I know this refers to the 5 bit topic, however I'm wondering if changing from 5 bits only would assist in reading DCD:

"Many USB serial ports do not support a 5 bits per byte configuration however when
configuring a serial port under DOS it is fairly common practice to simply set the
serial ports LCR register to 0x80 to set the DLAB bit before setting the LCR to the
actually desired value. This patch is a hack to work around the problem with these
adapters at the cost of disabling the 9600 baud 5.N,1 configuration."
http://sourceforge.net/p/dosbox/patches/249/

I see the some people have installed a real DOS in DOSBox such as M$DOS.

Obviously this cannot change the emulated COM port hardware, however would it not bypass some of the DOSBox code that talks to the emulated hardware?

Then the question is which DOS? PCDOS, DRDOS, FREEDOS? Perhaps one was better suited to software which relied on COM ports, such as BBS's?

I have now tried adjusting the cycles with no change, from as low as 50 up to 3500.

I am also going to try the Megabuild fork: http://home.arcor.de/h-a-l-9000/megabuild.html

I also ran two DOS serial port tools (ports.exe and mdr.exe) and both readily found a 16550A at 2f8 / IRQ3... I wonder if the 16550A FIFO buffer is affecting DCD?

I doubt this will help, but you may also try vDos as another build where people worked with compatibility.

Would PCem perhaps be a better option?

mr_bigmouth_502 wrote:

Would PCem perhaps be a better option?

Unless I'm mistaken, PCem it won't run on ARM processors, like the one in my Raspberry Pi which runs DOSBox perfectly, except for my DCD assertion detection issue...

Tertz wrote:

I doubt this will help, but you may also try vDos as another build where people worked with compatibility.

I believe that VDos is for Windows only I.e. It won't run on my Rasperry Pi which I'm using for DOSBox.

https://www.vdos.info

IBM Portable PC wrote:

It won't run on my Rasperry Pi which I'm using for DOSBox.

VDos is open sourced and has port to OSX. Maybe there is or may be done a port for your case.

Well, I've been back on this issue and decided to take a look at the serial port code. I am not into C (yet) however, I can see that the DCD bit of the emulated 16550UART is at least considered,.. however it does not work for me.

/*****************************************************************************/
/* Modem Status Register (r) **/
/*****************************************************************************/
// Contains status of the control input lines (CD, RI, DSR, CTS) and
// their "deltas": if level changed since last read delta = 1.
// modified by:
// - real values
// - write operation to MCR in loopback mode
Bitu CSerial::Read_MSR () {
Bit8u retval=0;

if (loopback) {

if (rts) retval |= MSR_CTS_MASK;
if (dtr) retval |= MSR_DSR_MASK;
if (op1) retval |= MSR_RI_MASK;
if (op2) retval |= MSR_CD_MASK;

} else {

updateMSR();
if (cd) retval |= MSR_CD_MASK;
if (ri) retval |= MSR_RI_MASK;
if (dsr) retval |= MSR_DSR_MASK;
if (cts) retval |= MSR_CTS_MASK;

}
// new delta flags
if(d_cd) retval|=MSR_dCD_MASK;
if(d_ri) retval|=MSR_dRI_MASK;
if(d_cts) retval|=MSR_dCTS_MASK;
if(d_dsr) retval|=MSR_dDSR_MASK;

d_cd = false;
d_ri = false;
d_cts = false;
d_dsr = false;

clear (MSR_PRIORITY);
return retval;
http://sourceforge.net/p/dosbox/code-0/3843/t … alport.cpp#l837

I am still considering the Megabuilds fork, however I am lead to believe that compiling on Raspbian is an issue..

I have just loaded Megabuild on my Mac and can report that it DOES detect CD assertions correctly! 😀

I have some sort of timing issue, however I'm yet to adjust cycles etc and if successful, then I need to compile Megabuild in Raspbian...