Posted on May 17, 2011 at 14:28
After some research and assistance from ST Support (thanks Jiri), I have determined a solution to part (2) - detecting whether the host port is open.
Conventionally, when a port is opened the DTR modem control line is asserted. This information is passed to a CDC class device, so I can use this to achieve my aim. It is possible for an application to change the behaviour of DTR, but this should not happen in any of the client applications that are likely to connect to this device in this case. However there is a back-up plan that implicitly assumes the port to be open if the line-coding (baud, framing) are set. In this case there is no means of detecting closure but at least it will not prevent an unconventional application from working with my device, even if it then causes it to crash when it disconnects.
Regarding ST's VCP example code specifically I have made the following changes to usb_prop.c:
1) Added the following function:
#include <stdbool.h>
static bool host_port_open = false ;
bool Virtual_Com_Port_IsHostPortOpen()
{
return bDeviceState == CONFIGURED && host_port_open ;
}
2) Modified Virtual_Com_Port_NoData_Setup() handling of SET_CONTROL_LINE_STATE thus:
else if (RequestNo == SET_CONTROL_LINE_STATE)
{
// Test DTR state to determine if host port is open
host_port_open = (pInformation->USBwValues.bw.bb0 & 0x01) != 0 ;
return USB_SUCCESS;
}
3) To allow use with applications that do not operate DTR conventionally I have also modified Virtual_Com_Port_Data_Setup() handling of SET_LINE_CODING thus:
else if (RequestNo == SET_LINE_CODING)
{
if (Type_Recipient == (CLASS_REQUEST | INTERFACE_RECIPIENT))
{
CopyRoutine = Virtual_Com_Port_SetLineCoding;
// If line coding is set the port is implicitly open
// regardless of host's DTR control. Note: if this is
// the only indicator of port open, there will be no indication
// of closure, but this will at least allow applications that
// do not assert DTR to connect.
host_port_open = true ;
}
Request = SET_LINE_CODING;
}
