4 ms·

New Raspberry Pi: Compute Module 4S

26 points by TimLeland 5y ago

lloydatkinson 5y ago
Frustrating they keep releasing new models but no new model A
- deleted 5y ago
  [deleted]
avian 5y ago
Frustrating that they keep releasing new models when even existing models continue to be unobtainable through normal supply channels. That said, I can understand why they went back to the old form factor. The new high-density connectors required for CM4 integration are a single-source item, don't have any alternatives [1], and are out of stock everywhere [2]. On the other hand, the older SO-DIMM connectors are a commodity item that can be sourced from a number of manufacturers. The SO-DIMM connectors are also much more convenient and robust for removing and re-attaching the CM. Raspberry Pi makes it relatively hard to flash the eMMC on the CM in-system if you include any USB periphery on-board. Because of this a production process will generally include the CM being placed at least once onto a dedicated flashing board before being placed onto the final device. [1] https://forums.raspberrypi.com/viewtopic.php?t=325885&sid=711e983eff15d233f2f18e1ba2168788 https://forums.raspberrypi.com/viewtopic.php?t=325885&sid=71... [2] https://octopart.com/search?q=DF40C-100DS-0.4V%2851%29&currency=USD&specs=0 https://octopart.com/search?q=DF40C-100DS-0.4V%2851%29&curre...
- joezydeco 5y ago
  The design with those dual mezzanine connectors was bad to begin with. So much so that Hirose put out a design document saying "please don't do this because the tolerance stackup is impossible". https://www.hirose.com/ja/product/document?clcode=CL0684-4042-5-51&productname=DF40C(2.0)-40DS-0.4V(51)&series=DF40&documenttype=Guideline&lang=ja&documentid=0001442210 https://www.hirose.com/ja/product/document?clcode=CL0684-404...
  - avian 5y ago
    Interesting. I was not aware of this document. Thanks for the link! The recommendation against using multiple connectors on a single board seems to be largely ignored in the wild though. I've seen similar products that use two or even three DF40-series connectors on the same PCB. Here's one example from the top of my head: https://www.variscite.com/product/system-on-module-som/cortex-a53-krait/dart-mx8m-plus-nxp-i-mx-8m-plus/ https://www.variscite.com/product/system-on-module-som/corte...
    - joezydeco 5y ago
      Yeah, TechNexion does it as well. I'm not sure why the CM4 had trouble but maybe with enough force it fits once and everyone just looks the other way. Or perhaps the trouble is with other people trying to design compatible boards and just not getting the placement exactly right compared to how the RPi board house has it set up.

26 points by TimLeland 5y ago

lloydatkinson 5y ago

Frustrating they keep releasing new models but no new model A

deleted 5y ago
[deleted]

avian 5y ago

Frustrating that they keep releasing new models when even existing models continue to be unobtainable through normal supply channels. That said, I can understand why they went back to the old form factor. The new high-density connectors required for CM4 integration are a single-source item, don't have any alternatives [1], and are out of stock everywhere [2]. On the other hand, the older SO-DIMM connectors are a commodity item that can be sourced from a number of manufacturers. The SO-DIMM connectors are also much more convenient and robust for removing and re-attaching the CM. Raspberry Pi makes it relatively hard to flash the eMMC on the CM in-system if you include any USB periphery on-board. Because of this a production process will generally include the CM being placed at least once onto a dedicated flashing board before being placed onto the final device. [1] https://forums.raspberrypi.com/viewtopic.php?t=325885&sid=711e983eff15d233f2f18e1ba2168788 https://forums.raspberrypi.com/viewtopic.php?t=325885&sid=71... [2] https://octopart.com/search?q=DF40C-100DS-0.4V%2851%29&currency=USD&specs=0 https://octopart.com/search?q=DF40C-100DS-0.4V%2851%29&curre...

joezydeco 5y ago
The design with those dual mezzanine connectors was bad to begin with. So much so that Hirose put out a design document saying "please don't do this because the tolerance stackup is impossible". https://www.hirose.com/ja/product/document?clcode=CL0684-4042-5-51&productname=DF40C(2.0)-40DS-0.4V(51)&series=DF40&documenttype=Guideline&lang=ja&documentid=0001442210 https://www.hirose.com/ja/product/document?clcode=CL0684-404...
- avian 5y ago
  Interesting. I was not aware of this document. Thanks for the link! The recommendation against using multiple connectors on a single board seems to be largely ignored in the wild though. I've seen similar products that use two or even three DF40-series connectors on the same PCB. Here's one example from the top of my head: https://www.variscite.com/product/system-on-module-som/cortex-a53-krait/dart-mx8m-plus-nxp-i-mx-8m-plus/ https://www.variscite.com/product/system-on-module-som/corte...
  - joezydeco 5y ago
    Yeah, TechNexion does it as well. I'm not sure why the CM4 had trouble but maybe with enough force it fits once and everyone just looks the other way. Or perhaps the trouble is with other people trying to design compatible boards and just not getting the placement exactly right compared to how the RPi board house has it set up.