uz_dac_spi_interface

The uz_dac_interface IP-Core takes input values for the uz_dac8831 DAC adapter card from the processor by AXI and writes them to the adapter card. The IP-Core is designed for simplicity. One AXI register for each DAC and a trigger conversion register is present. On a rising edge on the trigger conversion register (only possible by AXI), all values are written to all DACs. The SPI clk frequency can not be changed during runtime and is hard-coded to \(f_{SPI}=0.5 \cdot f_{IP-Core}\). The software driver features a conversion factor for each of the DAC channels to account for different gains in the OpAMP circuit of the card.

Software interface

Example

The following example initializes one driver instance and writes values to it. Note that the values of DAC1 and DAC8 are out of range for the +- 5V output and will clip accordingly. However, supplying out of range values does not trigger an assertion to be able to model the behavior of clipping sensors if they measure out-of-range values.

Listing 196 Initialization of the driver instance. Base address depends on xparameters.h, gains are set to their nominal value in this case (2.0f).

#include "uz_dac_interface.h"
#include "xparameters.h"
#include "uz_array.h"

struct uz_dac_interface_config_t dac_config={
    .base_address=XPAR_UZ_USER_UZ_DAC_SPI_INTERFACE_0_BASEADDR, // Depends on xparameters.h!
    .ip_clk_frequency_Hz=100000000,
    .gain={2.0f,2.0f,2.0f,2.0f,2.0f,2.0f,2.0f,2.0f}
};
uz_dac_interface_t* dac_instance=uz_dac_interface_init(dac_config);

Listing 197 Writes values of dac_input to the DAC channels

float dac_input[8]={-6.0f, -5.0f, -4.0f, -3.0f, 1.0f, 3.0f, 4.0f, 8.0f};
    uz_array_float_t dac_input_array={
    .data=&dac_input[0],
    .length=UZ_ARRAY_SIZE(dac_input)
};
uz_dac_interface_set_ouput_values(dac_instance,&dac_input_array);

Warning

The DAC always outputs the last value present in the DAC latch register. The user has to take care of safe DAC output states for the application before stopping control algorithms in the ISR or before flashing the MPSoC during testing.

Driver reference

UZ_DAC_INTERFACE_OUTPUT_CHANNELS

Defines the maximum number of DAC channels on the PCB. Has to be 8!

typedef struct uz_dac_interface_t uz_dac_interface_t

Typedef for uz_dac_interface object definition.

struct uz_dac_interface_config_t

Configuration struct for the DAC Interface IP-Core.

Public Members

uint32_t base_address

Base address of the IP-Core instance to which the driver is coupled

uint32_t ip_clk_frequency_Hz

Clock frequency of IP-Core

float gain[UZ_DAC_INTERFACE_OUTPUT_CHANNELS]

Gain of the output OpAMPs of the DAC card. Usually set to 2.0f, but can be fine-tuned to match actual hardware.

uz_dac_interface_t *uz_dac_interface_init(struct uz_dac_interface_config_t config)

Initializes an instance of the DAC driver.

Parameters:

• config – Config struct for the DAC

Returns:

uz_dac_interface_t* Pointer to an instance of the driver

void uz_dac_interface_set_ouput_values(uz_dac_interface_t *self, uz_array_float_t *output_values)

Writes the set-point to all DAC simultaneously. Saturates internally to allow for clipped operation.

Parameters:

• self – Pointer to driver instance

• output_values – Array of set-point values

IP-Core interface (Vivado)

The FPGA interface of the IP-Core is a single signal while the uz_dac8831 PCB expects LVDS signals. Therefore, additional Utility Buffers (with C Buf Type set to OBUFDS) have to be added to the Vivado block design between the output ports and the uz_dac_spi_interface IP-Core. Constraints for using the DAC card uz_dac8831 in the slot A3 are supplied in the constraints folder (uz_dac8831_A3.xdc). The SPI clk frequency of the IP-Core output is always half of the IP_CORE_CLK. The IP-Core is only tested with IPCORE_CLK and AXI_ACLK connected to 100 MHz clock!

Fig. 345 Wiring to output ports.

Fig. 346 Detailed setup of uz_dac_spi_interface IP-Core and Utility Buffer

Fig. 347 Settings of Utility Buffer

Table 113 Interface and ports of the IP-Core

Port Name	Port type	Data type	Target Platform Interfaces	Mapping	Function
trigger_write	Inport	boolean	AXI4	x”100”	Current values from data_out_1..8 are written output to SPI interface
dac_data_1	Inport	int16	AXI4	x”104”	Data that should be sent to DAC1
dac_data_2	Inport	int16	AXI4	x”108”	Data that should be sent to DAC2
dac_data_3	Inport	int16	AXI4	x”10C”	Data that should be sent to DAC3
dac_data_4	Inport	int16	AXI4	x”110”	Data that should be sent to DAC4
dac_data_5	Inport	int16	AXI4	x”114”	Data that should be sent to DAC5
dac_data_6	Inport	int16	AXI4	x”118”	Data that should be sent to DAC6
dac_data_7	Inport	int16	AXI4	x”11C”	Data that should be sent to DAC7
dac_data_8	Inport	int16	AXI4	x”120”	Data that should be sent to DAC8
spi_clk_out	Outport	boolean	External Port		CLK for SPI interface of all DAC - to be connected to Utitlity buffer (OBUFDS)
cs_out	Outport	boolean	External Port		CS for SPI interface of all DAC
data_out_1	Outport	boolean	External Port		Connection to DAC1 - to be connected to Utitlity buffer (OBUFDS)
data_out_2	Outport	boolean	External Port		Connection to DAC2 - to be connected to Utitlity buffer (OBUFDS)
data_out_3	Outport	boolean	External Port		Connection to DAC3 - to be connected to Utitlity buffer (OBUFDS)
data_out_4	Outport	boolean	External Port		Connection to DAC4 - to be connected to Utitlity buffer (OBUFDS)
data_out_5	Outport	boolean	External Port		Connection to DAC5 - to be connected to Utitlity buffer (OBUFDS)
data_out_6	Outport	boolean	External Port		Connection to DAC6 - to be connected to Utitlity buffer (OBUFDS)
data_out_7	Outport	boolean	External Port		Connection to DAC7 - to be connected to Utitlity buffer (OBUFDS)
data_out_8	Outport	boolean	External Port		Connection to DAC8 - to be connected to Utitlity buffer (OBUFDS)

References

• Data sheet of DAC8831: https://www.ti.com/lit/ds/slas449d/slas449d.pdf?ts=1653291212982