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fpga

README.md

Directory structure

path contents
fpga/Makefile main Makefile, used to run FPGA related tools
fpga/*.tcl TCL scripts to be run inside FPGA tools
fpga/archive/ archive of XZ compressed FPGA bit files
fpga/doc/ documentation (block diagrams, address space, ...)
fpga/ip/ third party IP, for now Zynq block diagrams
fpga/rtl/ Verilog (SystemVerilog) "Register-Transfer Level"
fpga/sdc/ "Synopsys Design Constraints" contains Xilinx design constraints
fpga/sim/ simulation scripts
fpga/tbn/ Verilog (SystemVerilog) "test bench"
fpga/hsi/ "Hardware Software Interface" contains FSBL (First Stage Boot Loader) and DTS (Design Tree) builds

Build process

Xilinx Vivado 2015.4 (including SDK) is required. If installed at the default location, then the next command will properly configure system variables:

. /opt/Xilinx/Vivado/2015.4/settings64.sh

The default mode for building the FPGA is to run a TCL script inside Vivado. Non project mode is used, to avoid the generation of project files, which are too many and difficult to handle. This allows us to only place source files and scripts under version control.

The next scripts perform various tasks:

TCL script action
red_pitaya_hsi_dram_test.tcl should create the zynq_dram_test but the produced binary can not be run from a SD card
red_pitaya_hsi_dts.tcl creates device tree sources
red_pitaya_hsi_fsbl.tcl creates FSBL executable binary
red_pitaya_vivado_project.tcl creates a Vivado project for graphical editing
red_pitaya_vivado.tcl creates the bitstream and reports

To generate a bit file, reports, device tree and FSBL, run:

make

To generate and open a Vivado project using GUI, run:

make project

Device tree

Device tree is used by Linux to describe features and address space of memory mapped hardware attached to the CPU.

Running make inside this directory will create a device tree source and some include files:

device tree file contents
zynq-7000.dtsi description of peripherals inside PS (processing system)
pl.dtsi description of AXI attached peripherals inside PL (programmable logic)
system.dts description of all peripherals, includes the above *.dtsi files

To enable some Linux drivers (Ethernet, XADC, I2C EEPROM, SPI, GPIO and LED) the device tree source is patched using ../patches/devicetree.patch.

Signal mapping

XADC inputs

XADC input data can be accessed through the Linux IIO (Industrial IO) driver interface.

E2 con schematic ZYNQ p/n XADC in IIO filename measurement target range
AI0 AIF[PN]0 B19/A20 AD8 in_voltage11_raw general purpose 7.01V
AI1 AIF[PN]1 C20/B20 AD0 in_voltage9_raw general purpose 7.01V
AI2 AIF[PN]2 E17/D18 AD1 in_voltage10_raw general purpose 7.01V
AI3 AIF[PN]3 E18/E19 AD9 in_voltage12_raw general purpose 7.01V
AIF[PN]4 K9 /L10 AD in_voltage0_raw 5V power supply 12.2V

Input range

The default mounting intends for unipolar XADC inputs, which allow for observing only positive signals with a saturation range of 0V ~ 1V. There are additional voltage dividers use to extend this range up to the power supply voltage. It is possible to configure XADC inputs into a bipolar mode with a range of -0.5V ~ +0.5V, but it requires removing R273 and providing a 0.5V ~ 1V common voltage on the E2 connector.

NOTE: Unfortunately there is a design error, where the XADC input range in unipolar mode was thought to be 0V ~ 0.5V. Consequently the voltage dividers were miss designed for a range of double the supply voltage.

5V power supply

                         -------------------0  Vout
           ------------  |  ------------
 Vin  0----| 56.0kOHM |-----| 4.99kOHM |----0  GND
           ------------     ------------

Ratio: 4.99/(56.0+4.99)=0.0818 Range: 1V / ratio = 12.2V

General purpose inputs

                         -------------------0  Vout
           ------------  |  ------------
 Vin  0----| 30.0kOHM |-----| 4.99kOHM |----0  GND
           ------------     ------------

Ratio: 4.99/(30.0+4.99)=0.143 Range: 1V / ratio = 7.01

GPIO LEDs

LED color SW driver dedicated meaning
[7:0] yellow RP API user defined
[8] yellow kernel MIO[0] CPU heartbeat (user defined)
[9] reg kernel MIO[7] SD card access (user defined)
[10] green none "Power Good" status
[11] blue none FPGA programming "DONE"

For now only LED8 and LED9 are accessible using a kernel driver. LED [7:0] are not driven by a kernel driver, since the Linux GPIO/LED subsystem does not allow access to multiple pins simultaneously.

Linux access to GPIO

This document is used as reference: http://www.wiki.xilinx.com/Linux+GPIO+Driver

The base value of MIO GPIOs was determined to be 906.

redpitaya> find /sys/class/gpio/ -name gpiochip*
/sys/class/gpio/gpiochip906

GPIOs are accessible at base value + MIO index:

echo 906 > /sys/class/gpio/export
echo 913 > /sys/class/gpio/export

Linux access to LED

This document is used as reference: http://www.wiki.xilinx.com/Linux+GPIO+Driver

By providing GPIO/LED details in the device tree, it is possible to access LEDs using a dedicated kernel interface. NOTE: only LED 8 and LED 9 support this interface for now.

To show CPU load on LED 9 use:

echo heartbeat > /sys/class/leds/led9/trigger

To switch LED 8 on use:

echo 1 > /sys/class/leds/led8/brightness