273. ENHANCEMENT: Burst-fill only the first of two MPX receive buffers in FASTTIME mode.
OBSERVATION: When the 8-channel multiplexer is set for "optimized timing"
mode, buffered characters are transferred in blocks to and from the Telnet
connection. That is, the line service routine will send or receive
characters as long as they are available. This is more efficient than the
"realistic timing" mode, which sends or receives one character per service
invocation. Effectively, this means that up to 508 characters (two buffers
of 254 bytes each) may be sent or received between one CPU instruction or
DCPC cycle and the next. This works well for sending, but it can cause
buffer overflows when receiving.
Consider an application (such as Kermit) that receives large blocks of data
at high speed from a client. The multiplexer is designed to handle this
condition by interrupting the CPU when the first buffer is filled and
filling the second buffer while the CPU is unloading data from the first.
In realistic mode at 19,200 baud, the CPU has approximately 800
instructions or DCPC cycles available per character received. With a
second buffer of 254 bytes, the CPU has approximately 203,000 instructions
available to unload the first buffer after receiving the interrupt
notification. Once started, the DCPC transfer takes no more than 508
instruction times, so the CPU can easily keep up with data arriving at the
maximum baud rate.
In fast timing mode, however, the first buffer burst-fills in a single CPU
instruction time, and, if available from the Telnet connection, the second
buffer fills in the next instruction time. At that point, any additional
characters received will result in a buffer overflow condition. The
problem is that the CPU has no time between the first burst and the second
to empty the first buffer.
RESOLUTION: Modify "mpx_line_svc" (hp2100_mpx.c) to shift from burst
transfers to character-at-a-time transfers when a receive buffer is full
and awaiting unloading by the CPU. This allows the CPU and DCPC time to
read the buffer contents into memory before the second multiplexer buffer
is full. Once the completed buffer is freed, the service routine returns
to burst mode to fill the remainder of the other buffer, permitting the
efficiency of block transfers while avoiding buffer overruns with large
data transfers.
274. PROBLEM: A second connection to the BACI device leaves the client unresponsive.
OBSERVATION: The BACI device supports a single terminal client connection.
If a second connection is attempted, the client connects but is otherwise
unresponsive. It would be better if the client received the "All
connections busy" message that is reported by the terminal multiplexers
(MPX and MUX devices) when the number of connections is exceeded.
CAUSE: The "baci_poll_svc" is calling the "tmxr_poll_conn" routine only if
the port is not connected. The routine should be called unilaterally, so
that it will report an error and disconnect the client when all lines are
in use and another connection is attempted.
RESOLUTION: Modify "baci_poll_svc" (hp2100_baci.c) to call
"tmxr_poll_conn" unconditionally, so that a second concurrent connection
attempt will be rejected with "All connections busy".
275. PROBLEM: The exported program counter name (PC) clashes with other libraries.
OBSERVATION: In HP 21xx/1000 systems, the P register is the program
counter. In keeping with the naming of the other register variables (e.g.,
for A register, B register, etc.) in the simulator, the variable used
should be named "PR". However, for traditional reasons, the program
counter in SIMH is named "PC".
The main CPU module declares its hardware register variables as global, so
that they may be accessed by other CPU helper modules. Unfortunately, the
"curses" library also declares the symbol "PC" as global, leading to
conflicts when it is loaded by SCP. A workaround had been implemented that
renamed "PC" to "PC_Global" in the HP2100 simulator, but that meant that
the new name had to be used when debugging, which was awkward.
CAUSE: A poor choice of global symbol names from the "termcap" library,
which was inherited by the "curses" library.
RESOLUTION: Change the program counter variable name from "PC" to "PR"
(hp2100_cpu.c, hp2100_cpu1.c, hp2100_cpu2.c, hp2100_cpu3.c, hp2100_cpu4.c,
hp2100_cpu5.c, hp2100_cpu6.c, hp2100_cpu7.c, hp2100_dr.c, and hp2100_ipl.c)
to avoid a name clash and for register naming consistency.
265. PROBLEM: Compiling the HP simulator for 64-bit addressing produces many
conversion warnings.
OBSERVATION: Compiling the simulator and defining USE_INT64 and USE_ADDR64
with implicit conversion warnings enabled reveals a number of places where
assumptions were made that addresses would always be 32 bits. This is a
reasonable assumption, as there are no devices (CPU or peripherals) that
can handle gigabyte addressing. Still, many of these assumptions are not
necessary, and some future peripheral simulator may exceed this limit.
CAUSE: Future expansion to 64-bit addressing was not envisioned.
RESOLUTION: Modify source files to ensure that "t_addr" and "t_value"
types are used instead of "uint32" and "int32" types where addressing and
data values may be 64 bits. Also ensure that valid conversions to smaller
sizes use explicit casts.
266. PROBLEM: BOOT devices require a duplicate S-register declaration.
OBSERVATION: All of the peripheral devices that support the BOOT command
set the select code and other parameters into the S register during the
boot process. This direct register access requires an external declaration
that duplicates the one in the full CPU declarations file (hp2100_cpu.h).
A better method that avoids the duplicate declaration would be for the
"ibl_copy" routine to modify the S register on behalf of the caller.
CAUSE: Poor original implementation.
RESOLUTION: Modify "ibl_copy" (hp2100_cpu.c) to take two additional
parameters that clear and set bits, respectively, in the S register on
behalf of the caller. Modify the boot routines for the CPU, DA, DP, DQ,
DR, DS, IPL, MS, and PTR devices to use the new parameters instead of
modifying the S register directly.
The makefile now works for Linux and most Unix's. Howevr, for Solaris
and MacOS, you must first export the OSTYPE environment variable:
> export OSTYPE
> make
Otherwise, you will get build errors.
1. New Features
1.1 3.8-0
1.1.1 SCP and Libraries
- BREAK, NOBREAK, and SHOW BREAK with no argument will set, clear, and
show (respectively) a breakpoint at the current PC.
1.1.2 GRI
- Added support for the GRI-99 processor.
1.1.3 HP2100
- Added support for the BACI terminal interface.
- Added support for RTE OS/VMA/EMA, SIGNAL, VIS firmware extensions.
1.1.4 Nova
- Added support for 64KW memory (implemented in third-party CPU's).
1.1.5 PDP-11
- Added support for DC11, RC11, KE11A, KG11A.
- Added modem control support for DL11.
- Added ASCII character support for all 8b devices.
1.2 3.8-1
1.2.1 SCP and libraries
- Added capability to set line connection order for terminal multiplexers.
1.2.2 HP2100
- Added support for 12620A/12936A privileged interrupt fence.
- Added support for 12792C eight-channel asynchronous multiplexer.
2. Bugs Fixed
Please see the revision history on http://simh.trailing-edge.com or
in the source module sim_rev.h.
The makefile now works for Linux and most Unix's. Howevr, for Solaris
and MacOS, you must first export the OSTYPE environment variable:
> export OSTYPE
> make
Otherwise, you will get build errors.
1. New Features
1.1 3.8-0
1.1.1 SCP and Libraries
- BREAK, NOBREAK, and SHOW BREAK with no argument will set, clear, and
show (respectively) a breakpoint at the current PC.
1.2 GRI
- Added support for the GRI-99 processor.
1.3 HP2100
- Added support for the BACI terminal interface.
- Added support for RTE OS/VMA/EMA, SIGNAL, VIS firmware extensions.
1.4 Nova
- Added support for 64KW memory (implemented in third-party CPU's).
1.5 PDP-11
- Added support for DC11, RC11, KE11A, KG11A.
- Added modem control support for DL11.
- Added ASCII character support for all 8b devices.
2. Bugs Fixed
Please see the revision history on http://simh.trailing-edge.com or
in the source module sim_rev.h.
