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Implement usbser.sys workaround on Windows #154

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Implement usbser.sys workaround on Windows #154

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13 changes: 11 additions & 2 deletions src/windows/com.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,9 @@ pub struct COMPort {
handle: HANDLE,
timeout: Duration,
port_name: Option<String>,
// keeps track of DTR state so we can re-send DTR on RTS change to work
// around USB Serial driver misbehaviour
dtr: bool,
}

unsafe impl Send for COMPort {}
Expand Down Expand Up @@ -122,6 +125,7 @@ impl COMPort {
handle: cloned_handle,
port_name: self.port_name.clone(),
timeout: self.timeout,
dtr: self.dtr,
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This clones the dtr state when a COMPort is cloned, which might not always be the right behaviour.

Another option could be to remove the dtr field from this struct, and instead call DeviceIoControl with IOCTL_SERIAL_GET_DTRRTS in write_request_to_send to find the current state of the DTR pin, as described in this Stack Overflow answer. It's another potentially fallible syscall though, so I just went with this approach for now. Happy to make this change if desired however

})
} else {
Err(super::error::last_os_error())
Expand Down Expand Up @@ -152,6 +156,7 @@ impl COMPort {
handle: handle as HANDLE,
timeout: Duration::from_millis(100),
port_name: None,
dtr: false,
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I would do the call to DeviceIoControl here since we cannot assume the state. But if the call fails (which I would consider unlikely), the most sane option is to just panic as it means that the handle from FFI did something weird.

}
}
}
Expand Down Expand Up @@ -260,13 +265,17 @@ impl SerialPort for COMPort {

fn write_request_to_send(&mut self, level: bool) -> Result<()> {
if level {
self.escape_comm_function(SETRTS)
self.escape_comm_function(SETRTS)?;
} else {
self.escape_comm_function(CLRRTS)
self.escape_comm_function(CLRRTS)?;
}

self.write_data_terminal_ready(self.dtr)
}

fn write_data_terminal_ready(&mut self, level: bool) -> Result<()> {
self.dtr = level;

if level {
self.escape_comm_function(SETDTR)
} else {
Expand Down
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