z7 uart0 buffered read

bsp_z7/newlib/read.c

@@ -1,5 +1,34 @@
+#include "xil_printf.h"
+#include "xparameters.h"
 
+#include "../hardware/interface_access.h"
+#include "../hardware/interface_fds.h"
 
-int _read(int file, char *ptr, int len) {
-  return 0;
+// newlib offers a (weak) write implementation which
+// is reentrant by calling _read_r which in turn
+// relies on _read which we implement here.
+// This way, we get a global, reentrant read implementation
+// NOTE: This might be architecture dependent, so check your
+// newlib implementation!
+int _read(int fd, char *ptr, int len) {
+  if (ptr == NULL) {
+    return 0;
+  }
+  
+  // 0 is stdin, TODO: do we support it?
+  if (fd < 1) {
+    return -1;
+  }
+  
+  // stdout and stderr
+  if (fd < 3) {
+    return -1;
+  }
+
+  if (fd < INTERFACE_FDS_NEXT) {
+    return hw_interface_read(fd, ptr, len);
+  }
+
+  // we do not have dynamic fds, so fd is invalid
+  return -1;
 }