HelenOS sources

chardev_putuchar  109 uspace/srv/hid/output/port/chardev.c 		chardev_putuchar(*p++);
chardev_putuchar  215 uspace/srv/hid/output/port/chardev.c 	serial_init(chardev_putuchar, chardev_control_puts, chardev_flush);
HelenOS homepage, sources at GitHub