works, but license issues due to bcm2835 lib

pyserialext/writec.c

@@ -0,0 +1,31 @@
+#include <unistd.h>
+#include <termios.h>
+#include <sys/ioctl.h>
+#include <stdio.h>
+#include <linux/serial.h>
+#include <errno.h>
+#include <string.h>
+#include <stdint.h>
+#include <bcm2835.h>
+
+
+const uint8_t DE_PIN = RPI_V2_GPIO_P1_11;
+
+int set_rs485_mode(int fd) {
+  bcm2835_init();
+  bcm2835_gpio_fsel(DE_PIN, BCM2835_GPIO_FSEL_OUTP);
+  bcm2835_gpio_write(DE_PIN, LOW);
+}
+
+ssize_t writec(int fd, char *buf, size_t count) {
+  bcm2835_gpio_write(DE_PIN, LOW);
+  ssize_t r = write(fd, buf, count);
+  uint8_t lsr;
+  do {
+    int r = ioctl(fd, TIOCSERGETLSR, &lsr);
+  } while (!(lsr & TIOCSER_TEMT));
+  bcm2835_gpio_write(DE_PIN, HIGH);
+
+  return r;
+}
+