AD3552R High Speed

AD3552R Dual Channel, 16-Bit, 33 MUPS, Multispan, Multi-IO SPI DAC Linux device driver.

The AD3552R is a low drift, dual channel, ultra-fast, 16-bit accuracy, current output digital-to-analog converter (DAC) that can be configured in multiple voltage span ranges. The AD3552R operates with a fixed 2.5 V reference. Each DAC incorporates three drift-compensating feedback resistors for the required external trans-impedance amplifier (TIA) that scales the output voltage. Offset and gain scaling registers allow for the generation of multiple output span ranges, such as 0 V to 2.5 V, 0 V to 5 V, 0 V to 10 V, −5 V to +5 V, and −10 V to +10 V, and custom intermediate ranges with full 16-bit resolution. The DAC can operate in fast mode for maximum speed or precision mode for maximum accuracy.

Supported Devices

Evaluation Boards

Description

This is a Linux industrial I/O (Linux Industrial I/O Subsystem) subsystem driver for the high-speed variant of the AD35xxR DACs. The DAC is driven through the AXI AD3552R FPGA IP core, which implements the (dual or quad) SPI data lanes, DDR streaming and DMA transfers needed to reach the maximum sample rate.

The driver is split in two parts using the IIO backend framework:

adi-axi-dac: the AXI AD3552R IP core driver (backend). It also acts as the SPI-like bus controller for the DAC.
ad3552r-hs: the DAC driver (frontend), probed from a child node of the IP core node.

This driver replaces the former out-of-tree axi-ad3552r driver (compatible adi,axi-ad3552r handled by a single driver). The device tree layout and the sysfs interface differ from that driver.

Source Code

Status

Source	Mainlined?
drivers/iio/dac/ad3552r-hs.c	Yes
drivers/iio/dac/adi-axi-dac.c	Yes

Files

Function	File
DAC driver (frontend)	drivers/iio/dac/ad3552r-hs.c
common code	drivers/iio/dac/ad3552r-common.c
include	drivers/iio/dac/ad3552r.h
AXI DAC IP core driver (backend)	drivers/iio/dac/adi-axi-dac.c
kernel documentation	Documentation/iio/ad3552r.rst

Adding Linux driver support

Kernel configuration

Configure kernel with make menuconfig (alternatively use make xconfig or make qconfig)

Linux Kernel Configuration
    Device Drivers  --->
        <*>     Industrial I/O support --->
                  Digital to analog converters  --->
                      [--snip--]
                      <*>   Analog Devices AD3552R DAC High Speed driver
                      [--snip--]
                      <*>   Analog Devices Generic AXI DAC IP core driver
                      [--snip--]

Devicetree configuration

The AXI AD3552R IP core node (backend):

compatible: adi,axi-ad3552r
reg: IP core register region.
dmas, dma-names: Transmit DMA channel, "tx".
clocks, clock-names: s_axi_aclk (AXI bus clock) and dac_clk (DAC interface clock).
#io-backend-cells: <0>.

The DAC child node (frontend):

compatible: adi,ad3541r, adi,ad3542r, adi,ad3551r or adi,ad3552r.
reg: <0>.
spi-max-frequency: Maximum frequency for register access.
io-backends: Phandle to the AXI AD3552R IP core node.
channel@N sub-nodes with adi,output-range-microvolt (or custom-output-range-config).

Optional properties include reset-gpios, ldac-gpios, vref-supply and adi,vref-out-en. See Documentation/devicetree/bindings/iio/dac/adi,axi-dac.yaml and Documentation/devicetree/bindings/iio/dac/adi,ad3552r.yaml.

Example (from the AXI DAC binding):

#include <dt-bindings/gpio/gpio.h>

axi_dac: spi@44a70000 {
    compatible = "adi,axi-ad3552r";
    reg = <0x44a70000 0x1000>;
    dmas = <&dac_tx_dma 0>;
    dma-names = "tx";
    #io-backend-cells = <0>;
    clocks = <&clkc 15>, <&ref_clk>;
    clock-names = "s_axi_aclk", "dac_clk";

    #address-cells = <1>;
    #size-cells = <0>;

    dac@0 {
        compatible = "adi,ad3552r";
        reg = <0>;
        reset-gpios = <&gpio0 92 GPIO_ACTIVE_HIGH>;
        io-backends = <&axi_dac>;
        spi-max-frequency = <20000000>;

        #address-cells = <1>;
        #size-cells = <0>;

        channel@0 {
            reg = <0>;
            adi,output-range-microvolt = <(-10000000) (10000000)>;
        };
    };
};

Function	File
EVAL-AD3552R Device Tree	arch/arm/boot/dts/xilinx/zynq-zed-adv7511-ad3552r-hs.dts

Driver testing

Each and every IIO device, typically a hardware chip, has a device folder under /sys/bus/iio/devices/iio:deviceX. Where X is the IIO index of the device. Under every of these directory folders reside a set of files, depending on the characteristics and features of the hardware device in question. These files are consistently generalized and documented in the IIO ABI documentation. In order to determine which IIO deviceX corresponds to which hardware device, the user can read the name file /sys/bus/iio/devices/iio:deviceX/name. In case the sequence in which the iio device drivers are loaded/registered is constant, the numbering is constant and may be known in advance.

Identify the device

The IIO device name is ad3552r for all supported variants.

root:/sys/bus/iio/devices/iio:device1> cat name
ad3552r

Channel attributes

Each of the two output channels exposes:

out_voltageN_raw: DAC code. Writes are rejected with EBUSY while the buffer is enabled.
out_voltageN_scale, out_voltageN_offset: Conversion to millivolts, (raw + offset) * scale, derived from the configured output range.
out_voltageN_sampling_frequency: Read-only streaming sample rate, in Hz. It is computed from the dac_clk rate and the number of SPI data lanes: dac_clk / 4 for the quad-SPI AD3551R/AD3552R and dac_clk / 8 for the dual-SPI AD3541R/AD3542R. Writes return EINVAL.

Data source (debugfs)

With CONFIG_DEBUG_FS enabled, data_source and data_source_available in /sys/kernel/debug/iio/iio:deviceX/ select the streamed data source, for example normal or ramp-16bit.

root:/sys/kernel/debug/iio/iio:device1# cat data_source
normal
root:/sys/kernel/debug/iio/iio:device1# echo -n ramp-16bit > data_source
root:/sys/kernel/debug/iio/iio:device1# cat data_source
ramp-16bit