separate source into kernel/ user/ mkfs/

1 files changed, 75 insertions, 0 deletions

diff --git a/kernel/uart.c b/kernel/uart.c
new file mode 100644
index 0000000..35fac1b
--- /dev/null
+++ b/kernel/uart.c
@@ -0,0 +1,75 @@
+#include "types.h"
+#include "param.h"
+#include "memlayout.h"
+#include "riscv.h"
+#include "proc.h"
+#include "spinlock.h"
+#include "defs.h"
+
+//
+// qemu -machine virt has a 16550a UART
+// qemu/hw/riscv/virt.c
+// http://byterunner.com/16550.html
+//
+// caller should lock.
+//
+
+// address of one of the registers
+#define R(reg) ((volatile unsigned char *)(UART0 + reg))
+
+void
+uartinit(void)
+{
+  // disable interrupts -- IER
+  *R(1) = 0x00;
+
+  // special mode to set baud rate
+  *R(3) = 0x80;
+
+  // LSB for baud rate of 38.4K
+  *R(0) = 0x03;
+
+  // MSB for baud rate of 38.4K
+  *R(1) = 0x00;
+
+  // leave set-baud mode,
+  // and set word length to 8 bits, no parity.
+  *R(3) = 0x03;
+
+  // reset and enable FIFOs -- FCR.
+  *R(2) = 0x07;
+
+  // enable receive interrupts -- IER.
+  *R(1) = 0x01;
+}
+
+void
+uartputc(int c)
+{
+  // wait for Transmit Holding Empty to be set in LSR.
+  while((*R(5) & (1 << 5)) == 0)
+    ;
+  *R(0) = c;
+}
+
+int
+uartgetc(void)
+{
+  if(*R(5) & 0x01){
+    // input data is ready.
+    return *R(0);
+  } else {
+    return -1;
+  }
+}
+
+void
+uartintr(void)
+{
+  while(1){
+    int c = uartgetc();
+    if(c == -1)
+      break;
+    consoleintr(c);
+  }
+}