iCE40 E1 USB interface¶

This page is the main entry point for the E1 Software defined interface using the iCE40 FPGA as the core.

Architecture¶

This approach tries to implement as much as possible inside an iCE40 FPGA

Particularly, the iCE40 FPGA

• contains the E1 PHY. There is no external LIU*, reducing the BOM cost significantly. Instead, the comparators of the FPGA are used. In practice, this has shown to work on short E1 links of a few meters. We'd expect some problems in terms of long-haul E1 links, but those are not really the target use case here.
• contains the E1 framer, including frame alignment
• contains a USB softcore (no external USB PHY needed)
• contains a PicoRISCV softcore to implement USB protocol handling and to connect the E1 softcore with the USB softcore

So all-in-all, we can build a USB-E1 interface from little more than an iCE40 FPGA and an E1 line transformer!

Current stack¶

• The hardware is currently not documented, only few prototypes exists and have been half hand-wired. They are currently based off iCEBreaker and iCEBreaker-bitsy iCE40 dev boards. ( https://github.com/icebreaker-fpga/icebreaker ) as well as iCEpick by tnt.
• The gateware is temporarily hosted in the 'e1' branch of this repo : https://github.com/smunaut/ice40-playground/tree/e1/projects/riscv_usb
• The embedded software is in the same repository as above, in the 'fw' sub-directory : https://github.com/smunaut/ice40-playground/tree/e1/projects/riscv_usb/fw
• The userspace daemon that handles the USB communication is hosted at: https://git.osmocom.org/osmo-e1d
• The support for this daemon interface to the rest of the cellular stack is in a 'tnt/e1d' branch of the libosmo-abis repo : https://git.osmocom.org/libosmo-abis/log/?h=tnt/e1d

Presentations¶

• Talk from OsmoCon 2018 about the Software Defined E1 project as a whole : osmocon_2018_e1.pdf
• Talk from OsmoDevCon 2019 about the iCE40 based solution specifically: osmodevcon_2019_e1.pdf

video recording of the iC40 based approach / OsmoDevCoon 2019