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mission:tech:odyssey:pdu [2012/10/05 17:49]
chrono [Software]
mission:tech:odyssey:pdu [2014/04/05 16:35]
chrono [Video]
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 +~~NOCACHE~~
  
 +====== Power Distribution Unit (PDU) ======
 +
 +The PDU is designed to efficiently convert electrical energy for three main power bus lines: 12V, 5V and 3.3V. This was done to overcome the problem of having to deal with inefficient power-converters found in many industry produced off-the-shelf components, used in the various application cases all over Apollo-NG's infrastructure. 
 +
 +The idea is to have modular, bus-controlled, point-of-load conversion modules for remote systems and to use the PDU's highly-efficient (>90%) buck/boost converters to supply the MCU, Storage-Devices, Audio, Communications- and Navigation-Equipment and all other hardware in close vicinity of the System-Module-Rack (SMR). 
 +
 +All devices are fed directly from the PDU, bypassing the on-board converters, thereby increasing the overall efficiency.
 +
 +===== Specs =====
 +
 +[{{:mission:tech:odyssey:pdu-overview.png?645}}]
 +
 +~~CL~~
 +
 +  * Input: 7-18V
 +  * Output:
 +    * 12V/5A > 95% Efficiency
 +    * 5V/5A >= 91% Efficiency
 +    * 3.3V/5A >= 93% Efficiency
 +  * Overcurrent Protection
 +  * In-Vehicle Protection
 +  * Monitoring:
 +    * Voltage (Input/12V/5V/3.3V)
 +    * Current (Input)
 +    * Temperature
 +  * Costs to operate: 0.5W
 +  * Operational Temperature: -25°C to +75°C
 +===== Main Power Busses =====
 +
 +==== 12V ====
 +
 +
 +==== 5V ====
 +
 +
 +==== 3.3V ====
 +
 +
 +===== Interface =====
 +
 +==== Sensors ====
 +
 +  * Allegro ACS715LLCTR-30A-T Hall effect-based linear current sensor
 +  * Power Supply, 12V, 5V & 3.3V Voltage Monitoring
 +  * DS18S20 Temperature sensor
 +
 +==== Controller ====
 +
 +AVR ATmega88
 +
 +==== Software ====
 +
 +The protocol and software were developed with a strong focus on security/reliability, very low system requirements and enough room for future options and modifications. The software package in the git repo consists of two parts.
 +
 +=== ATmega88 Firmware (and sources) ===
 +
 +Developed and tested with GCC
 +
 +=== PDUD - PDU Daemon (Python)  ===
 +
 +In order to keep the system impact on the SKU at a minimum, a polling system was out of the question. Luckily the Linux kernel supports inotify, as does python, which made the development of an inotify-event driven system very easy. 
 +
 +  * Kernel iNotifier watching changes in /var/state/apollo/odyssey/pdu/*
 +  * Wake on Change Interrupt routine:
 +    * Read changed value
 +    * Validate value
 +    * Check dependencies
 +    * Execute command on PDU
 +    * Go to sleep again
 +  * Periodically collecting and updating bus voltages, temperature and power consumption
 +
 +
 +==== Protocol ====
 +
 +
 +=== Command Frames ===
 +
 +The following tables show the protocol structure with example data:
 +
 +** Command-Request Frame**
 +
 +8 byte frame length
 +
 +^ Byte ^  0  ^  1  ^  2  ^  3  ^  4  ^  5  ^  6  ^  7  ^ 
 +| Def.|  Frame Begin (FB)  |  Bus Device Adress (BDA)  |  CMD  |  P1  |  P2  |  P3  |  CHK  | Frame End (FE)  | 
 +| DATA |  0xFB  |  0x10  |  0xCA  |  0xFF  |  0x00  |  0x00  |  0xB4  |  0xFE  |
 +
 +** Command-Response Frame **
 +
 +4 byte frame length
 +
 +^ Byte ^  0  ^  1  ^  2  ^  3  ^
 +| Def.|  Bus Device Adress (BDA)  |  R1  |  R2  |  CHK  |
 +| DATA |  0x10  |  0xFF  |  0x00  |  0x79  |
 +
 +
 +=== Data Frames ===
 +
 +** Data-Request Frame**
 +
 +8 byte frame length
 +
 +^ Byte ^  0  ^  1  ^  2  ^  3  ^  4  ^  5  ^  6  ^  7  ^ 
 +| Def.|  Frame Begin (FB)  |  Bus Device Adress (BDA)  |  CMD  |  P1  |  P2  |  P3  |  CHK  | Frame End (FE)  | 
 +| DATA |  0xFB  |  0x10  |  0xDA  |  0x00  |  0x00  |  0x00  |  0xA7  |  0xFE  |
 +
 +** Data-Response Frame **
 +
 +13 byte frame length
 +
 +^ Byte ^  0  ^  1  ^  2  ^  3  ^  4  ^  5  ^  6  ^  7  ^  8  ^  9  ^  10  ^  11  ^  12  ^
 +| Def.|  BDA  |  Loops  |  PDU_I  ||  PDU_U  ||  PSU_U  ||  PS5_U  ||  PS3_U  ||  CHK  |
 +| DATA |  0x10  |  0x59  |  0xC3  |  0x56  |  0xA2  |  0x97  |  0x23  |  0x42  |  0x08  |  0x15  |  0xE1  |  0xFA  |  0xCC  |
 +
 +
 +=== On the wire ===
 +
 +These DSO screenshots show the protocol on the wire: The left and middle image show different command-request (green) and command-response (yellow) frames, the right image shows a data-request (green) and data-response (yellow) frame. The latency for command execution is virtually non-existant (0.4ms), data-requests take a little more time to collect (2.5ms), this is due to the 13 byte framelength - it takes the ATmega a bit more time to calculate the checksum of the larger frame.
 +
 +{{:mission:tech:odyssey:pdu_protocol.png?208|}}
 +{{:mission:tech:odyssey:pdu_protocol1.png?208|}}
 +{{:mission:tech:odyssey:pdu_protocol2.png?208|}}
 +===== Operational Readiness Test (ORT) =====
 +
 +==== ORT Specs ====
 +
 +** Required tests to pass ORT **
 +
 +  * Uptime > 30 days without any erratic behaviour
 +  * Toggle PSU's in a 3 second interval for 96 hours without any erratic behaviour
 +  * Accurate results of temp/voltage/current sensors over time
 +  * Stable RS-232 signal quality 
 +  * Low host-system impact of PDU daemon
 +
 +** Results **
 +
 +All tests passed without a glitch, the system works as designed, com signals are solid and the system impact of the PDU Daemon on the host is almost non-existent, due to its use of kernel inotifiers (see the video for a time lapsed summary).
 +
 +==== Video ====
 +
 +{{mission:tech:odyssey:pdu_readiness_test3-640p.webm|}}
 +===== Repository =====
 +
 +Grab the latest code and all related files:
 +
 +<WRAP round download>
 +**Anonymous GIT Access**\\
 +//git clone [[git://apollo.open-resource.org/pdu]]//
 +</WRAP>
 +
 +
 +<WRAP round tip>
 +If you want to add files or commit changes, send your work to the ops-team or apply for git RW access by sending your pub-key to the ops-team.
 +</WRAP>