Feature #5417


S/T (S0) ISDN BRI adapter with VCXO / GPS-DO

Added by laforge 7 months ago. Updated about 2 months ago.

In Progress
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So.. As part of the Community_TDMSS7_Network, offering PRI is nice but most people will have BRI equipment (modems, ISDN-TA, small home PBX, ...) that they'd be interested in attaching.

Doing this with COTS ISDN adapters is not an option, as we cannot control their clock to match the master clock of the TDMoIP network.

I've been brainstorming a potential design and validated component availability. Currently I'm thinking of something like this

  • CologneChip XHFC-2SU (2-port S0) controller IC, operated in NT mode
    • available from stock at MOQ-160 from CologneChip
  • Matching dual magnetics.
    • digikey + mouser have a few pulse parts still in stock (low qty): T5007
    • Sumida has stopped all production
    • Talema has 30 weeks lead time
    • UMEC still has some stock of UT20795-5MTS, I'm putting a 250 unit reel on sysmocom stock right now
  • clocking
    • 10 MHz VCXO (optional external 10 MHz input in case somebody already has GPS-DO around)
    • some clock divider to bring this down to 8kHz. If we have no other programmable logic or timer/counter blocks that can be used, an ATTiny clocked off 10MHz (no prescaler, counter generating interrupt every 250 cycles, divide-by-5 in software/irq-handler) approach can be used - doen in a lot of DYI 10MHz -> 1PPS designs.
    • some PWM or DAC to drive the VXCO

The more interesting question is the interface on the "Compute" side.

Possible high-level approaches:
  1. USB-attached to some Linux PC
    • more analoguous to icE1usb, but requires an additonal computer
  2. Raspi hat (or beagle or the like)
    • I'm not a big raspi fan, but they are very popular
  3. built-in Ethernet for direct TDMoIP
    • most easy to deploy, would allow people without Linux knowledge to simply plug+play

Right now I'm leaning mostly towards something self-contained with built-in Ethernet.

The major problem right now is availability of uC or FPGA.
  • STM32 are basically vanished off the planet
  • iCE40 equally not available (yes, tnt might get 100, but ...)

One thought might be to use an SAME5x (sysmocom uses that part in the sysmoOCTSIM and has some stock. It is a bit on the high-end side compared to the requirements).


xhfc-2su.pdf View xhfc-2su.pdf 6.02 MB XHFC-2SU laforge, 02/06/2022 08:58 AM
xhfc2su-line.png View xhfc2su-line.png 73.1 KB laforge, 04/07/2022 05:50 PM
xhfc2su-breakout-v1.jpg View xhfc2su-breakout-v1.jpg 1.6 MB laforge, 05/19/2022 08:15 PM
krcjdhxylma.jpg View krcjdhxylma.jpg 2.94 MB manawyrm, 05/25/2022 10:38 PM
sbwvaixyeok.png View sbwvaixyeok.png 25.8 KB manawyrm, 05/25/2022 10:38 PM
gwjbeqsytvk.png View gwjbeqsytvk.png 1.5 KB manawyrm, 05/25/2022 10:38 PM
nxodmpghkas.jpg View nxodmpghkas.jpg 2.85 MB manawyrm, 05/25/2022 10:44 PM
wltvrxeaych.jpg View wltvrxeaych.jpg 3.57 MB manawyrm, 05/28/2022 09:48 PM
misdn_xhfc2su.patch misdn_xhfc2su.patch 189 KB manawyrm, 06/16/2022 01:37 PM


  • sourcing of magnetics
  • design XHFC-2SU board to connect to ATSAMV1-XULT
  • sourcing of XHFC-2SU
  • sourcing of ATSAMV71
  • sourcing of VCXO
  • testing of xhfc2su-breakout v1

Related issues

Related to OCTOI - Osmocom Community TDM over IP - Feature #5436: BRI variant of OCTOI protocolNewlaforge01/30/2022


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