Sunday, October 22, 2017

OrangePI Zero overlay and uboot/armbian

The Armbian has good documentation about how to use device overlays for their uboot scripts.  I wanted to dive a little deeper and understand some of the basics and still use buildroot.

Boot process of uboot, there is a file on the FAT partition boot.src, this is a binary file generated by mkimage.  The source file is in board/orangepi/orangepi-zero
setenv fdt_high ffffffff
setenv load_addr "0x44000000"
echo "Boot script loaded from ${devtype}"

setenv bootargs console=ttyS0,115200 earlyprintk root=/dev/mmcblk0p2 rootwait

fatload mmc 0 $kernel_addr_r zImage
fatload mmc 0 $fdt_addr_r sun8i-h2-plus-orangepi-zero.dtb
fdt addr ${fdt_addr_r}
fdt resize 65536
setenv processorName sun8i-h3-
setenv overlays i2c0  spi-spidev
for overlay_file in ${overlays}; do
    echo " looking for  ${processorName}${overlay_file}.dtbo"
    if fatload mmc 0 ${load_addr} ${processorName}${overlay_file}.dtbo; then
        echo "Applying user provided DT overlay ${overlay_file}.dtbo"
        fdt apply ${load_addr} || setenv overlay_error "true"

bootz $kernel_addr_r - $fdt_addr_r

So, what happens is the device tree overlays are merged in uboot with the dtb file loaded for the board using fdt command line tools.  This allows to change the board dtb without always recompiling it.

Post any questions you have.   So, spi and i2c are now using device tree overlays.

Here is the overlay for SPI:

/ {
    compatible = "allwinner,sun8i-h3";

    fragment@0 {
        target-path = "/aliases";
        __overlay__ {
            spi0 = "/soc/spi@01c68000";
            spi1 = "/soc/spi@01c69000";

    fragment@1 {
        target = <&spi0>;
        __overlay__ {

            #address-cells = <1>;
            #size-cells = <0>;
            status = "disabled";

            spidev@1 {
                compatible = "linux,spidev";
                reg = <0>;
                spi-max-frequency = <1000000>;

    fragment@2 {
        target = <&spi1>;
        __overlay__ {

            #address-cells = <1>;
            #size-cells = <0>;
            status = "okay";

            spidev@2 {
                compatible = "linux,spidev";
                reg = <0>;
                spi-max-frequency = <25000000>;

so, this completes the task of using overlays.  Next DHCP and zeroconfig.

Also, have a modification to EEM USB handler, to improve performance.  Also, thinking of adding a way to use several packets at once based on the size of the packet.

Sunday, October 15, 2017

Merge latest changes from Cleanflight

Updated the repo with the latest CleanFlight changes, the merge compiled and ran on x86.  I'm in the middle of updating OrangePI buildroot to use some patches from Armbian and start using device tree overlays.  This makes it easier to add I2C etc without changing the orangePI zero DTS. More on that in the next couple of posts.  i.e basic device overlays using uboot via fdt commands.

Cleanflight configurator is working, the imu processing was not enabled, so, now the graphic is now updating.  

Also move the process to a core, using cpu isolation   (via taskset, etc) to reduce jitter.

Also, working on using dnsmasq as a dhcp server with mdev, this allows I/O board to get a IP address and try zeroconfig/DNS-Based Service Discovery.  The goal is to use names, instead of hard coded IP addresses, so when moving to WiFi networking there will not be a conflict.   Confusing?  I'm too ;)

Updated the I/O EEM packet handling to increase the performance, takes about 23us per 64 byte USB packet.  The goal is to have a 512 UDP packet take less then a 1ms. 

Looked at the GPS handling, right now, GPS parsing is handled on the I/O card, tho goal being to reduce processing in the main loop.  Still looking at the code and how RTH and stabilization process the GPS information.

Tasks Order:
  • Update Kernel/u-boot to use overlays
    • 4.13 kernel is booting along with u-boot (Now)
    • updating boot.src to process device tree overlays  (in progress)
  • Dynamic IP addressing 
    • Test DHCP server first
    • Add zeroconfig with MDNS on lwIP 
  •  Retest EEM USB Ethernet
  • Add LED API 
    • Cleanflight uses two LED APIs will use the basic one, i.e 3 LEDs and test the speed of UDP updating LEDs from Linux
  • Add PWM reciever API
    • The I/O is processing PWM from receiver, will forward this info onto Cleanflight  validate the configurator is working.

Sunday, September 17, 2017

Cleanflight repo updated with OrangePI Zero Flight Controller

Updated repo with current code for the OrangePI flight controller.
  • Replaced the cleanflight scheduler with libevent
    • all timers are based on libevent timers
    • in process of adding events for:
      • serial port
      • sockets
      • remote transmitters
    • Instead of using hard timers for the above events, timer is more of a timeout/guard.  The event, will be posted to wake up the task instead of a timer/poll event.  
    • For logging this will be moved into another thread using a message   So, sdcard write will not delay main processing loop, 
 Adding exti (external gpio interrupts).  Creating separate read file descriptors for each IO then push each one to libevent.  This way, when IO triggers libevent will dispatch the proper handler.   See if 4Khz is possible.

using top:
143   134 root     S     5804   1%   0% ./obj/main/cleanflight_LINUX.elf

Also added a command allowing to get basic info:

Task list             rate/hz  max/us  avg/us maxload avgload     total/ms
00 - (         SYSTEM)     10       2       1    0.5%    0.5%         0
01 - (            PID)     50     151     125    1.2%    1.1%        96
   - (           GYRO)    101
02 - (          ACCEL)    101     140     120    1.9%    1.7%        95
03 - (       ATTITUDE)    101       5       2    0.5%    0.5%         1
04 - (             RX)     50      18      10    0.5%    0.5%         4
05 - (         SERIAL)    101      12       2    0.6%    0.5%         1
06 - (       DISPATCH)
08 - (BATTERY_CURRENT)     50       1       0    0.5%    0.0%         0
09 - ( BATTERY_ALERTS)      4       4       1    0.5%    0.5%         0
10 - (            GPS)
11 - (        COMPASS)
12 - (           BARO)
13 - (       ALTITUDE)
14 - (      TELEMETRY)    101       1       1    0.5%    0.5%         0
15 - (        RCSPLIT)
RX Check Function                   0       0                         0
Total (excluding SERIAL)                         6.1%    5.3%

 I have to look into why some of the numbers a little high for PID and ACCEL.  Also add memory locking and add high FIFO scheduling.  But, looking good.

Sunday, August 27, 2017

CleanFlight update to Linux

Making slow progress, on updating CleanFlight to access SPI, I2C and serial port on Linux.

  • Updating bus_spi_linux.c to support SPI.
    • Still updating access functions based on previous work using LinuxFlight
  • Update scheduler to use libevent
    • Some of the issues with the current scheduler:
      • Does not use events, but polling for status for event block
      • Uses it's own timer framework
    • Created a new scheduler based on libevent
      • Using libevent timer framework
      • Adding a way for HW events and SW events to trigger a fc_task to wake.
        • Need some way to schedule based on priority, but will put this off, due progessing loop will not pause very long to progress a event, execept for I2C and SPI events.  Will change this next round to have another HW scheduling thread.
  • Need to branch LinuxFlight and push the new round of changes to to github.  With the support of SITL in cleanflight, minimal changes are needed. 
IO Board:
  • UDP via USB is not the fastest, about 500us for a 512 byte packet.  The main issue is full speed USB uses 64 bytes per interrupt.  So, it takes 8 USB packets to transfer one UDP 512 packet.  Once micro-controllers move to high speed USB, then USB packet is 512 bytes. 
  • Able to decode PWM signals
  • logging framework is done.

Sunday, July 30, 2017

General C/C++ lambda's and calling C code before main

I've been working on a few small projects, EtherCAT and QuadCopter IO board with USB EEM using STM32 micro-controllers. During this projects found couple interesting C++/C concepts:

  • Using Lambda functions for C callbacks
    • Simplifies static C++ functions to allowing C to call a C++ functions.
  • using GCC init to invoke C functions from C++ initialization.
    • One issue in creating projects is how to control or startup threads, init code etc in the proper order without #include every function.

Lambda Functions for C callbacks

lwIP has an asynchronous interface allowing the programmer not to create a thread to wait on socket events, all of the events occur within lwIP worker thread.  Using the same thread alleviates locking

err_t            tcp_connect (struct tcp_pcb *pcb, const ip_addr_t *ipaddr,
                              u16_t port, tcp_connected_fn connected);

The above function starts the TCP connection with the IP address in the function.  So, function requires a C callback function.  

 err = tcp_connect(m_conn, &ipaddr, PORT, [](void *arg, struct tcp_pcb *tpcb, err_t err) -> err_t
                                              class *pToClass = reinterpret_cast<class *>(args));
                                              return pToClass->connect(tpcb, err);

From the code above, a lambda is used without any capture arguments, this allows the lambda to be callable from C.  So, now the connect function can also be a protected function.  So, no static function needs to be declared. 

Using C++ constructor to invoke a C function before main

Here is a simple function:

static void _startUpUdpServices(void) __attribute__((constructor (102)));
void _startUpUdpServices(void) 

    regStartUpFunction(StartUpPriority::_6, "udpServices", (startUpFunctor_t)startUpUDPServices);

The __attribute__((constructor (102))); Puts the function in the .init section and orders it to be at 102.  So _startUpUdpServices function will be called before main.  This makes it easy to register a system without calling the function.  nothing is worse then spegitti code to debug.  Now, it is possible to order using higher numbers.  I took a little more time and create anoterh class to register function and order them.

If you have any questions let me know...

Sunday, June 25, 2017

Update ( dRonin communication to secondary board via UDP (USB EEM))

EEM USB is now working, there are some performance tweaks still needed, but, it is working.

Next start on a simple protocol to setup pins and pwm modes, ie, oneshot, or pwm out.  The goal is to use micropython and json for pin maping, and have a work task handle the I/O.  

Next week, will checkout TCP performance using iperf and Lwip netperf app.

Pushing forward.  

Thursday, May 25, 2017

dRonin communication to secondary board via UDP (USB EEM)

There is a similar project, called FlyingPI, but instead of using Raspberry PI, this project is using the OrangePI (Zero)/(Zero plus2) 

The interface between the micro-controller and flight controller will be USB (Full-Speed).  (Soon there will be STM32 high speed USB  boards out, but as of now, it is USB Full Speed).  The protocol will be EEM-USB (Ethernet-Emulation-Model), it is simple, just two bulk end-points.  At this time I have a basic STM class driver setup and some what talking to Linux.   An Ethernet interface is created and DHCP messages are streaming from the Linux. So, at-least the USB descriptors are working etc.

Why use USB?  Why use Ethernet? The goal is to make the flight controller interface generic, i.e UDP This way different boards or platforms can use standard sockets instead of SPI, Serial, etc. 

The main issue at this time is RAM space the board only has 138K of RAM, so, buffer space will be limited, but, should work.

Moving forward...