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bootloader in C

Hi there,

I've got a little problem while working on a bootloader for a C164 microcontroller. The microcontroller gets the data over the serial port. I've already implemented some functions that transmit some vmc and hex files to the controller while there is a OS running on it. But now I'd like to transmit my one bootstrap loader and I've got some problems with the serial communication in C.

Here's my code to configure the serial port under linux (I'm working on Suse Linux prof. 9.0):

int openport(char* device) {         int fd;         struct termios *current;                //IO-Settings         struct termios options;

        fd = open(device, O_RDWR | O_NOCTTY);         if (fd == -1)                 return -1;         bzero(&options, sizeof(options));

        tcgetattr(fd, &options);

        cfsetispeed(&options, B19200);         cfsetospeed(&options, B19200);                  options.c_cflag = B19200 | CRTSCTS | CSTOPB | CLOCAL | CREAD;         //8 databits, no paritybit, 1 stopbit         options.c_cflag &= ~PARENB;         options.c_cflag &= ~CSTOPB;         options.c_cflag &= ~CSIZE;         options.c_cflag |= CS8;         options.c_iflag = IGNPAR;         options.c_oflag = 0;         options.c_lflag = 0;         tcflush(fd, TCIFLUSH);         tcsetattr(fd, TCSANOW, &options);         return (fd); }

And now I simply want to transmit a zero byte (say 1 startbit, 8 zero bits and 1 stopbit):

int comport = openport("/dev/ttyS0"); write(comport,0,1); usleep(250); unsigned char cbuf = 0; while(read(sfd, &cbuf, 1)>0) {         printf("%i\t",(int) cbuf); }

but the microcontroller doesn't answer. It should return an identification byte, but I do not receive anything at all. I've got some software for windows that works fine (but only under windows) and I spied on its communication between itself and the comport and got this as the first two lines:

#00             //out   - zero byte #F8#D5          //in    - identification byte

So there can't be a failure at the microcontroller.

Thanks for any help.

Thomas

Reply to
Thomas Baier
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Hmmm, I tried /dev/ttys0 and got an error while writing, so I think I should use /dev/ttyS0 instead. I also tried /dev/cua0, but that doesn't work, too. What I expected as I found out that /dev/ttyS0 and /dev/cua0 should be the same device, aren't they? What exactly is DTR? I google a bit and found out that "the DTR signal is generated by your workstation and tells the computer or device on the other end that you are ready (a space voltage) or not-ready (a mark voltage). DTR is usually enabled automatically whenever you open the serial interface on the workstation." What does that mean for me? How can I find out if my microcontroller does have a full set of control lines? But wouldn't all the other thinks (like transferring hex and vm-codes to an existing OS) I'm already able to do work, if that is the problem?

@Gary:

What exactly looks suspicious at this line? How to do it in the correct way? I tried unsigned char handshake = 0; int ret = write(sfd,&handshake,1); but that doesn't work, too and as I think it is really the same, isn't it?

Thanks for your help

Thomas

Reply to
Thomas Baier

should

too.

other

DTR

Serial communications are always fun &-). DTR is "Data Terminal Ready". Devices like modems can be configured to assert DTR when they answer a call. On Linux systems, attempts to open /dev/ttyS? will only complete the open when DTR is asserted (they "hang" until then). Using /dev/cua0 allows a program to open a serial line without considering the state of DTR.

Not sure what development board you are using but many microcontroller development systems only have three wires: Rx, Tx and ground. If this is the case then you don't want the CRTSCTS option set when you open the serial port either (make sure that you clear that option).

way? The data buffer pointer is NULL, you are not sending a zero byte to your microcontroller. I don't know what is *at* location zero ('*0') in your (Linux) system but it may not be zero. You may even get an exception/signal.

Not the same but correct.

Andrew

Reply to
Andrew Jackson

Look back in C.A.E a few months for my example on how to really set termios to raw.

--
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Creepy, Soulless Gigolo for President ? NOT !
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THK is one weird, weird something.
Reply to
Bryan Hackney

Thomas

formatting link

may be helpful to you.

Andrew

Reply to
Andrew Jackson

Nope. PC's are "data terminals": they control DTR and read DSR. Modems are "data sets": they control DSR (usually asserted on power-up) and read DTR.

[Again, assuming you mean DSR.]

Not true. I just opened /dev/ttyS0 and it had DSR inactive:

$ ./showmodem.py /dev/ttyS0 DTR:1 DSR:0 RTS:1 CTS:0 CD:0 RI:0

DTR is active, but that's because DTR is an _output_ and is asserted during the open().

Use of the "cua" devices has been deprecated for many years, and they aren't even present on modern installations. If they're there, they're probably identical to the the ttyS devices. I'm not even sure there is a way to make an open() call block waiting for DSR.

IIRC, if the CLOCAL flag is not set, read() and write() will block waiting for CD.

IIRC, /dev/ttysN and /dev/ttycuN devices _used_ to block if the other one was in use, and an open() on /dev/ttys used to block waiting for CD.

--
Grant Edwards                   grante             Yow!  I feel real
                                  at               SOPHISTICATED being in
                               visi.com            FRANCE!
Reply to
Grant Edwards

Mea culpa: I was thinking of the system connected seeing DCD being asserted which is really DSR on the modem.

That's what I understand too. I have some code from '94 which fiddles with CLOCAL to open and write without waiting for CD.

You also used to be able to take a lock on the port by creating a magic file but that maybe showing my age ( which is also why I referred to /dev/ttys0 and /dev/ttyS0 :-) ).

Andrew

Reply to
Andrew Jackson

Well, it was the CRTSCTS option that causes my problem. So I cut it out and now everything works fine.

Thanks for your help

Thomas

Reply to
Thomas Baier

No, DCD on the PC is is DCD on the modem. It's an output from the data set and an input to the data terminal. DCD, DSR and DTR are three different signals.

There still is a convention of applications creating lock files under /var/lock for mutually exclusive access to serial ports.

--
Grant Edwards                   grante             Yow!  How many retired
                                  at               bricklayers from FLORIDA
                               visi.com            are out purchasing PENCIL
                                                   SHARPENERS right NOW??
Reply to
Grant Edwards

Well, what Grant said is correct. I only use C for the routines on my PC to transfer my assembler routines to the microcontroller. And if you haven't read my POST from yesterday, I'd like to say it again: IT WORKS!!! :-) And thanks again for your help on finding my mistake.

Greetings

Thomas

Reply to
Thomas Baier

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