E
through TOY_BASE_ADDR+7FFF, as shown in Figure 9–20.
Figure 9–20 NVRAM Access
TOY_BASE_ADDR + 000E :
TOY_BASE_ADDR + 000F :
TOY_BASE_ADDR + 7FFF :
As for the TOY clock operation, module switch 1 allows the VMEbus 5VSTDBY to
be connected to the DS1386 giving RAM backup that is independent of both the
normal 5 V supply and the internal lithium battery.
The firmware uses NVRAM for module parameters and settings, and error and
failure information.
The lowest 16 KB of the battery backed-up RAM is reserved for firmware usage.
Thus, user and O/S code should not access NVRAM below the address of TOY_
BASE_ADDR+0x4000.
9–36 Nbus
07 06 05 04 03 02 01
Read/Write
Read/Write
.
.
.
Read/Write
00
ML013302