7 ms·

Raspberry Pi Compute Module 5 Is in Development

36 points by WithinReason 3y ago

rocky1138 3y ago
Very happy to read that it uses the same form factor and connections as CM4 did. I was hoping we wouldn't even up with yet another socket.
- jacquesm 3y ago
  I'd love to use these but the connectors are what has been putting me off. This is beyond my skill level.
  - dragontamer 3y ago
    I've never done it myself, but isn't the stacking connector just as easy as grabbing DF40HC(3.0)-100DS-0.4v (https://www.digikey.com/en/products/detail/hirose-electric-co-ltd/DF40HC(3.0)-100DS-0.4V(58)/5155905 https://www.digikey.com/en/products/detail/hirose-electric-c...), throwing it into a KiCAD 2-layer or 4-layer board (depending on how complex you want to make it), and then just... that's it? There's no RAM or other complex signals at play here. I have to imagine that 2-layer boards are sufficient for the vast majority of CM4 board users. I guess a few elements in the connector (USB and Ethernet) are differential pairs. So okay, you need to know a bit about transmission line theory. But as far as actually running differential pairs with matched-impedances, its just a matter of knowing what a "dielectric constant" is and plugging that into the calculator, so that you know how thick the PCB-trace should be in a stripline. Which is all nearly automatic even with free tools like KiCAD today. Okay, you need to know what the word "dielectric constant" is and that striplines are an impedance-controlled design pattern wherein the width of the PCB-trace on top is matched to a ground-plane below... and that you need the words "Dielectric Constant" and and "Board Thickness" to calculate the width for the impedance you're looking for. But bam, now you know everything for simpler signals like USB or Ethernet. But honestly, whatever PCB you're designing is probably so small that it'd still work without needing to know any of this deeper theory.
    - foofie 3y ago
      > I guess a few elements in the connector (USB and Ethernet) are differential pairs. So okay, you need to know a bit about transmission line theory. But as far as actually running differential pairs with matched-impedances, its just a matter of knowing what a "dielectric constant" is and plugging that into the calculator, so that you know how thick the PCB-trace should be in a stripline. You understand that none of this is doable by anyone without a background in EE, don't you?
      - dragontamer 3y ago
        You understand that everything I said was... Plug in the right values here: https://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-pcb-trace-impedance https://www.digikey.com/en/resources/conversion-calculators/... You don't need an EE degree to look at your PCB-manufacturer's specifications. Lets run a brief example: https://www.digikey.com/-/media/Images/Marketing/Resources/DKRed/DKRed%20-%204%20Layer%20Stack%20Info.pdf?la=en-US&ts=8f209b2c-515f-495d-a3da-806b275c331d https://www.digikey.com/-/media/Images/Marketing/Resources/D... Lets go for Edge Coupled Microstrip. Solve for Trace Width. I believe Ethernet is 100 Ohms differential impedance. Set the top to 100. Trace Thickness as per DKRed is 0.5 oz/ft^2. This value might be 1 on different manufacturers. Height is 7.04 mil. Just steal it from the specsheet above. Spacing is whatever you plan to do. Lets say 8-mil. Dielectric Constant is 4.01: https://www.digikey.com/-/media/Images/Marketing/Resources/DKRed/185hr%20Datasheet.pdf?la=en-US&ts=fdcadd73-9742-4bb2-b3d8-e693d8bddd48 https://www.digikey.com/-/media/Images/Marketing/Resources/D.... See "Dk", Dielectric Constant. ------------------ Bam. Now 9.814 mil thickness for differential pair Ethernet routes. Yeah, it will take you some study. But I literally laid everything out in front of you with my post above. It shouldn't take you any more than like 30 minutes of studying at this point now that I put everything in just a few posts for you. An EE Degree will help. But... there's not much to this particular issue. You need to understand that different manufacturers have different thicknesses, dielectric-constants and other such measurements. But its all plug-and-play once you know how to read a spec-sheet. -------- If that's too hard, just don't route Ethernet or USB I guess? There aren't very many differential-pair lines or impedance-matched lines on the Rasp. Pi4 CM as far as I can tell.
supportengineer 3y ago
On a side note, when did this term "compute" work its way into the lexicon? "Compute nodes", etc. I don't recall this being a term until the last year or so.
- jacquesm 3y ago
  With Plan 9 or so in the previous century?
- dragontamer 3y ago
  Most supercomputer clusters are divided into compute-nodes vs management nodes. I'd have to imagine the language was popular as far back as the 1980s in the high-performance computing realm...
  - marcosdumay 3y ago
    There are also IO nodes, that talk to disks and network. Mainframes use those names too. I'm not sure what name blade hacks use (yeah, I'm out of a datacenter for that long), but they have those things too.
  - semi-extrinsic 3y ago
    Supercomputers were not clusters like we have today until the mid-90's. In the first written description of how to build a Beowulf cluster, by Radajewski and Eadline in 1998 [1], the management node was refered to as the "server node" and the compute nodes as "client nodes". I believe the term "compute node" was first used in the context of the Intel ASCI Red supercomputer that was installed at Sandia in 1997. This later led to the Cray XT3, XT4, XT5 families of machines that used the same terminology. But I believe the term was not in generic usage outside of those specific supercomputers until around 2005-2010. [1] https://ibiblio.org/pub/Linux/docs/HOWTO/archive/Beowulf-HOWTO.html#ss2.2 https://ibiblio.org/pub/Linux/docs/HOWTO/archive/Beowulf-HOW...
- wharvle 3y ago
  I don't recall ever seeing or hearing "compute" used as anything but a verb until several years into the rise of the "cloud".
not_your_vase 3y ago
Compute Module on a platform that recommends active cooling? Excellent. Simply excellent.
- postpawl 3y ago
  Home Assistant yellow seems to have a pretty good solution, but it’s not currently active cooling for cm4. It’s a lot like a cpu cooler mount. Can see pictures here: https://www.jeffgeerling.com/blog/2022/home-assistant-yellow-pi-powered-local-automation https://www.jeffgeerling.com/blog/2022/home-assistant-yellow...
VikingCoder 3y ago
I want the 500...

36 points by WithinReason 3y ago

Very happy to read that it uses the same form factor and connections as CM4 did. I was hoping we wouldn't even up with yet another socket.

jacquesm 3y ago
I'd love to use these but the connectors are what has been putting me off. This is beyond my skill level.
- dragontamer 3y ago
  I've never done it myself, but isn't the stacking connector just as easy as grabbing DF40HC(3.0)-100DS-0.4v (https://www.digikey.com/en/products/detail/hirose-electric-co-ltd/DF40HC(3.0)-100DS-0.4V(58)/5155905 https://www.digikey.com/en/products/detail/hirose-electric-c...), throwing it into a KiCAD 2-layer or 4-layer board (depending on how complex you want to make it), and then just... that's it? There's no RAM or other complex signals at play here. I have to imagine that 2-layer boards are sufficient for the vast majority of CM4 board users. I guess a few elements in the connector (USB and Ethernet) are differential pairs. So okay, you need to know a bit about transmission line theory. But as far as actually running differential pairs with matched-impedances, its just a matter of knowing what a "dielectric constant" is and plugging that into the calculator, so that you know how thick the PCB-trace should be in a stripline. Which is all nearly automatic even with free tools like KiCAD today. Okay, you need to know what the word "dielectric constant" is and that striplines are an impedance-controlled design pattern wherein the width of the PCB-trace on top is matched to a ground-plane below... and that you need the words "Dielectric Constant" and and "Board Thickness" to calculate the width for the impedance you're looking for. But bam, now you know everything for simpler signals like USB or Ethernet. But honestly, whatever PCB you're designing is probably so small that it'd still work without needing to know any of this deeper theory.
  - foofie 3y ago
    > I guess a few elements in the connector (USB and Ethernet) are differential pairs. So okay, you need to know a bit about transmission line theory. But as far as actually running differential pairs with matched-impedances, its just a matter of knowing what a "dielectric constant" is and plugging that into the calculator, so that you know how thick the PCB-trace should be in a stripline. You understand that none of this is doable by anyone without a background in EE, don't you?
    - dragontamer 3y ago
      You understand that everything I said was... Plug in the right values here: https://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-pcb-trace-impedance https://www.digikey.com/en/resources/conversion-calculators/... You don't need an EE degree to look at your PCB-manufacturer's specifications. Lets run a brief example: https://www.digikey.com/-/media/Images/Marketing/Resources/DKRed/DKRed%20-%204%20Layer%20Stack%20Info.pdf?la=en-US&ts=8f209b2c-515f-495d-a3da-806b275c331d https://www.digikey.com/-/media/Images/Marketing/Resources/D... Lets go for Edge Coupled Microstrip. Solve for Trace Width. I believe Ethernet is 100 Ohms differential impedance. Set the top to 100. Trace Thickness as per DKRed is 0.5 oz/ft^2. This value might be 1 on different manufacturers. Height is 7.04 mil. Just steal it from the specsheet above. Spacing is whatever you plan to do. Lets say 8-mil. Dielectric Constant is 4.01: https://www.digikey.com/-/media/Images/Marketing/Resources/DKRed/185hr%20Datasheet.pdf?la=en-US&ts=fdcadd73-9742-4bb2-b3d8-e693d8bddd48 https://www.digikey.com/-/media/Images/Marketing/Resources/D.... See "Dk", Dielectric Constant. ------------------ Bam. Now 9.814 mil thickness for differential pair Ethernet routes. Yeah, it will take you some study. But I literally laid everything out in front of you with my post above. It shouldn't take you any more than like 30 minutes of studying at this point now that I put everything in just a few posts for you. An EE Degree will help. But... there's not much to this particular issue. You need to understand that different manufacturers have different thicknesses, dielectric-constants and other such measurements. But its all plug-and-play once you know how to read a spec-sheet. -------- If that's too hard, just don't route Ethernet or USB I guess? There aren't very many differential-pair lines or impedance-matched lines on the Rasp. Pi4 CM as far as I can tell.

supportengineer 3y ago

On a side note, when did this term "compute" work its way into the lexicon? "Compute nodes", etc. I don't recall this being a term until the last year or so.

jacquesm 3y ago
With Plan 9 or so in the previous century?
dragontamer 3y ago
Most supercomputer clusters are divided into compute-nodes vs management nodes. I'd have to imagine the language was popular as far back as the 1980s in the high-performance computing realm...
- marcosdumay 3y ago
  There are also IO nodes, that talk to disks and network. Mainframes use those names too. I'm not sure what name blade hacks use (yeah, I'm out of a datacenter for that long), but they have those things too.
- semi-extrinsic 3y ago
  Supercomputers were not clusters like we have today until the mid-90's. In the first written description of how to build a Beowulf cluster, by Radajewski and Eadline in 1998 [1], the management node was refered to as the "server node" and the compute nodes as "client nodes". I believe the term "compute node" was first used in the context of the Intel ASCI Red supercomputer that was installed at Sandia in 1997. This later led to the Cray XT3, XT4, XT5 families of machines that used the same terminology. But I believe the term was not in generic usage outside of those specific supercomputers until around 2005-2010. [1] https://ibiblio.org/pub/Linux/docs/HOWTO/archive/Beowulf-HOWTO.html#ss2.2 https://ibiblio.org/pub/Linux/docs/HOWTO/archive/Beowulf-HOW...
wharvle 3y ago
I don't recall ever seeing or hearing "compute" used as anything but a verb until several years into the rise of the "cloud".

not_your_vase 3y ago

Compute Module on a platform that recommends active cooling? Excellent. Simply excellent.

postpawl 3y ago
Home Assistant yellow seems to have a pretty good solution, but it’s not currently active cooling for cm4. It’s a lot like a cpu cooler mount. Can see pictures here: https://www.jeffgeerling.com/blog/2022/home-assistant-yellow-pi-powered-local-automation https://www.jeffgeerling.com/blog/2022/home-assistant-yellow...

VikingCoder 3y ago

I want the 500...