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PCIe Support on Tachyon

Tachyon comes with one PCIe connector, wired up for a PCIe 3.0 x1 (1-lane) interface. That means you’re getting up to 1 GB/s of theoretical peak bandwidth — enough to power NVMe SSDs, USB expansion hubs, and a variety of other PCIe goodies. No configuration needed — it’s enabled by default. Just plug and play!

Hardware Overview​

Tachyon is built around the Qualcomm QCM6490 chipset, which actually supports two lanes of PCIe 3.0 under the hood. But to keep things simple — and compatible with the Raspberry Pi PCIe ecosystem — we’re exposing just one lane via the PCIe connector.

There’s a dedicated 5V boost regulator powering the PCIe interface, and it shares that 5V line with the 40-pin header. Why a boost regulator? So that even if Tachyon is running on a 3.7V battery, your PCIe devices still get a clean 5V power supply. 💡

You can also turn PCIe power on or off in software, giving you more control and efficiency in battery-powered projects.

⚡ Power Tip: The maximum current draw is 2A, and that’s shared between the PCIe port and the 5V pin on the 40-pin header. So if you’re using both a HAT and a PCIe peripheral, double-check their combined draw — make sure it stays well below that 2A limit!

PCIe Connector Pinout​

Tachyon PCIe pinout

Hardware Setup​

Connecting PCIe devices​

  • Gently lift the retention clip
  • Insert the FPC cable with the pin contacts facing away from the clip
  • Gently re-insert the retention clip, firmly seating the cable into the connector

⚠️ Caution: Verify the cable orientation of your PCIe device before powering on your tachyon! Incorrectly oriented cables could damage your Tachyon or PCIe device.

Pin 1 is the 5v power pin, and is the side closest to the USBC connectors

Pimoroni power LED on

Supported HATs​

NVMe drives and USB hubs generally work without any additional drivers. Some specific boards that have been tested are:

NVME Drive Setup With Pimoroni NVMe Base​

Tachyon and Pimoroni NVMe base

Hardware Setup​

  • Insert the NVMe drive into the base
  • Connect the base to the Tachyon, making sure the cable pin contacts face away from the retention clip
FPC Cable orientation
  • Power on the Tachyon, the NVMe base Power LED should come on shortly after Tachyon is powered on
Pimoroni power LED on

Software setup​

  • Examine PCIe devices with lspci

    lspci
    0000:00:00.0 PCI bridge: Qualcomm Device 010b
    0000:01:00.0 Network controller: Qualcomm Device 1103 (rev 01)
    0001:00:00.0 PCI bridge: Qualcomm Device 010b
    0001:01:00.0 PCI bridge: ASMedia Technology Inc. Device 1182
    0001:02:03.0 PCI bridge: ASMedia Technology Inc. Device 1182
    0001:02:07.0 PCI bridge: ASMedia Technology Inc. Device 1182
    0001:04:00.0 Non-Volatile memory controller: Phison Electronics Corporation Device 5021 (rev 01)

    PCI bridge 0 is the internal connection to the WiFi/Bluetooth SoC. PCI bridge 1 is the external PCIe connector. Here we can see the NVME controller has been detected.

  • We can see a block device has been created at /dev/nvme0n1. We can examine it with lsblk

    lsblk | grep nvme0n1
    nvme0n1 259:35   0 953.9G  0 disk

  • We can format the drive with fdisk. Generally the options are n for new partition, p for primary partition, defaults for sector start and end, and finally w to write and quit.

    sudo fdisk /dev/nvme0n1
    [sudo] password for particle:

    Welcome to fdisk (util-linux 2.34).
    Changes will remain in memory only, until you decide to write them.
    Be careful before using the write command.

    Device does not contain a recognized partition table.
    Created a new DOS disklabel with disk identifier 0x06a8f583.

    Command (m for help): n
    Partition type
       p   primary (0 primary, 0 extended, 4 free)
       e   extended (container for logical partitions)
    Select (default p): p
    Partition number (1-4, default 1): 1
    First sector (2048-2000409263, default 2048): 2048
    Last sector, +/-sectors or +/-size{K,M,G,T,P} (2048-2000409263, default 2000409263): 2000409263

    Created a new partition 1 of type 'Linux' and of size 953.9 GiB.

    Command (m for help): w
    The partition table has been altered.
    Calling ioctl() to re-read partition table.
    Syncing disks.

  • Format the new partition, this may take some time depending on the size of your disk

    sudo mkfs.ext4 /dev/nvme0n1
    mke2fs 1.45.7 (28-Jan-2021)
    Found a dos partition table in /dev/nvme0n1
    Proceed anyway? (y,N) y
    Discarding device blocks: done
    Creating filesystem with 250051158 4k blocks and 62513152 inodes
    Filesystem UUID: 5520786a-782e-4715-9165-3334f4f0f931
    Superblock backups stored on blocks:
    	32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
    	4096000, 7962624, 11239424, 20480000, 23887872, 71663616, 78675968,
    	102400000, 214990848

    Allocating group tables: done
    Writing inode tables: done
    Creating journal (262144 blocks):

    done
    Writing superblocks and filesystem accounting information: done

  • Mount the new partition

    sudo mount /dev/nvme0n1 /mnt/

    The NVMe drive is now available for use

    lsblk | grep nvme0n1
    nvme0n1 259:35   0 953.9G  0 disk /mnt

Troubleshooting​

Forcing Bus Re-enumeration​

To force scanning of the PCIe root complex in order to detect new devices

echo 1 > /sys/bus/pci/rescan

Drive Write Testing​

Drive write speed can be tested with the dd utility

sudo dd if=/dev/zero of=/mnt/test.bin bs=4k iflag=fullblock,count_bytes count=1G
262144+0 records in
262144+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 4.60684 s, 233 MB/s