The command to get serial transmission delay is txdelay.
"get txdelay"
The return value is in bit unit.
<?php
include "/lib/sd_spc.php";
$sid = 14;
spc_reset();
spc_sync_baud(115200);
spc_request_dev($sid, "set uart 115200N81");
spc_request_dev($sid, "set txdelay 10");
echo spc_request_dev($sid, "get txdelay"), "\r\n"; // output: 10
spc_request_dev($sid, "set txdelay 0");
echo spc_request_dev($sid, "get txdelay"); // output: 0
?>