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====== SPI-Engine Offload Control Interface ======

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

===== Files =====

^ Name ^ Description ^
| [[github>hdl?master/library/spi_engine/interfaces/spi_engine_offload_ctrl.xml|spi_engine_offload_ctrl.xml]] | Interface definition file |

===== Signal Pins =====

^ Name ^ Direction (Master) ^ 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 then 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.

===== More Information =====
  * [[.|SPI Engine Framework]]
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