User's Manual

LISA-U1/LISA-H1 series - System Integration Manual

3G.G2-HW-10002-2 Advance Information System description

Page 58 of 116

SPI_MRDY

SPI_SRDY

DATA_EXCHANGE

SPI_MOSI

SPI_MISO

Header Data

SPI_SCLK

Figure 31: IPC Data Flow: SPI_MRDY and SPI_SRDY line usage combined with the SPI protocol

For the correct implementation of the SPI protocol, the frame size is known by both sides before a packet

transfer of each packet. The frame is composed by a header with fixed size (always 4 bytes) and a payload with

variable length (must be a multiple of 4 bytes).

The same amount of data is exchanged in both directions simultaneously. Both sides set their readiness lines

(SPI_MRDY / SPI_SRDY) independently when they are ready to transfer data. For the correct transmission of the

data the other side must wait for the activating interrupt to allow the transfer of the other side.

The master starts the clock shortly after SPI_MRDY and SPI_SRDY are set to active. The amount of clocks is

exactly that one of the frame-size to be transferred. The SPI_SRDY line will be set down after the end of the

clock. The SPI_MRDY line is also set inactive with the end of the clock, but in case of a big transfer containing

multiple packets, the SPI_MRDY line stays active.

1.9.4.2 IPC communication examples

In the following, three IPC communication scenarios are described:

 Slave initiated data transfer, with a sleeping master

 Master initiated data transfer, with a sleeping slave

 Slave ended data transfer

Slave initiated transfer with a sleeping master

Figure 32: Data transfer initiated by LISA-U1/LISA-H1 series module (slave), with a sleeping application processor (master)

When the master is sleeping (idle mode), the following actions happen:

1. The slave indicates the master that is ready to send data by activating SPI_SRDY

2. When the master becomes ready to send, it signalizes this by activating SPI_MRDY

3. The master activates the clock and the two processors exchange the communication header and data

SPI_MRDY

SPI_SRDY

DATA EXCHG

Header

Data

Header