Re: Audio "click" during knob rotation


jerry@tr2.com
 

Sharc? Whazzat? IIRC the DSP we were using was a TMS320C31. We didn't
use any of the DSP features, it was just a good cheap CPU.

They sent me to a 1-week seminar to learn about it. In the class on
assembly language I remarked - "Of course, all real programming is done in
C". Ironically, I wound up doing my project in ASM.

Another cool thing I got to do - this was around 1987 - was to write
a program that converted a Compaq 286 into a recording oscilloscope.
That one really brought home the power of circular buffers - sized to a
power of 2. The CPU had segment registers, and each segment was max 64K.
In my sample-gathering interrupt routine, I used a 64K circular buffer.
That got me the wraparound for free - 0xffff + 1 = 0. Also - zero minus one
= 0xffff.

- Jerry

On 2021-06-23 11:29, Julian N4JO wrote:
Thanks for that story, Jerry. I know exactly where you're coming from
on the subject of optimization.
My story (and I'm not going to try to one-up you!) also includes
assembly language programming - 8086/87. It was a machine tool control
project that brought me over here to the 'States in 1982 for my
employer, Gettys Mfg., who made servo motors and drives, and a strange
control system called a "tracer/duplicator" which, when attached to a
milling machine, would copy models into real metal by means of tracing
over the model with a probe, and controlling servos to move a milling
cutter over a raw metal blank. Obviously we were eventually replaced
with CNC, but in our heyday our system was used extensively in the
automotive industry centered around Detroit/Windsor. and throughout UK
and Europe.
The project was canceled in '83 when the company was bought out, I
stayed here anyway; offshoot company started by original team to
continue the work; I rejoined that team in '89 I think it was, some
years after I'd earned my Green Card in '85, and I got involved with
the Mk II version, which is where the fun - and my story - starts.
I had to add a lot of extra features (including adding real CNC
capability), so I nailed all our existing code into a C framework. To
do that I had to remap the register usage and function call structure
to match the method the compiler used; quite a task, but at the end of
the day I could now write new C functions to be called from the
assembly language code under the C framework!
But yes, there was a lot of optimization to do. Our processor
complement increased from 2 x 8086/87 to 3x 286/287 on Intel Multibus
I, which was not much of an improvement because of bus/shared memory
access constraints. The REAL boost came when we graduated to a pair of
486DX, which had the math co-processor built in. That reduced the time
for the math co-pro context switch down from some 93 processor cycles
to just a handful. Given the amount of floating point math we need
(two and three dimensional trig), that made a heckuva difference. I
reduced our mainline interrupt loop time from 10ms down to 1.25 ms if
I recall, and the beast was still begging for more work to do!
Fun times.
Was your TI DSP the Sharc? I did some work on that while I was
software manager at Tech 80, up here in Minneapolis. We got bought out
and things went south, but it was fun while it lasted. --
Julian, N4JO.
Links:
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[1] https://groups.io/g/QRPLabs/message/67672
[2] https://groups.io/mt/83622776/243852
[3] https://groups.io/g/QRPLabs/post
[4] https://groups.io/g/QRPLabs/editsub/243852
[5] https://groups.io/g/QRPLabs/leave/10312280/243852/1190336630/xyzzy

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