读取指定UM(易失性内存)的数据
int um_read(int $um_id, int $offset, string &$rbuf, int $rlen)
读取数据大小(字节)
<?php
include "/lib/sd_340.php";
$rbuf = "";
um_read(0, 0, $rbuf, 10); // Reading 10 bytes from address 0 of the UM0
hexdump($rbuf); // Outputting the data
?>