<dngrs (spookyvision@github)> old code:
#[task(binds = OTG_FS, local = [usb_dev, serial, rx], shared = [do_debug])]
    fn usb_tx(cx: usb_tx::Context) {
        let rx = cx.local.rx;
        let serial = cx.local.serial;
        if serial.dtr() {
            if let Ok(grant) = rx.read() {
                debug!("dtr & grant - draining queue");
                match serial.write(&grant) {
                    Ok(len) if len > 0 => {
                        debug!("wrote {} bytes", len);
                        grant.release(len);