Caravel Architecture

Caravel is composed of the harness frame plus two wrappers for drop-in modules for the management area and user project area.

Harness Definition

The harness itself contains the clocking module, DLL, user ID, housekeeping SPI, POR, and GPIO control.

GPIO handling moved out of management SoC and into SPI. SPI gets a wishbone interface; the management SoC talks to the SPI through wishbone, not by taking over the 4-pin SPI interface.

A new block like the ID has the mode at power-up for each GPIO. Can be configured with a text file. SPI pins are fixed for operation on startup.

On power-up, the SPI automatically configures the GPIO. Manual load is possible from both the SPI and from the wishbone bus.

All functions within the harness but outside the management SoC are incorporated into one large module called “housekeeping”. This includes a number of registers for all the included functions, with a “front door” SPI interface connected to the padframe through GPIO pins 1 to 4, and a “back door” wishbone interface connected to the management SoC. The management Soc reserves the memory block at 0x26000000 for the housekeeping module. The housekeeping module exchanges data with the management SoC via an interface that uses the byte- wide SPI register data. A small state machine reads four contiguous wishbone addresses and an address decoder determines the corresponding SPI register. The state machine stalls the SoC until all four bytes have been handled before returning the acknowledge signal.

Management Area

The management area is a drop-in module implemented as a separate repo. It typically includes a RISC-V based SoC that includes a number of peripherals like timers, uart, and gpio. The management area runs firmware that can be used to:

  • Configure User Project I/O pads

  • Observe and control User Project signals (through on-chip logic analyzer probes)

  • Control the User Project power supply

The management area implements SRAM for the management SoC.

The default instantiation for the management core can be found here . See documentation of the management core for further details.

User Project Area

This is the user space. It has a limited silicon area 2.92mm x 3.52mm as well as a fixed number of I/O pads 38 and power pads 4.

The user space has access to the following utilities provided by the management SoC:

  • 38 IO Ports

  • 128 Logic analyzer probes

  • Wishbone port connection to the management SoC wishbone bus.

Quick Start for User Projects

Your area is the full user space, so feel free to add your project there or create a different macro and harden it separately then insert it into the user_project_wrapper for digital projects or insert it into user_project_analog_wrapper for analog projects.

Digital User Project

If you are building a digital project for the user space, check a sample project at caravel_user_project.

If you will use OpenLANE to harden your design, go through the instructions in this README.

Digital user projects should adhere the following requirements: