Implementation
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The 167Bug firmware requires 2KB of NVRAM for storage of board
configuration, communication, and booting parameters. This storage area
begins at $FFFC 16F8 and ends at $FFFC 1EF7.
167Bug requires a minimum of 64KB of contiguous read/write memory to
operate. The ENV command controls where this block of memory is
located. Regardless of where the onboard RAM is located, the first 64KB
is used for 167Bug stack and static variable space and the rest is reserved
as user space. Whenever the MVME167P is reset, the target Program
Counter (PC) is initialized to the address corresponding to the beginning
of the user space, and the target stack pointers are initialized to addresses
within the user space, with the target Interrupt Stack Pointer (ISP) set to
the top of the user space.
Implementation
167Bug is written largely in the C programming language, providing
benefits of portability and maintainability. Where necessary, assembly
language has been used in the form of separately compiled program
modules containing only assembler code. No mixed-language modules are
used.
Physically, 167Bug is stored in two 27D4002 44-pin EPROMs installed in
sockets XU1 and XU2. The executable code is checksummed at every
power-on or reset firmware entry, and the result (which includes a
precalculated checksum contained in the memory devices) is tested for an
expected zero. Modifying the contents of the memory devices is
discouraged, unless you take precautions to re-checksum.
Using the Debugger
167Bug is command-driven; it performs its various operations in response
to commands that you enter at the keyboard. When the
167-Bug
prompt
appears on the screen, the firmware is ready to accept debugger
commands. When the
167-Diag
prompt appears on the screen, the
firmware is ready to accept diagnostics commands. To switch from one
mode to the other, enter SD.
Содержание MVME167P
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