adds board specific read for iss, changes read implementation

env/iss/bsp_read.c

@@ -0,0 +1,19 @@
+#include <stdint.h>
+#include <stdio.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+ssize_t _bsp_read(int fd, void *ptr, size_t len) {
+  uint8_t *current = (uint8_t *)ptr;
+  volatile uint32_t *uart_rx = (uint32_t *)0xFFFF0000;
+  ssize_t result = 0;
+  if (isatty(fd)) {
+    for (current = (uint8_t *)ptr; (current < ((uint8_t *)ptr) + len);
+         current++) {
+      *current = *uart_rx;
+      result++;
+    }
+    return result;
+  }
+  return EOF;
+}