No. All Unibus IO is initiated by PIREX, the 11 IO executive. It is
transferred, byte-by-byte or word-by-word, to/from buffers in the common
shared memory. So, for example, to print to the LP11:
1) PDP-15 sets up a properly formatted 8b byte-packed buffer in common
memory.
2) PDP-15 sets up a task control block (TCB) to print the buffer. The
TCB is also in common memory.
3) PDP-15 pokes the PDP-11 via the DR15-C, passing in the address of the
TCB.
4) PDP-11 invokes the LP11 "task" in PIREX, which pulls data from the
buffer and sends it to the printer.
5) At completion, the PDP-11 posts an API interrupt back to the PDP-15
via one of the two DR11-C's.
/Bob
On 3/17/2015 11:42 AM, Mark Pizzolato - Info Comm wrote:
On Monday, March 16, 2015 at 2:19 PM, Bob Supnik wrote:
This has been on the wish list for a decade.
The 15/76 Unichannel was a big PDP-15 that used a PDP-11/05 as an IO
processor to get access to inexpensive Unibus peripherals, particularly
the RK11-E/RK05, which supported 18b data, the LP11, the CR11, and
various plotters (not supported in SimH). XVM/DOS and XVM/RSX supported
the Unichannel, and standard DOS probably did as well.
The 15 and the 11 are crosscoupled through shared memory. Except for
4K-12K(W) of local memory, all of Unibus address space is mapped into
the 15's main memory. DMA transfers from the RK11-E could transfer 18b
data (using the Unibus parity lines for extra data lines); programmed IO
transfers from the IO processor transferred 16b data, zeroing out bits
0-1 on the 15.
Control is done by a DR15-C parallel interface cross-connected to two
DR11-C's in the 11. The 15 created task blocks in shared memory and
transfers an 18b pointer to the 11 via the DR15/11 parallel connection.
The 11's IO program, called PIREX, executes the directive and sends an
API interrupt back when done.
Clearly the DR15/11 paradigm passing through PIREX is necessary for DMA
devices, but how is programmed I/O handled.
With the whole Unibus space addressable from the 15 side, is there code on the
15 which actually does programmed I/O directly to the Unibus devices? If
programmed I/O is done directly by the 15, then this whole problem is very
different than one which relates to shared memory access.
- Mark
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