Re: Serial port programming

[chriswareham%chriswareham.demon.co.uk@localhost]

bqt%softjar.se@localhost wrote:
> I don't get it.
> 
> First of all, what do you mean by "the note sounding in the two stop bits"?
> 

I'm sort of thinking ahead to what would happen if this was a full blown
sequencer, and also interpreting what the manual says. If I was feeding the
drum machine a stream of bytes, then I would have to send a minimum of two stop
bits before the next note that sounds on the same beat. MIDI is similar in that
it's a serial protocol, so notes on the same beat (a chord for instance) are
really arpeggiated.

> Second. Yes, it should be perfectly fine hardware wise. RS-232 haven't 
> changed since 1983. If it was ok then, it is ok now.
> 

Cool, that's good to know.

> 
> Third. You describe the format of the serial data as start, 8 data bits, 
> two stop bits. And yet, in your program you explicitly sets the port to 
> one stop bit.
> 

This is where my understanding of the termios structure is lacking I guess!
I assume I should lose the ~CSTOPB, and it defaults to two stop bits?

> Maybe you should think a little more on what you are doing, and what you 
> want to do? :-)
> 

The intention so far was to prove I could send a single note - I only got the
drum machine yesterday, and only built cable a few hours ago! Thinking ahead is
definitely the next step!

>       Johnny
> 
> chriswareham%chriswareham.demon.co.uk@localhost wrote:
> > I've a few questions on serial port programming that I'm hoping people
> > may be able to help out with ...
> > 
> > I'm currently writing a program to control an old drum machine via my
> > computer's RS-232 serial port. On the drum machine end of the cable
> > there's a phono socket that accepts serial output and ground
> > connections. On the computer end, the request to send and clear to send
> > pins are connected together, as are the data set ready and data terminal
> > ready pins.
> > 
> > My first question, is whether connecting together the pins as I describe
> > above is still a viable option (the drum machine manual describes this
> > approach, but it dates from 1983).
> > 
> > The data format is described in the manual as follows:
> > 
> >            Start  LSB    1     2     3     4     5     6     7   2 stop bits
> > +12v      +-----+     +-----+     +-----+     +-----+     +-----+
> >           |     |     |     |     |     |     |     |     |     |
> >           |     |     |     |     |     |     |     |     |     |
> > -12v -----+     +-----+     +-----+     +-----+     +-----+     +-----+-----
> > 
> > The first four bits are the volume, and the second four bits are the
> > instrument, with the note sounding in the 2 stop bits. I wrote the
> > following code to try play a sound, and it sort of works - a snare drum
> > is played, but sometimes it's followed by other sounds. Even after I've
> > closed the connection, the odd sound still plays occasionally, but not
> > between me putting the drum machine into receive mode and running the
> > program the first time.
> > 
> > (drumulator.h)
> > 
> > #ifndef DRUMULATOR_H
> > #define DRUMULATOR_H
> > 
> > #define SERIAL_PORT "/dev/tty00"
> > 
> > #define CLAVE           0x0
> > #define COWBELL         0x1
> > #define CLAPS           0x2
> > #define OPEN_HI_HAT     0x3
> > #define CLOSED_HI_HAT   0x4
> > #define RIDE_CYMBAL     0x5
> > #define BASS_DRUM       0x6
> > #define SNARE_DRUM      0x7
> > #define RIMSHOT         0x8
> > #define HI_TOM          0x9
> > #define MID_TOM         0xA
> > #define LOW_TOM         0xB
> > #define METRONOME_CLICK 0xC
> > 
> > #define NOTE(vol, snd) (((vol) << 4) | (snd))
> > 
> > #endif
> > 
> > (drumulator.c)
> > 
> > #include <sys/types.h>
> > #include <sys/stat.h>
> > #include <errno.h>
> > #include <fcntl.h>
> > #include <stdio.h>
> > #include <string.h>
> > #include <termios.h>
> > #include <unistd.h>
> > 
> > #include "drumulator.h"
> > 
> > int
> > main(int argc, char *argv[])
> > {
> >     int fd, n;
> >     char buf[1];
> >     struct termios attr;
> > 
> >     fd = open(SERIAL_PORT, O_WRONLY | O_NOCTTY | O_NDELAY);
> > 
> >     if (fd < 0) {
> >         fprintf(stderr, "failed to open port: %sn", strerror(errno));
> >         return 1;
> >     }
> > 
> >     fcntl(fd, F_SETFL, 0);
> > 
> >     tcgetattr(fd, &attr);
> > 
> >     attr.c_cflag |= (CLOCAL | CREAD);
> >     attr.c_cflag &= ~PARENB;
> >     attr.c_cflag &= ~CSTOPB;
> >     attr.c_cflag &= ~CSIZE;
> >     attr.c_cflag |= CS8;
> > 
> >     cfsetospeed(&attr, B9600);
> > 
> >     tcsetattr(fd, TCSANOW, &attr);
> > 
> >     buf[0] = NOTE(0xF, SNARE_DRUM);
> > 
> >     n = write(fd, buf, 1);
> > 
> >     if (n < 0)
> >         fprintf(stderr, "failed to write to port: %sn", strerror(errno));
> > 
> >     close(fd);
> > 
> >     return 0;
> > }
> > 
> > So, my second question is whether I'm doing anything obviously wrong in
> > the code, and what problems might be causing the spurious notes (over
> > sensitivity of the drum machine serial interface for instance).
> > 
> > Finally, (and thanks if you've read this far!), I'd like to knock
> > together a primitive sequencer for the drum machine if I can resolve the
> > existing problems. Any suggestions on how to do the timing
> > (nanosleep(2)?) and to correctly allwo for the start and stop bits would
> > be most appreciated!
> > 
> > Chris
> > 
> > 
> 
>