Add SerialPort self-test to constructor

4 files changed, 28 insertions, 19 deletions

diff --git a/.clang-format b/.clang-format
index ec6cc2c..e490b56 100644
--- a/.clang-format
+++ b/.clang-format
@@ -2,6 +2,7 @@
 BasedOnStyle: Chromium
 ColumnLimit: '120'
 AccessModifierOffset: '-2'
-AllowShortBlocksOnASingleLine: true
+AllowShortIfStatementsOnASingleLine: true
+AllowShortLoopsOnASingleLine: true
 
 ...
diff --git a/drivers/serial.cc b/drivers/serial.cc
index 84dd4b0..22b8051 100644
--- a/drivers/serial.cc
+++ b/drivers/serial.cc
@@ -5,22 +5,18 @@
  * |dla|   | parity    | s | data  |
  */
 enum LineControlRegister : uint8_t {
-  // data bits
-  d5bit = 0b00000000,
+  d5bit = 0b00000000,  // data bits
   d6bit = 0b00000001,
   d7bit = 0b00000010,
   d8bit = 0b00000011,
-  // parity bits
-  none = 0b00000000,
+  none = 0b00000000,  // parity bits
   odd = 0b00001000,
   even = 0b00011000,
   mark = 0b00101000,
   space = 0b00111000,
-  // stop bits
-  s1bit = 0b00000000,
+  s1bit = 0b00000000,  // stop bits
   s2bit = 0b00000100,  // 1.5 for 5bit data; 2 otherwise
-  // divisor latch access bit
-  dlab = 0b10000000,
+  dlab = 0b10000000,   // divisor latch access bit
 };
 
 /* Line Status Register */
@@ -35,6 +31,10 @@ enum LineStatusRegister : uint8_t {
   ERRO = 0b10000000,  // impending error: see if there is an error with a word in the input buffer
 };
 
+// TODO InterruptControlRegister
+// TODO FifoControlRegister
+// TODO ModemControlRegister
+
 SerialPort::SerialPort() {
   /*
    * The serial controller (UART) has a baud rate of 115200 ticks per second; to limit the speed of the port set the
@@ -54,6 +54,16 @@ SerialPort::SerialPort() {
 
   port.write(0xc7, FifoControl);      // enable FIFO, clear, with 14-byte threshold
   port.write(0x0b, ModemControl);     // IRQ enabled, RTS/DSR set
+
+  // test serial port
+  port.write(0x1e, ModemControl);  // set in loopback mode
+  port.write(0xae);                // write 0xae to port
+  self_check_okay = (port.read() == 0xae);
+
+  // if not faulty, set in normal operation mode
+  if (self_check_okay) {
+    port.write(0x0f, ModemControl);
+  }
 }
 
 bool SerialPort::ready_read() {
@@ -61,9 +71,7 @@ bool SerialPort::ready_read() {
 }
 
 uint8_t SerialPort::read() {
-  while (!ready_read()) {
-    asm volatile("nop");
-  }
+  while (!ready_read()) asm volatile("nop");
   return port.read();
 }
 
@@ -72,9 +80,7 @@ bool SerialPort::ready_write() {
 }
 
 void SerialPort::write(char c) {
-  while (!ready_write()) {
-    asm volatile("nop");
-  }
+  while (!ready_write()) asm volatile("nop");
 
   switch (c) {
     case '\n':
diff --git a/drivers/serial.h b/drivers/serial.h
index 0579dd4..896d831 100644
--- a/drivers/serial.h
+++ b/drivers/serial.h
@@ -16,20 +16,22 @@ public:
   SerialPort();
   ~SerialPort() = default;
 
+  bool self_check() const { return self_check_okay; }
+
   bool ready_read();
   uint8_t read();
 
   bool ready_write();
   void write(char c) override;
   void write(ViewIterator& iter) override {
-    while (iter) {
-      write(iter.next());
-    }
+    while (iter) write(iter.next());
   }
 
   void update_cursor() override {}
 
 private:
+  bool self_check_okay;
+
   enum PortOffset : uint16_t {
     BaudDiv_l = 0,         // if dlab is set
     BaudDiv_h = 1,         // if dlab is set
diff --git a/src/kernel.cc b/src/kernel.cc
index 624f472..1139e3b 100644
--- a/src/kernel.cc
+++ b/src/kernel.cc
@@ -20,7 +20,7 @@ void dump_gdt();
 
 void kernel_main([[maybe_unused]] uint32_t mb_magic, [[maybe_unused]] uint32_t mb_addr) {
   SerialPort s0;
-  Console::set(&s0);
+  if (s0.self_check()) Console::set(&s0);
 
   CGA terminal;
   Console::set(&terminal);