LISA-U2 series - System integration manual
UBX-13001118 - R27
System description
Page 82 of 183
C1-Public
Host-initiated transfer with a sleeping local device
Figure 43: Data transfer initiated by the application processor (host) with a sleeping LISA-U2 module (local device)
When the local device is sleeping (idle mode), the following actions happen:
1.
The host wakes the local deviceby setting the
SPI_MRDY
line active.
2.
As soon as the local device is awake, it signals it by activating
SPI_SRDY
.
3.
The host activates the clock and the two processors exchange the communication header and
data.
4.
If the data has been exchanged, the local device deactivates
SPI_SRDY
to process the received
information. The host does not need to de-assert
SPI_MRDY
as it controls the
SPI_SCLK
.
5.
After the preparation, the local device activates
SPI_SRDY
again and waits for
SPI_SCLK
activation. When the clock is active, all data is transferred without intervention. If there is more
data to transfer (flag set in any of the headers), the process will repeat from step 3.
Local device ended transfer
Figure 44: Data transfer terminated and then restarted by LISA-U2 module (local device )
Starting from the state where data transfer is ongoing, the following actions will happen:
1.
In case of the last transfer, the host will lower its
SPI_MRDY
line. After the data transfer is
finished, the line must be low. If the local device has already set its
SPI_SRDY
line, the host must
raise its line to initiate the next transfer (local device-waking-procedure).
2.
If the data has been exchanged, the local device will deactivate
SPI_SRDY
to process the received
information. This is the normal behavior.
3.
The local device will indicate the host that is ready to send data by activating
SPI_SRDY.
4.
When the host is ready to send, it will signalize this by activating
SPI_MRDY
. This is optional,
when
SPI_MRDY
is low before.
5.
The local device indicates immediately after a transfer termination that it is ready to start
transmission again. In this case, the local device will raise
SPI_SRDY
again. The
SPI_MRDY
line
can be either high or low: the host only needs to ensure that the
SPI_SRDY
change will be
detected correctly via interrupt.
☞
For more details regarding IPC communication protocol, see the SPI application note
SPI_MRDY
SPI_SRDY
DATA EXCHG
1
2
4
5
Header
Data
Header
3
SPI_MRDY
SPI_SRDY
DATA EXCHG
5
2
1
Header
Data
3
4
