AUTOSAR COM · Sheet
COM at a glance
Every feature of COM on one page, in plain words. The number is the lesson that explains it.
Applicationsingle values: signals
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COMpacks and unpacks, decides when
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Below COMpackets (I-PDUs) to and from the bus
Sending
| Word | Set on | Means | |
|---|---|---|---|
TRIGGERED | Signal | Writing it makes the packet go out now. Flavours: only on change, with or without repeats. | 2, 3 |
PENDING | Signal | Writing it sends nothing. The value rides along on the next send. | 2 |
DIRECT | Packet | No timer. Sent only when a triggered signal is written. | 2 |
PERIODIC | Packet | Timer only. | 2 |
MIXED | Packet | Timer, plus right away on a triggered write. | 2 |
NONE | Packet | COM never starts a send itself. | 2 |
| Repeats | Packet | Send the packet several times after one write. | 3 |
| Minimum gap | Packet | Pause after a send before the same packet may go again. Sends inside the pause wait. | 3 |
| Two send settings | Packet | A "true" and a "false" setting. Conditions on signal values pick one. | 4 |
| Send timeout | Signal | Alarm, once, if the bus does not confirm a send in time. | 6 |
Receiving
| Word | Set on | Means | |
|---|---|---|---|
IMMEDIATE | Packet | Application is told the moment the packet arrives. | 2 |
DEFERRED | Packet | Application is told at COM's next heartbeat. | 2 |
| Start value | Signal | The value handed out until a real one arrives. | 5 |
| Update-bit | Signal | One bit saying "this signal is new". Not set: receiver ignores the signal. | 5 |
| Receive timeout | Signal | Alarm, repeating, when nothing arrives in time. Then keep, reset or substitute the value. | 6 |
| Invalid value | Signal | A reserved value meaning "no good value". Receiver notifies or replaces. | 7 |
| Filter | Signal | A pass-or-block rule for received values. Eight rules. | 8 |
| Messages | Signal | New value, overdue, invalid, sent, not sent in time, could not be sent. | 9 |
Order of the receiving steps
- Reset the packet's timeout stopwatch
- Check the update-bit
- Convert byte order and sign
- Check for the invalid value
- Filter
- Reset the signal's own timeout stopwatch
- Tell the application
Organising
| Feature | Means | |
|---|---|---|
| Signal group | Values that belong together are collected in a staging area and handed over as one set. | 10 |
| Packet group | A named set of packets that is started and stopped as a whole, from outside COM. All stopped after switch-on. | 11 |
| Signal gateway | Fixed rules that copy a received signal into outgoing packets, at the gateway's heartbeat. | 12 |
| Big packet | Too big for one frame: sent in pieces by a helper below COM. | 13 |
| Changing size | A row of bytes with varying length, last in its packet. | 13 |
| Fast lane | COM passes a finished block of bytes through untouched. | 13 |
COM's borders
| Call | Meaning |
|---|---|
Com_SendSignal / Com_ReceiveSignal | Write / read one signal, from above. |
PduR_ComTransmit | COM hands a packet down. |
Com_TxConfirmation | "Your packet is on the bus." |
Com_RxIndication | "A packet arrived for you." |
Com_TriggerTransmit | "Give me the packet's content now." |
See lesson 14 for the road below COM, lesson 15 for the settings, and the signal packing sheet for bits. Checked against the AUTOSAR COM specification, R25-11.