The current implementation of "run_cmd" in scp.c calls "fprint_stopped_gen" (via "fprint_stopped") to print the message associated with the "sim_instr" return status. Messages associated with VM stops must be provided to the SCP via the "sim_stop_messages" array.
"fprint_stopped_gen" prints the status message in a rigid format: the message string, a comma, the program counter register name, a colon, the current PC value, and the instruction at that address in symbolic format.
For example:
HALT instruction, P: 24713 (LDA 1)
Only the message string is under the control of the VM. If additional information is needed, it can only be added before the first comma.
The HP2100 simulator does this for halt instructions, which contain device select code and flag hold/clear bit fields that, in practice, are used to communicate to the operator the significance of the particular halt encountered, rather than to affect the device interface:
HALT instruction 102077, P: 24713 (LDA 1)
To implement this, the simulator must define the message as a variable and then copy the formatted octal value into the buffer at the appropriate location before returning from "sim_instr".
However, if the VM wants to display a different register value, e.g.:
Self test #13 complete, STAT: 000020
...this cannot be done without also displaying the program counter, which may be irrelevant for the given stop condition.
001. PROBLEM: Cannot show radix, etc. for a device that has no modifiers.
OBSERVATION: The default data radix for a device may be set with the SET
<dev> OCT|DEC|HEX command. However, if the device does not have a modifier
table, SHOW <dev> RADIX is rejected with "No settable parameters".
The same problem occurs for SHOW <dev> DEBUG and SHOW <dev> NAMES. For a
device that provides debug printouts, SHOW <dev> MOD will list "DEBUG,
NODEBUG" among the modifiers, and the SHOW <dev> DEBUG command will display
the current debug status. However, if the device does not contain a
modifier table, SHOW <dev> MOD and SHOW <dev> DEBUG will report "No
settable parameters", even though SET <dev> DEBUG is accepted and works as
expected. For such a device, SHOW MOD will show "DEBUG, NODEBUG" as
acceptable modifiers.
002. PROBLEM: SET and SHOW responses for invalid entry are inconsistent.
OBSERVATION: Entering SET <dev> <mod> where <mod> is not defined in the
device's modifier table displays "Non-existent parameter." Entering SHOW
with the same parameters displays "Invalid argument."
Similarly, entering SET <dev> DEBUG for a device that does not have
debugging capability displays "Command not allowed." Entering SHOW with
the same parameters displays nothing.
In both cases, the messages displayed should be the same for the same
error.
OBSERVATION: For a simulator stop, sim_vm_fprint_addr (if defined) is
called to print the value of the program counter, regardless of whether or
not the register was defined with REG_VMAD. However, displaying the PC
value with "examine" calls sim_vm_fprint_addr only if the REG_VMAD flag is
present. The displayed value of the PC should be the same in both cases.
Make sure to properly support multiple receive buffers by correctly setting the data length read and the appropriate buffer descriptor status bits for each buffer descriptor that is used to hold a packet.
- removed cycle counting in CPU, the sim_interval issue
- fixed the Console multiplexer logic; it now works with SET REMOTE TELNET= and SET CONSOLE TELNET=
- commented testhdt.sim
- changed run.cmd to try to execute either VStudio or mingw executable, in this order.
- changed printf messages to use sim_printf
Possible issues remaining:
- timer device polling, not yet debugged, the rate of 1.25MHz is likely still incorrect, so UCSD wall clock is surely wrong
- few instructions still to be trapped by opcode.debug - I haven't seen them in life code yet
- HD device still not yet finished; I'll pick this up again soon
