uart: support TX

board/N4

@@ -147,3 +147,6 @@ output VGA_B7
 
 input PS2_CLK
 input PS2_DAT
+
+output UART_TX
+input  UART_RX

include/uart.h

@@ -7,9 +7,14 @@
 class UART : public Component{
 private:
   Term *term;
+  int state;
+  uint16_t divisor;
+  uint16_t divisor_cnt;
+  uint8_t data;
 public:
   UART(SDL_Renderer *rend, int cnt, int init_val, int ct, int x, int y, int w, int h);
   ~UART();
+  void set_divisor(uint16_t d);
 
   virtual void update_gui();
   virtual void update_state();

src/nvboard.cpp

@@ -1,6 +1,7 @@
 #include <nvboard.h>
 #include <keyboard.h>
 #include <vga.h>
+#include <uart.h>
 #include <sys/time.h>
 #include <stdarg.h>
 
@@ -36,6 +37,10 @@ void nvboard_update() {
   extern bool is_kb_idle;
   if (!is_kb_idle) kb->update_state();
 
+  extern UART* uart;
+  extern bool is_uart_idle;
+  if (!(is_uart_idle && pin_peek(UART_TX))) uart->update_state();
+
   static uint64_t last = 0;
   static uint32_t cpf = 0; // count per frame
   static uint32_t cnt = 0;

src/term.cpp

@@ -9,7 +9,6 @@ Term::Term(SDL_Renderer *r, int x, int y, int w, int h):
   w_in_char = region.w / 10;
   h_in_char = region.h / 16;
   uint8_t *l = new_line();
-  memset(l, 'a', w_in_char);
   cursor_texture = new_texture(r, 10, 16, 0x10, 0x10, 0x10);
 }
 

src/uart.cpp

@@ -2,9 +2,11 @@
 #include <uart.h>
 
 UART* uart = NULL;
+bool is_uart_idle = true;
 
 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) {
+    Component(rend, cnt, init_val, ct),
+    state(0), divisor(16), divisor_cnt(1) {
   term = new Term(rend, x, y, w, h);
 }
 
@@ -17,15 +19,33 @@ void UART::update_gui() {
 }
 
 void UART::update_state() {
-  static int i = 0;
-  i ++;
-  if (i < 10) return;
-  i = 0;
-  static uint8_t ch = ' ';
-  ch += 1;
-  if (ch == 128) ch = ' ';
-  term->feed_ch(ch);
-  update_gui();
+  if (divisor_cnt < divisor) {
+    divisor_cnt ++;
+    return;
+  }
+  divisor_cnt = 1;
+
+  uint8_t tx = pin_peek(UART_TX);
+  if (state == 0) { // idle
+    if (!tx) { // start bit
+      data = 0;
+      is_uart_idle = false;
+      state ++;
+    }
+  } else if (state >= 1 && state <= 8) { // data
+    data = (tx << 7) | (data >> 1);  // data bit
+    state ++;
+  } else if (state == 9) {
+    if (tx) {
+      term->feed_ch(data); update_gui();
+      state = 0;
+      is_uart_idle = true;
+    } // stop bit
+  }
+}
+
+void UART::set_divisor(uint16_t d) {
+  divisor = d;
 }
 
 void init_uart(SDL_Renderer *renderer) {