SPI Engine Offload Control Interface

The SPI-Engine offload control interface is used to configure and control a SPI Engine Offload Module. It is used to activate/deactivate the core as well re-program the command and SDO data RAM.

Files

Name	Description
library/spi_engine/interfaces/spi_engine_offload_ctrl_rtl.xml	Interface definition file

Signal Pins

Name	Direction (Manager)	Description
cmd_wr_en	Output	If asserted cmd_wr_data is written to the command memory.
cmd_wr_data	Output	Data to write to the command memory.
sdo_wr_en	Output	If asserted sdo_wr_data is written to the SDO data memory.
sdo_wr_data	Output	Data to write to the SDO data memory.
mem_reset	Output	Reset the contents of both the command and SDO data memory.
enable	Output	If asserted the connected offload core will get enabled.
enabled	Input	If asserted the connected offload core is enabled.

Theory of Operation

The SPI-Engine offload core typically implements to RAMs, one for the command stream and one for the SDO data stream. If the mem_reset signal is asserted the content of both memories is cleared. Asserting cmd_wr_en will write the value of cmd_wr_data to the command memory and increase the write address by one. The next time cmd_wr_en is asserted the next entry in the memory will be written and so on. If cmd_wr_en is asserted more times than the size of the command memory (without a reset in between) undefined behavior will occur. sdo_wr_en and sdo_wr_data behave analogously for the SDO data memory.

If the enable signal the is asserted the SPI-Engine offload core will be active, this means it will listen to external trigger events and execute the stored SPI transfer when the external trigger is asserted. If enable is not asserted the core will no longer listen to trigger events and will not start new transfers. But it might still be busy executing a SPI transfer that was started previously. The enabled signal is used to indicate this and it will stay asserted even after enable as been deasserted until the currently active SPI transfer has been completed.

If either enable or enabled is asserted cmd_wr_en, sdo_wr_en, or memt_reset must not be asserted, otherwise undefined behavior can occur. In other words as long as the SPI-Engine offload core is active the content of both the command and SDO data memory must remain stable and be consistent.