serial_read does not work in VirtualBox

[mikijov]

This is likely not DOS-Serial-Library problem, but rather VirtualBox one; but I wanted to ask if anyone tried running the library in a virtual environment?

I have simple code:

#include "serial.h"

void test_dos_serial_library() {
   int err = serial_open(COM_1, 9600, 8, 'n', 1, SER_HANDSHAKING_NONE);
   if (err < 0) {
      fatal("ERROR: error opening serial port. (%d)", err);
   }

   while (true) {
      char ch;
      int err = serial_read(COM_1, &ch, 1);
      if (err < 0) {
         fatal("ERROR: error reading from serial port. (%d)", err);
      } else if (err > 0) {
         cprintf("%02X '%c'\n\r", ch, ch);
      }
      serial_debug();
      delay(100);
   }
}

and this code works fine on physical machine running FreeDOS 1.3. But when running in VirtualBox running DOS 6.22 it reads garbage.

To debug, I also used bios functions, and the code below actually works.

#include <bios.h>

void test_bios_serial() {
   uint16_t err = _bios_serialcom(_COM_INIT, 0, _COM_9600 | _COM_NOPARITY | _COM_CHR8 | _COM_STOP1);
   cprintf("%04X %016b\n\r", err, err);
   while (true) {
      err = _bios_serialcom(_COM_RECEIVE, 0, 0);
      if (err == 0x6000) {
         // do nothing
      } else if (err > 0xFF) {
         cprintf("%04X %016b\n\r", err, err);
      } else {
         cprintf("%02X '%c'\n\r", err, err);
      }
   }
}

I am using Watcom 2.0 and compiling for 8086:

CFLAGS=-bcl=dos -0 -d0 -wx -zc -q -ze @directives.lnk

serialhd.exe: serialhd.c serial.c
	wcl $^ -fe=$@ -fm=serialhd $(CFLAGS)

As much as I could debug the interrupt handler, it seems that inp() in line

DOS-Serial-Library/serial.c

Line 405 in 42987f6

data = UART_READ_DATA(com);

returns garbage. I replaced this with data='m' and I confirmed that I was reliably receiving 'm' from serial_read().

Long story short, just asking if there is anything that can be done to make this work in a virtual environment to ease my development?