K9 SmorgasBoard Overview Rev 1

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1 K9 SmorgasBoard Overview Rev 1 June 7 th 2013 For several weeks, Steve Stallings (Practical Micro Design, Inc.) and I (David Bagby, Calypso Ventures, Inc.) have been collaborating to create a LCNC embedded system development multi-tool: The K9 SmorgasBoard. This paper provides an overview of the K9 SmorgasBoard (K9). The information herein will mostly be of interest to those doing development work for LCNC on Beaglebones. 1 Motivation For some time Steve and I have both had an interest in the potential of using a SoC approach as an embedded LCNC control platform and I d been looking at using a Beaglebone for this. We d kicked the idea for this project around at several times in the past, but it never quite got started. The more recent release of the BBB (Beaglebone Black) shifted the BB price/performance ratio, and that generated enough impetus to make this project happen. The K9 SmorgasBoard is intended as a LCNC embedded system developer s platform. As such, it contains one-off features that would not be practical in an end user product (those things that your inner hardware/software engineer wants to play with but can t justify creating a dedicated cape for). We decided to create a developer s tool to help soften up the BBB. The idea is to make various BBB subsystems easily available for hardware and software prototyping work. We hope this will complement the LCNC BBW software work others have been doing, and facilitate the LCNC BBW to BBB transition. 2 K9 Design Goals: While reading this paper, it may help to refer to this high level block diagram of a BBB/K9 system: Page 1 of 11

2 K9 SmorgasBoard Beaglebone (black or white) P8 & P9 access, buffering, isolation, level shifts CPLD PP Interfaces (3) Other proto interfaces Power control, board config Existing BoB(s) Engineer s bench play things Figure 1: BB/K9 block diagram 2.1 A Developer s Platform We specifically wanted to create a developer s platform. I.E. a tool that would facilitate additional software and hardware development. The K9 board is not intended, nor designed, to be a commercial end user product. Ignoring commercial considerations allowed us to ignore things like PCB size, BOM cost and ROI in favor of a short design cycle. Frankly, we ve tried not to add up the BOM cost; we d rather now know. Instead, blissful ignorance and the limited build run enables K9 feature largesse. The K9 board is about 8 x6. The over-cape size allows easy developer access to all test points etc. 2.2 Calendar date driven design We decided that whatever feature set we ended up having, it had to be doable before the 2013 Wichita LCNC fest. We wanted to be able to share the K9 during that week. This goal placed practical constraints on the features that could be included. For this project, Doable was defined to mean that the board would be designed, and a small number (single digits) built & populated. Page 2 of 11

3 The adopted schedule meant there would be only one shot at this. We hope to debug the hardware before Wichita, but we may end up doing K9 first power up during that week. 2.3 Design Flexibility The short time frame mandated flexibility in the design. The BBB is new and we re seeing the usual new product teething issues with the BBB. A design approach around a CPLD was chosen. This let the PCB, CPLD and software design overlap. It also provides significant flexibility since different CPLD loads can radically reconfigure the board. We expect to have the initial (stock) CLPD load ready for use in Wichita. For LCNC, the stock CPLD load provides BBB direct PRU interfacing without impacting the emmc or HDMI video subsystems Multi-Bone flavors The primary design goal is the BBB. However, the K9 was also designed to work with the BBW. The BBB emmc and HDMI Video features are still available when using the K9 with a BBB (HDMI audio lines are repurposed for K9 use). With a BBW it is possible to configure the board so that all the P8 & P9 pins are available to the K Bone protection The K9 provides reasonable protection for the BBB by providing level shifting and impedance protection to the Beaglebone. The outside world signals are 3.3 volt CMOS levels but are 5 volt tolerant. Hardware experimentation may blow portions of the K9, but the Beaglebone should be isolated enough (we hope) to survive. 2.4 Real Machine Capability A key goal is be able to use a K9/BBB combination to drive real machines. This meant that we included BB specific feature support, and did not want to replicate common breakout board (BoB) functionality within the K9. We chose to use ribbon cables with parallel port (PP) pin assignments to allow simple direct connection to existing PP oriented BoBs Stepper Machine Centric For the initial K9 we decided to focus on open loop stepper driven machines. The K9 also includes hardware features which enable developers to evaluate further the practicality of driving servo machines with encoders from the BBB (with or without additional external hardware support). Page 3 of 11

4 2.4.2 Typical Axis Mill The K9 will handle a 4 axis + spindle mill, including reasonable GPIO, via one PP cable to a BoB. With a 2 PP cable interface, significant additional IO is available D Printers In addition to the required digital axes, the K9 has support for the analog features necessary to drive a typical 3D extrusion printer. The K9 s BBB analog features are not routed thru a PP interface header, instead they are available directly on K9 connectors Full 9 Axis LCNC System The K9 can drive 9 axes (S&D) from either BBB GPIO or PRU direct IO connections. The use of axes B-W requires the use of 2 PP interface cables. 2.5 K9 Project Documentation & Status This paper is a slight pretty up of our informal design notes. Embedded LCNC developers will need to be familiar with key references, including the BBB SRM, the AM335x TRM and various other specs used in the design of the K9. The standard disclaimer applies: Anything in this document, the K9 or anything related to it, is subject to change at any time, and without notice. Hey, what did you expect for a developer s BBB/LCNC multi-tool? 3 K9 Interfaces The K9/BBB provides access to all the major BBB subsystems. 3.1 BBB/BBW Connections P8 & P9 The BBB mounts (upside down) onto the K9. All P8 and P9 signals from the BB are available to the K9 (and most are routed into the CPLD). From the CPLD signals are sent to the outside world via K9 interface connectors. Push buttons on the BB are duplicated on the K9 for easy access. To achieve compatibility with both the BBB and BBW the K9 can be configured to disconnect itself form the BBB pins used for the emmc. There are test points for all pins on P8 & P9. P8 & P9 signals are impedance protected and buffered to 5V tolerant interfaces on the K9 (K8 provides 3.3v output drive with 5V tolerant inputs). Page 4 of 11

5 The K9 does not support the stacking of another BB cape with the K9. The physical aspects of this were difficult (the BBB is upside down on the K9) and the necessary (pass thru) connectors were not readily available within the target time frame. Additionally, the K9 already utilizes every pin available on P8 & P Alternate Boot Configuration support The K9 can set any combination of SYSBoot pins during the boot process. This allows experimentation with alternate BB boot code sources User LEDs The BB User LEDs are not available on a BB connector and thus they are only present on the BB itself. There is a reflective surface under the BBB User LEDs to allow viewing of the User LEDs from above Serial Console (3.3v FTDI connector) The BB serial console connector is routed to a duplicate K9 connector so that the console output is still accessible when the BBB is mounted on the K Bone JTAG The Bone JTAG connection are physically on the bottom of the bones. The Bone s upside down mounting to the K9 makes this accessible when using a K BBB & K9 Power Options K9 powered via BBB The K9 can be powered from the BBB. For a typical setup, no additional power supply is required. When the K9 is powered from an external 5V/2A supply, the K9 has up to 1.5A available (limited by the BBB power supply in use, and connector capacity). A 2A 5V supply for the BBB is recommended. Note: It is NOT reasonable to power the BBB/K9 combo ONLY from a PC via the USB cable. The USB cable can only supply a limited USB current capacity and the BBB draws close to the USB max of 500ma; leaving nothing for the K BBB powered via K9 The BBB can also be powered via K9 connectors. There is both a BBB compatible barrel connector on the K9 and a terminal strip for external K9 power (both 5V). The K9 power inputs have modest reverse voltage protection. Page 5 of 11

6 There is a system on/off switch on the K9 so that you do not have to unplug the power jacks to really power down. The power system has indicators for Input power present to system (a post power switch indication). K9/BBB System is powered up. This indicates that all power sequencing is complete and the entire BBB/K9 system is powered up. The normal soft power switching using the Power button still functions and will control power of both the Bone and the K BBB / K9 power interfacing The K9 takes care of BBB power interfacing and power sequencing issues. Do not use both a K9 external power source and an external BBB power source. Unless the supplies are exactly matched, one will drive power into the other. The K9 has a local (BBB sequenced) 3.3v supply rail. This allows the K9 to not burden the BBB 3.3v supply. The K9 has reset line support to correct some problems (pulse width specs) recently noted in the BBB community. A K9/BBB can be reset by Push button (BBB reset line) K9 voltage monitor (checks input 5V power rail) Watch dog capability (experimental) 3.3 PP BoB Connections The grouping of IP signals onto PP headers can be altered with different CPLD loads. The initial K9 CPLD design configuration is: PP1: Common 4 axis machine to PP BoB 4 axis S&D (PRU EGPIO) Spindle control General IO Pin allocations match the default signal arrangements for a PMDX-126 BoB (port 1). PP2: BB subsystem prototyping Encoder testing using the ecap encoder support on the BBB PWM UARTs Page 6 of 11

7 I2C PP3: Axes 6-9, other IO subsystems 5 axis of S&D (PRU EGPIO) 2 EHRPWM (PWM outputs) 1 ecap (encoder) input Each of the PP cable signals are available as both ribbon headers and DB25s. This allows one to be used for interconnect and the other for test points. Thus every PP cable signal is available as a test point from the K9. Consult the schematics and detailed documentation for BBB P8/P9 to PP pin mappings. 3.4 K9 stock CPLD configuration 3.5 GPIO Effectively every digital signal from BBB P8 & P9 is an input to the CPLD. Therefore all signals are available as CPLD outputs (with an appropriate CPLD load). The stock K9 configuration muxes the Am335x so that most of the internal BB subsystems are accessible via the K9. There are sufficient GPIO pins still available to support multi-axis machines with reasonable IO requirements. 3.6 PRU The K9 design maximizes access to direct (PRU Enhanced GPIO signals) IO from PRU0 (and a few from PRU1). This is the expected mode of operation for an embedded LCNC K9/BBB system. The favoring of PRU0 is driven by the allocation of BBB pins to emmc and HDMI (which tend to use the PRU1 enhanced GPIO pins). Outputs driven by code written to use Am335x GPIOs will be slower than that using PRU EGPIOs, but can be accommodated by re-muxing the BBB pins (from K9 PRU EGPIO defaults to plain GPIO). This would require a change to the K9 eprom, device tree overlay and (maybe) a revised CPLD load. 3.7 Proto Toy Connections The K9 provides access to various Am335x internal subsystems. Access to these systems for prototype purposes is generally made via K9 terminal strips. The Am335x signals used will often also be routed to a PP header. Be careful not to set up multiple driving sources for a signal. Consult the schematics and detailed documentation as required ecap The K9 provides a differential encoder input that provides voltage level translation for the AM335x. The inputs are connected to one of the ecap subsystems. Page 7 of 11

8 This can be used to develop and evaluate software for encoder processing with the BBB. With sufficient cleverness and reuse of the RS422 receivers, a 2 nd encoder input might also be made available PWM An Enhanced PWM subsystem of the AM335x is brought out to the K9. This allows the developer to work with the EPWM system. Some of these are also routed off to high power buffers (see high power GPIO section) Serial Comms Two serial ports are available from the K9 (uart2 and uart4). All uart lines have external connector jumper disconnects. The Rx, Tx (and Gnd) signals (no handshaking signals) are available conditioned as follows: Uart2 RS232 on a DB9 Term strip with RS422 drivers. This is intended for external serial device interfacing and modbus support prototyping Uart4 RS 422 term strip One 6 pin header pinned out as a serial console header. This allows the use of a 3.3v ftdi cable to access this port. Three pin header with RS232 level Rx, Tx, Gnd signals I2C There is a buffered 5V I2C bus available on the K9 and several K9 components are interfaced to the I2C bus. The K9 I2C bus can be connected to one of two I2C busses of the AM335x: I2C2 (used by the BBB to read cape eprom contents) or I2C1 which is made generally available via the K SPI SPI busses are possible with the K9. However, they are not part of the default configuration. At a minimum a pin mux change will be needed to access an SPI bus (at the cost of losing access to what is already on those pins) Analog Input The K9 supports the Am335x analog input abilities as follows: 4 inputs (via K9 terminal strips) that can function as AM335x analog inputs. These can be used to read thermisters (they have pull ups to a known reference Page 8 of 11

9 voltage). The BBB inputs are K9 input protected. The range is nominally 0-1.8v (inputs are voltage clamped so really about a v usable range). 2 channels of analog input with thermocouple conditioning. Intended to be used as temperature measuring inputs. One Potentiometer input. This is a simple analog input from 0-1.8v (just to have something to read from in software without requiring any additional hardware) Analog Output The K9 provides a term header with 4 12bit DAC outputs. The DACs are I2C interfaced. Output range is 0-5v K9 CPLD programming There is a K9 CPLD programming jack (JTAG; 14 pin, 0.1 centers) RTC The BBs do not have a RTC with on board battery support. The K9 provides a RTC with battery back up (interfaced to the K9 I2C bus) GPIO Alternate Switch inputs There is a header to connect four switches between inputs and gnd. These are alternate inputs that duplicate the 4 inputs available on the first parallel port. They are provided so that users of the on board stepper drivers can complete a system without needing a separate breakout board. Weak pull-up resistors are provided High power GPIO Voltage limits for all K9 high current GPIO lines is 12v. This applies to the heater (PWM) and steppers motor driver interfaces only. All other GPIO signals are only 5v tolerant. Therefore, when using some K9 proto features, an external supply may be required (max 12v) to supply a higher voltage to interfaced components High Current PWM There are K9 terminal connections for outputs for two high current PWM controller outputs (heaters etc) Fan switching There are K9 terminal connections for two FET switches for DC fans or relay control Stepper motor driver sockets The K9 provides sockets and motor connectors for 4 Pololu style stepper motor drivers. These sockets are hooked to the X, Y, Z & A axes (as routed to PP1). Page 9 of 11

10 4 K9 Software support 4.1 BBB cape hardware support K9 Cape eprom The K9 includes a BB cape ID eprom. This eprom is BB cape ID and pin usage information for the K9. The information is used by the BB during boot time to configure BB cape pins Device Tree The K9 will have a Device tree overlay for use with the 3.8 kernel. This is in development and is expected to be ready in time for Wichita. 4.2 LCNC on BBB kernel considerations 4.3 Kernel impacts The BBB ships with a Linux 3.8 kernel. The K9 design targets the BBB and thus inherits the 3.8 kernel environment. The BBW ships with a 3.2 kernel. The K9 hardware is ignorant of the kernel in use and the hardware should just work on the BBW under 3.2. The default K9/BBB hardware setup should be fine under 3.2 on a BBW, it just won t access the emmc pins. To get access to these pin ranges, the K9 can be reconfigured (jumper switches) to also use the emmc pins BBB Disable Clock power management The BBW does not do CPU clock power management. So this is not an issue for the K9/BBW parings. The BBB has CPU clock fiddling enabled in the 3.8 kernel by default (the CPUY clock speed is a function of CPU load). This will create unwanted jitter in the system response. A recompiled Kernel (with CPU clock fiddling turned off) will be required for all BBB LCNC systems Device Tree A K9 specific DTB overlay will be provided with the K9 to match the CPLD load. Side note: Apparently the DTB compiler with overlay support only works on Angstrom out of the box. There are DT compiler patches that need to be applied if using Ubuntu or Debian. Page 10 of 11

11 4.3.3 PRU loading Under 3.2 there are some PRU loading drivers that have to be compiled into the kernel. The drivers are used to load code into the PRUs. See AM335x PRU Linux Application Driver (prussdrv.c) at This driver needs to be built into the 3.8 kernel in order to support PRU loading Xenomai The Xenomi patches for 3.8 appear to be available. As of when this was written, it s uncertain if anyone has built a BBB patched 3.8 kernel with all the requirements listed in this section. Page 11 of 11

Beaglebone green User Manual

Beaglebone green User Manual Release date: 2015/9/22 Version: 1.0 Wiki: http://www.seeedstudio.com/wiki/beaglebone_green Bazaar: http://www.seeedstudio.com/depot/beaglebone-green-p- 2504.html?cPath=122_113