41-553M.pdf - Pickering Interfaces

ERROR INJECTION
intermittent, random errors in bus controller transmissions without stopping
the BC schedule.
The following examples demonstrate how to define errors, tag messages and
enable error injection. Note that the examples in this chapter are similar to
those in earlier chapters, except that they ignore data to focus on the process
of error injection.
6.2 Errors in BC Transmissions: Unscheduled Messages
The following code modifies Example 1 in Section 4.1 so that the message
transmitted has a parity error in its command word.
XMITFIELDS Msg;
Card = L13_CardOpen(CARDNUM);
L13_CardReset(Card);
L13_BCConfig(BCCFG_DEFAULT, Card);
Msg.ctrlflags = MSGCRT_BCRT;
Msg.cwd1 = 0x0843;
Msg.data[0] = some_value0;
Msg.data[1] = some_value1;
Msg.data[2] = some_value2;
L13_ErrorDefine(ERRDEF_PAR, 0, 0, ERRDEF_CWD1, 0, Card);
L13_ErrorCtrl(ERRCTRL_ONCE | ERRCTRL_ANYMSG, Card);
L13_BCTransmitMsg(&Msg, Card);
if(Msg.errflags & (MSGERR_NORESP | MSGERR_ANYERR))
{
// The RT did not respond or had an error in its response.
}
else
{
// The message was completed successfully.
// Check Msg.status1 for the RT’s status word response.
}
L13_CardClose(Card);
Fig. 6-1 Example 6: Errors in unscheduled BC transmissions
Only the L13_ErrorDefine and L13_ErrorCtrl functions are added
to Example 1 (Fig. 4-1). L13_ErrorDefine specifies that the first command
word in a message should contain a parity error. L13_ErrorCtrl
arms the 41-553 error-injection mechanism. This example can safely use the
ERRCTRL_ANYMSG flag since only one message is to be transmitted.
When L13_BCTransmitMsg is executed, the transmitted message contains
incorrect parity in its command word as specified by the parameters of
L13_ErrorDefine. According to MIL-STD-1553, an RT should never
respond to invalid commands. Thus, in this example, no response is expected
from the RT, and the first block of the if-else statement should be executed.
41-553 User’s Manual 6-3