$ tail -11 uart.zig
    pub const txdata = packed struct {
        data: u8,
        _: u23 = undefined,
        full: bool,
    };

    pub fn isTxFull(self: Uart) bool {
        const data: u32 = self.readWord(UART_REG_TXFIFO);
        return @bitCast(txdata, data).full;
    }
};
$ zig build
./uart.zig:94:25: error: destination type 'uart.txdata' has size 5 but source type 'u32' has size 4
        return @bitCast(txdata, data).full;
                        ^
./uart.zig:94:33: note: referenced here
        return @bitCast(txdata, data).full;
                                ^
main...The following command exited with error code 1:
/usr/bin/zig build-exe /home/soeren/src/zig-riscv-embedded/main.zig --c-source /home/soeren/src/zig-riscv-embedded/start.S --c-source /home/soeren/src/zig-riscv-embedded/irq.S --cache-dir /home/soeren/src/zig-riscv-embedded/zig-cache --name main -target riscv32-freestanding-none --linker-script /home/soeren/src/zig-riscv-embedded/fe310_g000.ld --cache on 

Build failed. The following command failed:
/home/soeren/src/zig-riscv-embedded/zig-cache/o/XGC2fiFbipnsx-HIJUdkhjxvn-PfH7gtnaesPV0HuQhOZJtUE3yZ26YoDIyjjLyT/build /usr/bin/zig /home/soeren/src/zig-riscv-embedded /home/soeren/src/zig-riscv-embedded/zig-cache