1 // uart_a64.cc
2 // Allwinner A64 UART (16550)
3 
4 
5 #include <hw.h>
6 #include <uart.h>
7 #include <uart16550.h>
8 
9 
10 namespace Board {
11 namespace Uart {
12 
13 
14 namespace {
15 
16 constexpr uintptr_t UART0_BASE = 0x01c28000;
17 
18 constexpr auto SERIAL_CLOCK = 24000000;
19 constexpr auto BAUDRATE = 115200;
20 constexpr auto BAUDRATE_DIVISOR = (BAUDRATE * 16);
21 constexpr auto CLOCK_DIVISOR = (SERIAL_CLOCK + (BAUDRATE_DIVISOR / 2)) / BAUDRATE_DIVISOR;
22 
23 static_assert(CLOCK_DIVISOR == 13, "Should be 13");
24 
25 template <typename T>
26 uint8_t read8()
27 {
28     return Hw::read8(UART0_BASE + T::OFFSET);
29 }
30 
31 template <typename T>
32 T read()
33 {
34     return T{read8<T>()};
35 }
36 
37 
38 template <typename T>
39 void write8(uint8_t nValue)
40 {
41     Hw::write8(UART0_BASE + T::OFFSET, nValue);
42 }
43 
44 template <typename T>
45 void write(T Register)
46 {
47     write8<T>(Register.m_u.m_nValue);
48 }
49 
50 
51 } // anonymous namespace
52 
53 
54 void initialize()
55 {
56     for (; ; )
57     {
58         const auto LineStatusRegister{read<Uart16550::LineStatusRegister>()};
59         if (LineStatusRegister.m_u.m_Bits.m_TransmitterEmpty)
60             break;
61     }
62 
63     write(Uart16550::InterruptEnableRegister{});
64 
65     Uart16550::ModemControlRegister ModemControlRegister;
66     ModemControlRegister.m_u.m_Bits.m_DataTerminalReady = 1;
67     ModemControlRegister.m_u.m_Bits.m_RequestToSend = 1;
68     write(ModemControlRegister);
69 
70     Uart16550::FifoControlRegister FifoControlRegister;
71     FifoControlRegister.m_u.m_Bits.m_EnableFifos = 1;
72     FifoControlRegister.m_u.m_Bits.m_RcvrFifoReset = 1;
73     FifoControlRegister.m_u.m_Bits.m_XmitFifoReset = 1;
74     write(FifoControlRegister);
75 
76     Uart16550::LineControlRegister LineControlRegister;
77     LineControlRegister.m_u.m_Bits.m_DataLengthSelect = Uart16550::LineControlRegister::BITS_8;
78     write(LineControlRegister);
79 
80     LineControlRegister.m_u.m_Bits.m_DivisorLatchAccess = 1;
81     write(LineControlRegister);
82 
83     write8<Uart16550::DivisorLatchLowRegister>(CLOCK_DIVISOR & 0xff);
84     write8<Uart16550::DivisorLatchHighRegister>((CLOCK_DIVISOR >> 8) & 0xff);
85 
86     LineControlRegister.m_u.m_Bits.m_DivisorLatchAccess = 0;
87     write(LineControlRegister);
88 }
89 
90 
91 void send(uint8_t nValue)
92 {
93     for (; ; )
94     {
95         const auto LineStatusRegister{read<Uart16550::LineStatusRegister>()};
96         if (LineStatusRegister.m_u.m_Bits.m_TxHoldingRegisterEmpty)
97             break;
98     }
99     write8<Uart16550::TransmitHoldingRegister>(nValue);
100 }
101 
102 
103 uint8_t recv()
104 {
105     for (; ; )
106     {
107         const auto LineStatusRegister{read<Uart16550::LineStatusRegister>()};
108         if (LineStatusRegister.m_u.m_Bits.m_DataReady)
109             break;
110     }
111     return read8<Uart16550::ReceiveBufferRegister>();
112 }
113 
114 
115 } // namespace Uart
116 } // namespace Board