verilator/uart-verilator.h

   1 // Copyright (C) IBM 2019, see LICENSE.CC4
   2 // based on code from microwatt https://github.com/antonblanchard/microwatt
   3
   4 /*
   5  * Our UART uses 16x oversampling, so at 50 MHz and 115200 baud
   6  * each sample is: 50000000/(115200*16) = 27 clock cycles. This
   7  * means each bit is off by 0.47% so for 8 bits plus a start and
   8  * stop bit the errors add to be 4.7%.
   9  */
  10
  11 enum state {
  12     IDLE, START_BIT, BITS, STOP_BIT, ERROR
  13 };
  14
  15 struct uart_tx_state {
  16     double error = 0.05;
  17
  18     enum state tx_state = IDLE;
  19     unsigned long tx_countbits;
  20     unsigned char tx_bits;
  21     unsigned char tx_byte;
  22     unsigned char tx_prev;
  23
  24     enum state rx_state = IDLE;
  25     unsigned char rx_char;
  26     unsigned long rx_countbits;
  27     unsigned char rx_bit;
  28     unsigned char rx = 1;
  29 };
  30
  31 void uart_tx(unsigned char tx);
  32 unsigned char uart_rx(void);
  33 struct uart_tx_state * uart_get_state(void);
  34 void uart_restore(struct uart_tx_state *);
  35