Vax 613 0S Manuel d'instructions Page 186

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Pressing the HALT button causes entry into the system ROM code by means of a
PAL halt, which further determines whether a HALT or a Reboot is required.
Note
HALT can be masked out. Refer to the DECchip 21064-AA Microprocessor
Hardware Reference Manual under HIER.
Chapter 13 discusses DEC 3000 firmware ROMs in detail.
11.1.1 Power-On Reset Sequence
Upon assertion of RESET, the ASICs and PALs force their registers into a known
state. RESET also initializes a number of IPRs in the CPU and induces the CPU
to read the contents of a SROM into its Icache. The CPU then executes this code
in the PALcode environment.
11.1.2 SROM Sequence
The SROM code performs the following:
1. Initializes and enables the CPU caches and the external Bcache. However, if
an error is discovered during Bcache set up, SROM code disables the Bcache
and continues with non-cacheable memory references.
2. Determines the amount of memory contained in the system and configures
the memory. (See Section 3.2.3 and Section 4.1.)
3. Check memory until it locates a good contiguous 2 MB portion (8 KB aligned)
to accommodate the system-ROM (SYSROM) code.
4. Test the path to the SYSROM:
In 300/400/600/700 models, it is connected to the IOCTL ASIC.
In 500/800/900 models, half is connected to the SFB ASIC and half to the
IOCTL ASIC.
5. Copy the system ROM (SYSROM) into memory.
6. Transfer control to the SYSROM code.
11.1.3 SYSROM Sequence
The SYSROM code performs the following:
1. Completes initialization not performed by the SROM (for example, CXTurbo
and SCSI).
2. Performs power-on self test—sequential self-test (pin level) of stuck-at faults.
3. Performs console program initialization—set up console I/O
4. Executes console routines:
a. Handle input and output to console device; parse commands and call
appropriate routines
b. Interface with the operating system and Diagnostic firmware
c. Automatically invoke MIPS interpreter for TURBOchannel options.
5. Starts primitive boot drivers—SCSI controller and LANCE Ethernet
controller
11–2 CPU Power Up and Initialization
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