1 files changed, 78 insertions, 0 deletions
diff --git a/machine/htif.c b/machine/htif.c
new file mode 100644
index 0000000..a513305
--- /dev/null
+++ b/machine/htif.c
@@ -0,0 +1,78 @@
+#include "htif.h"
+#include "atomic.h"
+#include "mtrap.h"
+
+volatile uint64_t tohost __attribute__((aligned(64))) __attribute__((section("htif")));
+volatile uint64_t fromhost __attribute__((aligned(64))) __attribute__((section("htif")));
+volatile int htif_console_buf;
+static spinlock_t htif_lock = SPINLOCK_INIT;
+
+static void request_htif_keyboard_interrupt()
+{
+  assert(tohost == 0);
+  tohost = TOHOST_CMD(1, 0, 0);
+}
+
+static void __check_fromhost()
+{
+  // we should only be interrupted by keypresses
+  uint64_t fh = fromhost;
+  if (!fh)
+    return;
+  if (!(FROMHOST_DEV(fh) == 1 && FROMHOST_CMD(fh) == 0))
+    die("unexpected htif interrupt");
+  htif_console_buf = 1 + (uint8_t)FROMHOST_DATA(fh);
+  fromhost = 0;
+}
+
+int htif_console_getchar()
+{
+  if (spinlock_trylock(&htif_lock) == 0) {
+    __check_fromhost();
+    spinlock_unlock(&htif_lock);
+  }
+
+  int ch = atomic_swap(&htif_console_buf, -1);
+  if (ch >= 0)
+    request_htif_keyboard_interrupt();
+  return ch - 1;
+}
+
+static void do_tohost_fromhost(uintptr_t dev, uintptr_t cmd, uintptr_t data)
+{
+  spinlock_lock(&htif_lock);
+    while (tohost)
+      __check_fromhost();
+    tohost = TOHOST_CMD(dev, cmd, data);
+
+    while (1) {
+      uint64_t fh = fromhost;
+      if (fh) {
+        if (FROMHOST_DEV(fh) == dev && FROMHOST_CMD(fh) == cmd) {
+          fromhost = 0;
+          break;
+        }
+        __check_fromhost();
+      }
+    }
+  spinlock_unlock(&htif_lock);
+}
+
+uintptr_t htif_syscall(uintptr_t arg)
+{
+  do_tohost_fromhost(0, 0, arg);
+  return 0;
+}
+
+void htif_console_putchar(uint8_t ch)
+{
+  do_tohost_fromhost(1, 1, ch);
+}
+
+void htif_poweroff()
+{
+  while (1) {
+    fromhost = 0;
+    tohost = 1;
+  }
+}