Comedi driver for RPi ai, ao gpio for the gertboard daq_gert.c Driver: "experimental" daq_gert in progress ... for 4.1+ kernels with DT on the RPi2 with the bcm2835 SPI master with async Comedi commands and triggers The single processor version for the RPi has only the sync analog sample capability

Device-tree operation: Use overlay rpi-spigert-overlay.dtb to load the device module in /boot/config.txt: dtparam=spi=on dtoverlay=rpi-spigert-overlay.dtb

The DAQ-GERT appears in Comedi as a digital I/O subdevice (0) with 17 or 21 or 30 channels, a analog input subdevice (1) with a Mux for bipolar input voltages 2 differential-ended channels: (0) inputs 0-1, (1) inputs 2-3 2 single-ended channels: (2) (3) for inputs 2 or 3 a internal short of inputs for a offset reading: (4) with the ADC1220 adc, OR a analog input subdevice (1) with 2 single-ended channels with onboard adc, OR a analog input subdevice (1) with single-ended channels set by the SPI slave device and a analog output subdevice(2) with 2 channels with onboard dac

It's mainly a test driver for a modded version of xoscope in COMEDI mode

Current Status: Most of the DIO basics work but not totally correctly and speed on ADC samples is limited to about 20,000 S/sec on a RPi2

Notes: This driver currently requires a kernel patch to gain direct SPI access at the kernel level with an optional cs_change_usecs patch to spi.c and spi.h needed to reduce delays in cs_change=true transfers comment out #define CS_CHANGE_USECS in the daq_gert.c source if you don't use this part of the patch

• git clone https://github.com/raspberrypi/linux.git in /usr/src for the latest
• linux kernel source tree
• cd to the linux kernel source directory: /usr/src/linux etc...
• copy the daq_gert.diff patch file from the daq_gert directory to the source
• directory
• copy RPi2.config_4.1.y from the daq_gert directory to .config in the Linux source directory
• or
• copy RPi.config_4.1.y from the daq_gert directory to .config in the Linux source directory
• patch the kernel source with the daq_gert.diff patch file
• patch -p1 <daq_gert.diff
• copy the daq_gert.c source file to drivers/staging/comedi/drivers
• edit the /boot/config.txt file to add dtoverlay=rpi-spigert-overlay.dtb
• so on boot the system will disable the spi_dev protocol interface and use the spigert protocol instead
• make menuconfig or xconfig
• select SPI_COMEDI=m and SPI_DEV =m in SPI MASTERS to enable the SPI side of the driver
• select DAQ_GERT=m to select the Comedi protocol part of the driver in the
• staging daq comedi misc drivers section.
• make -j4 for a RPi 2 to compile a new kernel and driver in much less time
• use the instructions here to build the new kernel, modules, device-trees and overlays.
• https://www.raspberrypi.org/documentation/linux/kernel/building.md
• after the reboot: daq_gert should auto-load to device /dev/comedi0*
• if the legacy option is set in /etc/modprobe.d/comedi.conf the new device will be created after those
• dmesg should see the kernel module messages from daq_gert
• run the test program: bmc_test_program to see if it's working

The input range is 0 to 1023/4095 for 0.0 to 3.3(Vdd) onboard devices, 2.048 volts/Vdd for PIC slaves or +-0.512, +-1.024, +-2.048 for the ADS1220 device with usable range in double %2.6fV format for output The output range is 0 to 4095 for 0.0 to 2.048 onboard devices (output resolution depends on the device)

• In the async command mode transfers can be handled in HUNK mode by creating a SPI message
• of many conversion sequences into one message, this allows for close to native driver wire-speed

Analog: The type and resolution of the onboard ADC/DAC chips are set by the module option variable daqgert_conf in the /etc/modprobe.d directory

• options daq_gert daqgert_conf=1 gert_autoload=1

daqgert_conf options: 0 = Factory Gertboard configuratin of MCP3002 ADC and MCP4802 ADC: 10bit in/8bit out 1 = MCP3202 ADC and MCP4822 DAC: 12bit in/12bit out 2 = MCP3002 ADC and MCP4822 DAC: 10bit in/12bit out 3 = MCP3202 ADC and MCP4802 DAC: 12bit in/8bit out 4 = ADS1220 ADC and MCP4822 DAC: 24bit in/12bit out

gert_autolocal options: 0 = don't autoload (mainly for testing) 1 = load and configure daq_gert on boot (default)

All modules parameters can read in /sys/module/daq_gert/parameters

Comments: Things are looking pretty good for the MCP3X02 ADC driver section of the code. I can get a 30usec per sample avg over a 1 second burst period using xoscope with 26usecs for wire-speed and ~5 for CPU overhead without DMA for 12bit reads. Without DMA the output data stream is not totally continuous at full speed as I have to stop the SPI transfer to process and copy data (about 500us to process 1000 samples). With a driver request for less than full speed sample rates the software inserts calculated delays between samples (or groups of samples during a two channel scan) to adjust the sample to the correct time-splice.

• PIC Slave Info: Currently on runs in a slow polled mode with the PIC18 but the plan is to offload commands to it with a PIC24 version with 12bit samples at much higher speeds and auto sequencing.

• ADS1220 mode is for slow ~20 Sps of low level analog data