Forcing PCI Express Gen 3.0 speeds on the Pi 5 #PiDay #RaspberryPi @geerlingguy @Raspberry_Pi
Jeff Geerling has been exploring the PCIe bus on the new Raspberry Pi 5 and has documented some interesting things, some rather unexpected like the ability to change the speed of the PCIe bus.
In my recent Adafruit Blog article PCIe Bandwidth, I discuss the generations the specification has gone through and with each one comes an increase in bus speed. Gen 1.0 was the original and defined a 2.5 gigatransfers per second (GT/s) speed. Gen 2.0 defined 5 GT/s and 3.0 8 GT/s on a single lane (which scales up linearly per number of lanes). The bus is backwards compatible, re. a Gen 1.0 device can work in a Gen 2.0 slot. But a Gen 3.0 device may or may not like that it is in a Gen 2.0 slot, depending on it’s function and driver.
There are 5 active PCIe lanes on the Raspberry Pi 5 with four going to the RP1 chip and one is broken out to the new PCIe connector. Jeff states:
By default, all PCIe lanes operate at Gen 2.0 speeds, or about 5 GT/sec per lane. Currently there’s no way to change that default for the RP1 chip’s ‘internal’ lanes, but on the external connector, you can add the following lines inside /boot/config.txt (and reboot) to upgrade the connection to Gen 3.0 (8 GT/sec, almost double the speed):
dtparam=pciex1
dtparam=pciex1_gen=3
And yes, you can also downgrade the connection to Gen 1.0 speeds (2.5 GT/sec) if you like.
Why default to PCIe Gen 2.0?
Why is it defaulted to Gen 2.0? Because that’s the speed at which the board could be certified for PCI Express. Even older standards like 2.0 and 3.0 are considered ‘high speed’ interconnects. And with any connection on a board, interference and signal issues can cause problems with higher bandwidth.
Adafruit publishes a wide range of writing and video content, including interviews and reporting on the maker market and the wider technology world. Our standards page is intended as a guide to best practices that Adafruit uses, as well as an outline of the ethical standards Adafruit aspires to. While Adafruit is not an independent journalistic institution, Adafruit strives to be a fair, informative, and positive voice within the community – check it out here: adafruit.com/editorialstandards
Stop breadboarding and soldering – start making immediately! Adafruit’s Circuit Playground is jam-packed with LEDs, sensors, buttons, alligator clip pads and more. Build projects with Circuit Playground in a few minutes with the drag-and-drop MakeCode programming site, learn computer science using the CS Discoveries class on code.org, jump into CircuitPython to learn Python and hardware together, TinyGO, or even use the Arduino IDE. Circuit Playground Express is the newest and best Circuit Playground board, with support for CircuitPython, MakeCode, and Arduino. It has a powerful processor, 10 NeoPixels, mini speaker, InfraRed receive and transmit, two buttons, a switch, 14 alligator clip pads, and lots of sensors: capacitive touch, IR proximity, temperature, light, motion and sound. A whole wide world of electronics and coding is waiting for you, and it fits in the palm of your hand.
Have an amazing project to share? The Electronics Show and Tell is every Wednesday at 7:30pm ET! To join, head over to YouTube and check out the show’s live chat and our Discord!
Python for Microcontrollers – Adafruit Daily — Python on Microcontrollers Newsletter: Open Hardware is In, New CircuitPython and Pi 5 16GB, and much more! #CircuitPython #Python #micropython @ThePSF @Raspberry_Pi
EYE on NPI – Adafruit Daily — EYE on NPI Maxim’s Himalaya uSLIC Step-Down Power Module #EyeOnNPI @maximintegrated @digikey
