This implements the principle of "least surprise", in that users won't
normally expect to start overwriting an existing file on these devices.
Real hardware didn't behave that way. A new (empty) file can always
be created with the -N switch on the ATTACH.
If the nested indirect/execute limit (INDMAX, XCTMAX) is set to 0, the simulator will loop indefinitely in an indirect address or execute loop, testing for interrupts before each memory reference. Thus, on an infinite loop, the simulator will never complete the instruction, but the instruction is interruptible. So for example, under TOPS-10:
.r ddt
1/ 0 jrstf @1
1$g
^C
^C
.
The JRSTF will never finish, but it can be interrupted by any device, and double ^C will return control to the command line.
If INDMAX or XCTMAX is non-zero, the previous behavior of limiting loops to a specific depth is retained. However, the default value is now 0.
This closes issue #218.
Conflicts:
doc/pdp10_doc.doc
