The SPI bus interface carries logical low-level SPI bus signals.
|Interface definition file
|SPI SDO (MOSI) signal.
sdo tri-state enable. If 1 the MOSI signal should be tristated and not be connected to
| SPI SDI (MISO) signal. Execution module supports max 8 individual
|SPI chip-select signal.
| If set to 1 the bus should operate in three-wire mode. In three-wire mode
sdi is connected to MOSI instead of MISO.
The SPI bus interface only carries a logical representation of the low-level SPI bus signals. The top-level module in the FPGA design project is responsible for translating the signal to physical SPI bus signals by instantiating and connecting it to appropriate IO primitives.
cs signals can typically be directly connected to a output buffer.
sdi should be connected to a mux, that depending on the setting of the
three_wire signal connects to a input buffer connected to the
miso signal or to a input buffer connected to the
mosi signal. The
sdo signal should be connected to a output tri-state buffer with the
sdo_t signal controlling the tri-state setting.
In some configurations three-wire support may not be required and
sdi can directly be connected to the input buffer for the
miso signal. Similarly when
mosi tri-stating is not required the
sdo signal can be directly connected to the
mosi signal leaving the
sdo_t signal unconnected.
The following example Verilog code shows the most generic IO configuration, which represents the diagram above. Depending on system requirements some simplification might be possible.
Signals with phy prefix are assumed to be connected to the physical input/output pins and signals with the spi prefix are assumed to be connected SPI-Engine bus interface.
assign phy_sclk = spi_sclk; assign phy_cs = spi_cs; assign phy_mosi = spi_sdo_t ? 1'bz : spi_sdo; assign spi_sdi = spi_three_wire ? phy_mosi : phy_miso;