README.md
This driver is designed to support a DR-11W under
RSX-11M+ version 3.0 and later interfaced to an ACROAMATICS
2110 Telemetry data processor (TDP) system. The design of
this driver follows the VAX/VMS XA driver in direct memory
access (DMA) mode as closely as possible. This was done to
ease compatibility of software access to the telemetry sys-
tem, and its always nice to have a structure to follow.
The driver accepts 4 general functions, read logical
block, write logical block, set characteristics, and sense
characteristics. In addition, the read and write accept
subfunction codes reset, set function bits, and set time
out. The device is flagged as a record structured sequen-
tial device in the driver unit control block (UCB). This
has the side effect of allowing use of read/write virtual,
but the operating system will convert this to read/write
logical and strip off all subfunction bits.
The read and write logical functions are used to
transfer data via a dma channel between the external device
and the host PDP-11. The transfers can have either a reset
or set function subfunction as required, and a new time out
set if required. The processing of the subfunctions is per-
formed prior to setting up the DMA channel, which would al-
low for most hardware handshake protocols to be fulfilled.
The time out processing is performed just before setting the
go bit to start the transfer. The transfer complete is sig-
nalled by an interrupt, which can come from either a word
count register overflow or any of the exception interrupts.
The transfer complete is signalled by placing the number of
bytes transferred in the second word of the input output
status block (IOSB) and success (is.suc) in the first word
of the IOSB. A device time out will place a time out error
code (ie.tmo) in the frist word of the IOSB and the CSR in
the second word.
The driver allocates and releases unibus mapping regis-
ters (UMR's) for each data transfer. If a higher speed
transfer is required, the driver could be modified to accept
device allocation and permanently allocate UMR's at that
time. The interface to the TDP has a 4K word first in first
out (FIFO) buffer which allows extra processing time between
transfers before a data overrun will occur.
Since is is possible for rogue devices to generate
spurious interrupts, or as in this device's case, to
generate a DMA done interrupt coincident with a frame done
interrupt when the requested transfer count exactly equals a
telemetry frame. In this case, a hardware race will occur
in which the ATTENTION interrupt and the DMA done interrupt
will both be pending. To assure correct handling of all in-
terrupts, all transfers are flagged with an interrupt ex-
pected in the UCB and the interrupt handler clears the flag.
If an interrupt occurs when the flag is clear, the interrupt
is dismissed. All access to the interrupt expected flag is
done at hardware priority (PR5) to assure proper synchroni-
zation. All setting of the CSR is also done at device
priority to assure stability.
DR-11W DRIVER FOR RSX-11M+ version 3.0 OR LATER Page 2
For non-DMA operations, the sense and set characteris-
tics functions are available. For a Set characteristic
(io.stc) function, the user parameter (first word of the I/O
parameter block) has all but the lower three bits cleared,
and these bits are then left shifted to the control bit
positions and or'ed into the CSR. For a sense characteris-
tics, the CSR is merely read. In both cases the entire CSR
is returned in the second word of the IOSB. No interrupt
processing is expected with these functions, and should one
occur, it would be dismissed as an unexpected interrupt.
The following code fragments shows a typical MACRO-11
interface to the QA driver. The setting up of the subfunc-
tion codes is as follows:
DR-11W DRIVER FOR RSX-11M+ version 3.0 OR LATER Page 3
The read logical and set characteristics are are very
similar to the write logical and sense characteristic exam-
ples. The use of a new time out would be similar to the set
function subfunction, being or'ed into the function code,
and the new time out (in seconds) as the fourth element of
the device dependant parameters.
Two command files (asm.cmd and bld.cmd) are used to as-
semble and build the driver. These files assume the source
code is in the named directory [qadrv]. The driver map is
placed in UIC [1,34] and the driver and symbol table in UIC
[1,54]. The command file QA.CMD will load the driver at the
top of the GEN partition and configure online the controller
(QAA) and the unit (QA0).