[battery] Tie into the periodic function to update APM info

Tie into the periodic function so we can get the APM info.

For now it's not checking that some time has elapsed, the hope
is that it'll just be driven by md_main_loop() / 5 second select
timeout.

battery_module.c

@@ -11,6 +11,9 @@
 
 #include "libami.h"
 
+/* XXX should be an md method */
+extern void (*md_periodic_func)(void);
+
 /*
  * Test battery module for FreeBSD, using APM.
  */
@@ -45,21 +48,29 @@ get_apm_info(void)
 	return true;
 }
 
+static void
+periodic_func(void)
+{
+	fprintf(stderr, "Ha!\n");
+	get_apm_info();
+}
+
 int main(int argc, char *argv[])
 {
-  char *arg=md_init(argc, argv);
+  char *arg;
+
+  arg = md_init(argc, argv);
 
   progname=argv[0];
 
+  md_periodic_func = periodic_func;
+
   apm_fd = open(APM_DEV, O_RDONLY);
   if (apm_fd < 0) {
     err(127, "open");
   }
 
-  /*
-   * XXX TODO: how do I actually get this to run once
-   * a second in the main loop?
-   */
+  /* initial battery info */
   get_apm_info();
 
   md_main_loop();