Not working serial

uart.rs

#![no_std]
#![no_main]

use core::{fmt::Write as _, str::from_utf8};
use embedded_hal_nb::serial::{Read, Write};
use esp_backtrace as _;
use esp_hal::{
    clock::ClockControl,
    gpio,
    peripherals::Peripherals,
    prelude::*,
    uart::{self, Uart},
};
use esp_println::println;
use nb;


#[entry]
fn main() -> ! {
    let peripherals = Peripherals::take();
    let system = peripherals.SYSTEM.split();
    let clocks = ClockControl::max(system.clock_control).freeze();

    let io = gpio::IO::new(peripherals.GPIO, peripherals.IO_MUX);
    let pins = uart::TxRxPins::new_tx_rx(io.pins.gpio0, io.pins.gpio1);

    let mut uart = Uart::new_with_config(
        peripherals.UART0,
        uart::config::Config {
            baudrate: 115_200,
            data_bits: uart::config::DataBits::DataBits8,
            parity: uart::config::Parity::ParityNone,
            stop_bits: uart::config::StopBits::STOP1,
            ..Default::default()
        },
        Some(pins),
        &clocks,
        None,
    );

    loop {
        // Problem is on the next line
        while let Ok(byte) = nb::block!(uart.read()) {
            println!("{:?}", byte);
            writeln!(uart, "{}", from_utf8(&buf).unwrap()).unwrap();
            nb::block!(uart.flush()).unwrap();
        }
    }
}