rnd:projects:aft

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rnd:projects:aft [2022-12-21 07:01] – asdfrnd:projects:aft [2023-05-07 02:54] (current) – asdf
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 ==== SFP modules ==== ==== SFP modules ====
-SFPs (small form-factor pluggable) are compact IR transceivers designed for fiber optic networking. There are two major advantages to using an SFP in this device. First, it puts the tester on equal footing with the devices in the live environment. We don't have to worry about propagation distances; if the tester can't transmit over the entire fiber run, then neither will a switch be able to. Second, it allows the tester to check the SFP itself using DDM/DOM [(ddm_dom)] or I2C [(sfp_i2c)]. In the future, we may also be able to program the tester to talk to live network devices to help determine where the other end of the cable goes((It seems likely that an Arduino Uno is not fast enough to process Ethernet frames. One of the beefier boards may, but this feature is not essential for the tester as described.)).+SFPs (small form-factor pluggable) are compact IR transceivers designed for fiber optic networking. There are two major advantages to using an SFP in this device. First, it puts the tester on equal footing with the devices in the live environment. We don't have to worry about propagation distances; if the SFP-equipped tester can't transmit over the entire fiber run, then neither will a switch be able to. Second, it allows the tester to check the SFP itself using DDM/DOM [(ddm_dom)] or I2C [(sfp_i2c)]. In the future, we may also be able to program the tester to talk to live network devices to help determine where the other end of the cable goes((It seems likely that an Arduino Uno is not fast enough to process Ethernet frames. One of the beefier boards may, but this feature is not essential for the tester as described.)).
  
 The electrical pinout is shown in {{ref>tab_sfp_pinout}}. The electrical pinout is shown in {{ref>tab_sfp_pinout}}.
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 | 20 | VeeT | Transmitter ground | | 20 | VeeT | Transmitter ground |
 </table> </table>
 +
 +<WRAP center round tip 60%>
 +The ''Tx_disable'' pin is connected to an internal pull-up resistor inside the module. This pin must be pulled low to enable the transmit laser.
 +</WRAP>
  
 ==== Osmocom SPF experimenter ==== ==== Osmocom SPF experimenter ====
-For the prototypes, we will be using the Osmocom SFP Experimenter board. This breakout contains all support circuitry required to send single-ended signals through an SFP. No restriction is made on the input data, so we need not send valid Ethernet frames. That opens up the question of how we are to encode the data for transmission [(data_encoding)]. Of course, instead of sending arbitrary bits, we could instead transmit a clock. +For the prototypes, we will be using the Osmocom SFP Experimenter board. This breakout contains all support circuitry required to send single-ended signals through an SFP. No restriction is made on the input data, so we need not send valid Ethernet frames. <del>That opens up the question of how we are to encode the data for transmission [(data_encoding)]. Of course, instead of sending arbitrary bits, we could instead transmit a clock.</del> There's no need to encode the data ourselves---just use hardware UART pins.
  
 For whatever reason, the SFP Experimenter board is designed to accept I/O connections through SMA connectors (one per stream). The units ship without the connectors soldered to the board, so we can add whatever kind of interface we want---simple wires will do.  For whatever reason, the SFP Experimenter board is designed to accept I/O connections through SMA connectors (one per stream). The units ship without the connectors soldered to the board, so we can add whatever kind of interface we want---simple wires will do. 
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 SFP modules expose a great deal of data detailing their internal status, all accessible through I2C at one of two addresses (''0xA0'', ''0xA2''). Before data can be read, the EEPROM address must be loaded in by performing a dummy write containing the 8-bit EEPROM address to retrieve. For example, the device vendor name is stored in 16 bytes at I2C address ''0xA0'', EEPROM address 20. The following snippet demonstrates this procedure. SFP modules expose a great deal of data detailing their internal status, all accessible through I2C at one of two addresses (''0xA0'', ''0xA2''). Before data can be read, the EEPROM address must be loaded in by performing a dummy write containing the 8-bit EEPROM address to retrieve. For example, the device vendor name is stored in 16 bytes at I2C address ''0xA0'', EEPROM address 20. The following snippet demonstrates this procedure.
  
-<code c>+<code cpp>
 // load in the EEPROM address // load in the EEPROM address
 Wire.beginTransmission(0x50); Wire.beginTransmission(0x50);
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 After each read, the internal address register is incremented so it points to the next byte. Given the way we're most likely to access this table, this fact is of relatively little use to us. After each read, the internal address register is incremented so it points to the next byte. Given the way we're most likely to access this table, this fact is of relatively little use to us.
  
 +<table |tab_sfpreg_50>
 +<caption>Registers of interest at I2C address 0x50</caption>
 +
 +<datatables paging="false">
 +^ Value ^ Address (dec) ^ Data length ^
 +| Manufacturer name (ASCII) | 20 | 16 |
 +| Compliance code | 3 | 8 |
 +| Nominal signalling rate (100s Mbd) | 12 | 1 |
 +| Supported optional DDM features | 93 | 1 |
 +</datatables>
 +</table>
 +
 +<table |tab_sfpreg_51>
 +<caption>Registers of interest at I2C address 0x51</caption>
 +
 +<datatables paging="false">
 +^ Value ^ Address (dec) ^ Data length ^
 +
 +</datatables>
 +</table>
 ==== Serial data transmission ==== ==== Serial data transmission ====
  
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 We don't want to rely on the Osmocom SFP Experimenter board for the final product, but it has the major advantage of a built-in differential transmitter and receiver((If sending differential signals, must they be of the same magnitude? Can I send a clock into one side and the actual data into the other? Need to read more and possibly simulate this.)).  We don't want to rely on the Osmocom SFP Experimenter board for the final product, but it has the major advantage of a built-in differential transmitter and receiver((If sending differential signals, must they be of the same magnitude? Can I send a clock into one side and the actual data into the other? Need to read more and possibly simulate this.)). 
  
-{{ref>tab_pin_usage}} indicates proposed pin connections. Underlined items are ideally suited for interrupts.+{{ref>tab_pin_usage}} indicates proposed pin connections. Underlined items are ideally suited for interrupts((Since the controls will be operated at human speed, interrupts probably aren't necessary for the encoder.)).
  
 <table |tab_pin_usage> <table |tab_pin_usage>
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 | ^ Device pin ^ ^ Arduino pin ^ | ^ Device pin ^ ^ Arduino pin ^
 ^ LCD |||| ^ LCD ||||
-| | RX |  <-  | D8 |+| | RX |  <-  | D8 (''SoftwareSerial'') |
 | | +5V |  <-  | +5V | | | +5V |  <-  | +5V |
 | | GND |  <-  | GND | | | GND |  <-  | GND |
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 | | +3.3V |  <-  | +3.3V | | | +3.3V |  <-  | +3.3V |
 | | GND |  <-  | GND | | | GND |  <-  | GND |
-| | __RX__ |  ->  | | +| | __RX__ |  ->  | D0 (''Serial1'') | 
-| | TX |  <-  | | +| | TX |  <-  | D1 (''Serial1'') | 
-| | SDA |  <->  | SDA (D2) | +| | SDA |  <->  | SDA/D2 | 
-| | SCL |  <->  | SCL (D3) |+| | SCL |  <->  | SCL/D3 |
 | | TX_FAULT |  ->  | D5 | | | TX_FAULT |  ->  | D5 |
 | | MOD_ABS |  ->  | D4 | | | MOD_ABS |  ->  | D4 |
 ^ Rotary encoder |||| ^ Rotary encoder ||||
-| | __Enc A__ |  ->  | D0 | +| | __Enc A__ |  ->  | D18 | 
-| | __Enc B__ |  ->  | D1 |+| | __Enc B__ |  ->  | D19 |
 | | GND |  <-  | GND | | | GND |  <-  | GND |
-| | __Sw A__ |  ->  | D7 (''INPUT_PULLUP'') |+| | __Sw A__ |  ->  | D17 (''INPUT_PULLUP'') |
 | | Sw B | | GND | | | Sw B | | GND |
 </table> </table>
  
 +==== Communication ====
 +UART transmission is not looking terribly promising at this time. 
 +
 +Different SFP models appear to produce different signals when the output is open. The SMF unit (unknown vendor) outputs nothing, while the Veloso units send (noisy) pulse trains (see {{ref>fig_idle}}). They also respond differently to inputs, with the former producing an inverted replica of the input and the latter outputting what might be PWM ({{ref>fig_k}}).
 +
 +<figure center|fig_idle>
 + <subfigure |fig_smf_idle>
 + {{ :rnd:projects:smf-idle.png?400 |}}
 +<caption>SMF</caption>
 + </subfigure>
 + <subfigure |fig_veloso_idle>
 + {{ :rnd:projects:veloso-idle.png?400 |}}
 +<caption>Veloso</caption>
 + </subfigure>
 +<caption>Idle responses from signal loopback</caption>
 +</figure>
 +
 +<figure center|fig_k>
 + <subfigure |fig_smf_k>
 + {{ :rnd:projects:smf-k.png?400 |}}
 +<caption>SMF</caption>
 + </subfigure>
 + <subfigure |fig_veloso_k>
 + {{ :rnd:projects:veloso-k.png?400 |}}
 +<caption>Veloso</caption>
 + </subfigure>
 +<caption>Responses to UART ''k'' at 115200 baud, 8N1</caption>
 +</figure>
 ==== Power considerations ==== ==== Power considerations ====
 Portable operation is a must for this tester. Portable operation is a must for this tester.
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   * [[https://github.com/Stutchbury/EncoderButton]]   * [[https://github.com/Stutchbury/EncoderButton]]
   * [[https://www.instructables.com/Manchester-Code-Library-for-Arduino/]], [[https://github.com/mdeudon/Manchester]], [[wp>manchester code]]   * [[https://www.instructables.com/Manchester-Code-Library-for-Arduino/]], [[https://github.com/mdeudon/Manchester]], [[wp>manchester code]]
 +  * https://www.ti.com/lit/ug/tidu366/tidu366.pdf
 +  * https://cdn.hackaday.io/files/21599924091616/AN_2030_DDMI_for_SFP_Rev_E2.pdf
 +  * https://gitea.osmocom.org/electronics/osmo-small-hardware/raw/branch/master/sfp-breakout/sfp-experimenter.pdf
 +  * https://www.ti.com/lit/ds/symlink/sn65lvds1.pdf?ts=1672100269172&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FSN65LVDS1%252Fpart-details%252FSN65LVDS1D%253Futm_source%253Dgoogle%2526utm_medium%253Dcpc%2526utm_campaign%253Docb-tistore-promo-asc_opn_en-cpc-storeic-google-wwe%2526utm_content%253DDevice%2526ds_k%253DSN65LVDS1D%2526DCM%253Dyes%2526%2526utm_source%253Dgoogle%2526utm_medium%253Dcpc%2526utm_campaign%253D%2526utm_content%253D%2526ds_k%253Dsn65lvds1d%2526DCM%253Dyes%2526gclid%253DCjwKCAiAqaWdBhAvEiwAGAQltruYrSedpQ0uALxXlAq5xiuhmzbVhkdHlCKyi0L3cz9s1VCdN4uf8xoCVpwQAvD_BwE%2526gclsrc%253Daw.ds
 +  * https://hackaday.com/2020/05/11/new-teensy-4-1-arrives-with-100-mbps-ethernet-high-speed-usb-8-mb-flash/
 +  * https://twitter.com/PA4DAN/status/1108517564005695491/photo/1
 +  * https://www.fluxlight.com/content/Tech-Docs/AdTran%2012004800%20Datasheet.pdf
 +  * https://hackaday.com/2021/02/13/experiment-with-sfp-modules-with-this-handy-breakout/
    
 ===== References ===== ===== References =====
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 [(sparkfun_serialcomm>https://learn.sparkfun.com/tutorials/serial-communication)] [(sparkfun_serialcomm>https://learn.sparkfun.com/tutorials/serial-communication)]
 [(twi_protocol>https://ww1.microchip.com/downloads/en/devicedoc/doc0180.pdf)] [(twi_protocol>https://ww1.microchip.com/downloads/en/devicedoc/doc0180.pdf)]
 +
 +{{tag>electronics}}
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  • Last modified: 2022-12-21 07:01
  • by asdf