Eight Bit Devices - Sun Microsystems SPARCstation 2 Service Manual

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Eight Bit Devices

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The eight-bit devices connected to the I/O data bus consist of the following:
•
Boot PROM
The boot PROM (see Figures 1-3 and 1-4) is connected to the I/O data bus.
The boot PROM is 256Kx8 in size and contains the boot code, diagnostics,
and the Forth Toolkit, signified by the ok prompt. The Forth Toolkit does
not look like other Sun Monitor programs and does not behave like the
older Sun PROMs.
The boot PROM does the following:
a. Runs startup diagnostic tests.
b. Initializes the host machine.
c. Reads non-volatile RAM (NVRAM) and executes the boot sequence.
Usually, this consists of booting SunOS. In some cases, however, the
SunDiagnostic Executive or standalone programs can also be run. For
more information on the boot sequence, see "How It Fits Together" in
Chapter 2.
d. Supplies program code for the abbreviated system monitor, signified by
the > prompt and the Forth Toolkit. If the boot attempt fails, the boot
PROM tries to start the abbreviated system monitor.
e. Supplies program code for the on-board diagnostics accessible through
the Forth Toolkit. For more information on the on-board diagnostics, see
"Boot PROM Diagnostics" in Chapter 2.
•
Non-volatile RAM (NVRAM) and Time-of-Day Clock
The NVRAM chip (see Figures 1-3 and 1-4) contains the time-of-day clock
and the non-volatile RAM. The NVRAM chip is connected to the I/O data
bus.
The NVRAM chip contains its own battery. There is no limit on the number
of times the NVRAM chip can be written to.
The non-volatile RAM stores the default system configuration parameters.
The default parameters are listed in Appendix D. This defines how the
system will be set up at the lowest level. You can modify these parameters
SPARCstation 2 Field Service Manual—February 1991