diagdummy Add srpr2 subcommand for contiguous printing to serial (and testing access races)

user/diagdummy/serial.c

@@ -7,7 +7,7 @@
 #define RECVB     2
 #define RECVREADY 3
 
-void diagdummy_serialprint(void) {
+void diagdummy_srpr(void) {
   char *str = "Hello world\n";
 
   if (argslen() >= 2) {
@@ -24,3 +24,20 @@ void diagdummy_serialprint(void) {
     s++;
   }
 }
+
+void diagdummy_srpr2(void) {
+  if (argslen() < 2) {
+    return;
+  }
+    
+  char *str = args()[1];
+
+  Dev_t serialdev;
+  dev_gethandle(&serialdev, "serialdev");
+
+  for (;;) {
+    while (!dev_cmd(&serialdev, SENDREADY, NULL, 0));
+    dev_cmd(&serialdev, SENDB, str, 1);
+    schedsleep(500);
+  }
+}