1 files changed, 76 insertions, 0 deletions
diff --git a/machine/uart.c b/machine/uart.c
new file mode 100644
index 0000000..0645500
--- /dev/null
+++ b/machine/uart.c
@@ -0,0 +1,76 @@
+#include <string.h>
+#include "uart.h"
+#include "fdt.h"
+
+volatile uint32_t* uart;
+
+void uart_putchar(uint8_t ch)
+{
+#ifdef __riscv_atomic
+    int32_t r;
+    do {
+      __asm__ __volatile__ (
+        "amoor.w %0, %2, %1\n"
+        : "=r" (r), "+A" (uart[UART_REG_TXFIFO])
+        : "r" (ch));
+    } while (r < 0);
+#else
+    volatile uint32_t *tx = uart + UART_REG_TXFIFO;
+    while ((int32_t)(*tx) < 0);
+    *tx = ch;
+#endif
+}
+
+int uart_getchar()
+{
+  int32_t ch = uart[UART_REG_RXFIFO];
+  if (ch < 0) return -1;
+  return ch;
+}
+
+struct uart_scan
+{
+  int compat;
+  uint64_t reg;
+};
+
+static void uart_open(const struct fdt_scan_node *node, void *extra)
+{
+  struct uart_scan *scan = (struct uart_scan *)extra;
+  memset(scan, 0, sizeof(*scan));
+}
+
+static void uart_prop(const struct fdt_scan_prop *prop, void *extra)
+{
+  struct uart_scan *scan = (struct uart_scan *)extra;
+  if (!strcmp(prop->name, "compatible") && !strcmp((const char*)prop->value, "sifive,uart0")) {
+    scan->compat = 1;
+  } else if (!strcmp(prop->name, "reg")) {
+    fdt_get_address(prop->node->parent, prop->value, &scan->reg);
+  }
+}
+
+static void uart_done(const struct fdt_scan_node *node, void *extra)
+{
+  struct uart_scan *scan = (struct uart_scan *)extra;
+  if (!scan->compat || !scan->reg || uart) return;
+
+  // Enable Rx/Tx channels
+  uart = (void*)(uintptr_t)scan->reg;
+  uart[UART_REG_TXCTRL] = UART_TXEN;
+  uart[UART_REG_RXCTRL] = UART_RXEN;
+}
+
+void query_uart(uintptr_t fdt)
+{
+  struct fdt_cb cb;
+  struct uart_scan scan;
+
+  memset(&cb, 0, sizeof(cb));
+  cb.open = uart_open;
+  cb.prop = uart_prop;
+  cb.done = uart_done;
+  cb.extra = &scan;
+
+  fdt_scan(fdt, &cb);
+}