uart: support RX

example/README.md

@@ -7,5 +7,6 @@
 1. 拨动右边的8个拨码开关, 可控制对应LED的亮灭
 1. 按下按钮可将8~12号中对应的LED亮灭效果取反
 1. 8个数码管流水显示数字0-7
-1. 窗口右侧为VGA输出, 将会展示一张图片
+1. 窗口左下角为VGA输出, 将会展示一张图片
+1. 窗口右侧中部为UART RX输入, 鼠标选中后可输入字符串, 按回车后字符串将通过UART RX端输入, 通过回环连接从UART TX端输出, 显示在右上方终端
 1. 敲击键盘, 终端将会输出按键的扫描码

example/constr/top.nxdc

@@ -22,3 +22,6 @@ seg7 (SEG7A, SEG7B, SEG7C, SEG7D, SEG7E, SEG7F, SEG7G, DEC7P)
 
 ps2_clk PS2_CLK
 ps2_data PS2_DAT
+
+uart_tx UART_TX
+uart_rx UART_RX

example/vsrc/top.v

@@ -5,6 +5,8 @@ module top(
     input [7:0] sw,
     input ps2_clk,
     input ps2_data,
+    input uart_rx,
+    output uart_tx,
     output [15:0] ledr,
     output VGA_CLK,
     output VGA_HSYNC,
@@ -77,6 +79,11 @@ vmem my_vmem(
     .vga_data(vga_data)
 );
 
+uart my_uart(
+  .tx(uart_tx),
+  .rx(uart_rx)
+);
+
 endmodule
 
 module vmem(

example/vsrc/uart.v

@@ -0,0 +1,6 @@
+module uart (
+  output tx,
+  input rx
+);
+  assign tx = rx;
+endmodule

include/uart.h

@@ -8,10 +8,11 @@
 class UART : public Component{
 private:
   Term *tx_term, *rx_term;
-  int state;
+  int tx_state, rx_state;
   uint16_t divisor;
-  uint8_t data;
+  uint8_t tx_data, rx_data;
   std::string rx_input;
+  std::string rx_sending_str;
   static constexpr const char *rx_input_prompt = "UART TX (Press Enter to issue): ";
   bool tx_update_gui, rx_update_gui;
   uint8_t *p_tx;
@@ -22,7 +23,8 @@ public:
 
   virtual void update_gui();
   virtual void update_state();
-  void tx_check();
+  void tx_receive();
+  void rx_send();
   void rx_getchar(uint8_t);
 };
 

src/nvboard.cpp

@@ -25,7 +25,10 @@ void nvboard_update() {
 
   extern UART* uart;
   extern int16_t uart_divisor_cnt;
-  if (unlikely((-- uart_divisor_cnt) < 0)) uart->tx_check();
+  if (unlikely((-- uart_divisor_cnt) < 0)) {
+    uart->tx_receive();
+    uart->rx_send();
+  }
 
   static uint64_t last = 0;
   static int cpf = 1; // count per frame

src/uart.cpp

@@ -10,7 +10,7 @@ int16_t uart_divisor_cnt = 0;
 
 UART::UART(SDL_Renderer *rend, int cnt, int init_val, int ct, int x, int y, int w, int h):
     Component(rend, cnt, init_val, ct),
-    state(0), divisor(16), tx_update_gui(false) {
+    tx_state(0), rx_state(0), divisor(16), tx_update_gui(false) {
   tx_term = new Term(rend, x, y, w, h);
   rx_term = new Term(rend, x, y + h, w, 20);
   uart_divisor_cnt = divisor - 1;
@@ -20,7 +20,9 @@ UART::UART(SDL_Renderer *rend, int cnt, int init_val, int ct, int x, int y, int
 
   rx_term->feed_str(rx_input_prompt);
   rx_input = "";
+  rx_sending_str = "";
   rx_update_gui = true;
+  pin_poke(UART_RX, 1);
 }
 
 UART::~UART() {
@@ -30,30 +32,48 @@ UART::~UART() {
 void UART::update_gui() { // everything is done in update_state()
 }
 
-void UART::tx_check() {
+void UART::tx_receive() {
   uart_divisor_cnt = divisor - 1;
 
   uint8_t tx = *p_tx;
-  if (state == 0) { // idle
+  if (tx_state == 0) { // idle
     if (!tx) { // start bit
-      data = 0;
-      state ++;
+      tx_data = 0;
+      tx_state ++;
     }
-  } else if (state >= 1 && state <= 8) { // data
-    data = (tx << 7) | (data >> 1);  // data bit
-    state ++;
-  } else if (state == 9) {
+  } else if (tx_state >= 1 && tx_state <= 8) { // data
+    tx_data = (tx << 7) | (tx_data >> 1);  // data bit
+    tx_state ++;
+  } else if (tx_state == 9) {
     if (tx) { // stop bit
-      state = 0;
-      tx_term->feed_ch(data);
+      tx_state = 0;
+      tx_term->feed_ch(tx_data);
       tx_update_gui = true;
     }
   }
 }
 
+void UART::rx_send() {
+  // the uart_divisor_cnt is maintained in tx_receive()
+  if (rx_state == 0) { // idle
+    rx_data = rx_sending_str[0];
+    if (rx_data == '\0') return;
+    rx_sending_str.erase(0, 1);
+    pin_poke(UART_RX, 0);  // start bit
+    rx_state ++;
+  } else if (rx_state >= 1 && rx_state <= 8) { // data
+    pin_poke(UART_RX, rx_data & 1);  // data bit
+    rx_data >>= 1;
+    rx_state ++;
+  } else if (rx_state == 9) {
+    pin_poke(UART_RX, 1);  // stop bit
+    rx_state = 0;
+  }
+}
+
 void UART::rx_getchar(uint8_t ch) {
   if (ch == '\n') {
-    printf("Get RX input = %s\n", rx_input.c_str());
+    rx_sending_str += rx_input;
     rx_term->clear();
     rx_term->feed_str(rx_input_prompt);
     rx_input = "";