portable device access api based on unix file descriptors

bsp_z7/newlib/write.c

@@ -1,15 +1,41 @@
 #include "xil_printf.h"
 #include "xparameters.h"
 
-int write(int file, char *ptr, int len) {
+#include "../hardware/interface_access.h"
+#include "../hardware/interface_fds.h"
+
+
+// newlib offers a (weak) write implementation which
+// is reentrant by calling _write_r which in turn
+// relies on _write which we implement here.
+// This way, we get a global, reentrant write implementation
+// NOTE: This might be architecture dependent, so check your
+// newlib implementation!
+int _write(int fd, const char *ptr, int len) {
   if (ptr == NULL) {
     return 0;
   }
-  // TODO file descriptors
-  int todo;
-
-  for (todo = 0; todo < len; todo++) {
-    outbyte(*ptr++);
+  
+  // 0 is stdin, do not write to it
+  if (fd < 1) {
+    return -1; // TODO error
   }
-  return len;
+  // we only support a single debug UART, so
+  // stdout and stderr are the same and go to the xiling stdout UART
+  // TODO switch to a hw_interface_write() instead?
+  if (fd < 3) {
+    int todo;
+
+    for (todo = 0; todo < len; todo++) {
+      outbyte(*ptr++);
+    }
+    return len;
+  }
+
+  if (fd < INTERFACE_FDS_NEXT) {
+    return hw_interface_write(fd, ptr, len);
+  }
+
+  // we do not have dynamic fds, so fd is invalid
+  return -1;
 }