cc3200/mods/pybuart: Implement uart.flush() and uart.txdone().

uart.flush()

flush() will wait until all characters have been sent.
To avoid a permanent lock, a timeout applies depending on the
size of FIFO and the baud rate.

ret = uart.txdone()

ret is True if no transfer is in progress.
ret is False otherwise.

ports/cc3200/mods/pybuart.c

@@ -66,6 +66,7 @@
 #define PYBUART_TX_MAX_TIMEOUT_MS               (5)
 
 #define PYBUART_RX_BUFFER_LEN                   (256)
+#define PYBUART_TX_BUFFER_LEN                   (17)
 
 // interrupt triggers
 #define UART_TRIGGER_RX_ANY                     (0x01)
@@ -558,6 +559,17 @@ invalid_args:
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_KW(pyb_uart_irq_obj, 1, pyb_uart_irq);
 
+STATIC mp_obj_t machine_uart_txdone(mp_obj_t self_in) {
+    pyb_uart_obj_t *self = MP_OBJ_TO_PTR(self_in);
+
+    if (MAP_UARTBusy(self->reg) == false) {
+        return mp_const_true;
+    } else {
+        return mp_const_false;
+    }
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(machine_uart_txdone_obj, machine_uart_txdone);
+
 STATIC const mp_rom_map_elem_t pyb_uart_locals_dict_table[] = {
     // instance methods
     { MP_ROM_QSTR(MP_QSTR_init),        MP_ROM_PTR(&pyb_uart_init_obj) },
@@ -565,6 +577,7 @@ STATIC const mp_rom_map_elem_t pyb_uart_locals_dict_table[] = {
     { MP_ROM_QSTR(MP_QSTR_any),         MP_ROM_PTR(&pyb_uart_any_obj) },
     { MP_ROM_QSTR(MP_QSTR_sendbreak),   MP_ROM_PTR(&pyb_uart_sendbreak_obj) },
     { MP_ROM_QSTR(MP_QSTR_irq),         MP_ROM_PTR(&pyb_uart_irq_obj) },
+    { MP_ROM_QSTR(MP_QSTR_txdone),      MP_ROM_PTR(&machine_uart_txdone_obj) },
 
     /// \method read([nbytes])
     { MP_ROM_QSTR(MP_QSTR_read),        MP_ROM_PTR(&mp_stream_read_obj) },
@@ -574,6 +587,7 @@ STATIC const mp_rom_map_elem_t pyb_uart_locals_dict_table[] = {
     { MP_ROM_QSTR(MP_QSTR_readinto),    MP_ROM_PTR(&mp_stream_readinto_obj) },
     /// \method write(buf)
     { MP_ROM_QSTR(MP_QSTR_write),       MP_ROM_PTR(&mp_stream_write_obj) },
+    { MP_ROM_QSTR(MP_QSTR_flush),       MP_ROM_PTR(&mp_stream_flush_obj) },
 
     // class constants
     { MP_ROM_QSTR(MP_QSTR_RX_ANY),      MP_ROM_INT(UART_TRIGGER_RX_ANY) },
@@ -635,6 +649,21 @@ STATIC mp_uint_t pyb_uart_ioctl(mp_obj_t self_in, mp_uint_t request, mp_uint_t a
         if ((flags & MP_STREAM_POLL_WR) && MAP_UARTSpaceAvail(self->reg)) {
             ret |= MP_STREAM_POLL_WR;
         }
+    } else if (request == MP_STREAM_FLUSH) {
+        // The timeout is estimated using the buffer size and the baudrate.
+        // Take the worst case assumptions at 13 bit symbol size times 2.
+        uint64_t timeout = mp_hal_ticks_ms()  +
+            (PYBUART_TX_BUFFER_LEN) * 13000 * 2 / self->baudrate;
+
+        do {
+            if (machine_uart_txdone((mp_obj_t)self) == mp_const_true) {
+                return 0;
+            }
+            MICROPY_EVENT_POLL_HOOK
+        } while (mp_hal_ticks_ms() < timeout);
+
+        *errcode = MP_ETIMEDOUT;
+        ret = MP_STREAM_ERROR;;
     } else {
         *errcode = MP_EINVAL;
         ret = MP_STREAM_ERROR;