OpenTitan Earl Grey
Overview
The OpenTitan Earl Grey chip is a low-power secure microcontroller that is designed for several use cases requiring hardware security. The OpenTitan Github [2] page contains HDL code, utilities, and documentation relevant to the chip.
Hardware
RV32IMCB RISC-V “Ibex” core
128kB main SRAM
Fixed-frequency and AON timers
32 x GPIO
4 x UART
3 x I2C
2 x SPI host
1 x SPI device
Various security peripherals
Detailed specification is on the OpenTitan Earl Grey Chip Datasheet [1].
Supported Features
The opentitan_earlgrey board configuration is designed and tested to run on
the Earl Grey chip simulated in Verilator, a cycle-accurate HDL simulation tool.
Interface |
Controller |
Driver/Component |
|---|---|---|
NVIC |
on-chip |
nested vector interrupt controller |
Timer |
on-chip |
RISC-V Machine Timer |
UART |
on-chip |
serial port-polling |
SPI |
on-chip |
SPI host |
WDT |
on-chip |
Always-On Timer (Watchdog) |
Other hardware features are not yet supported on Zephyr porting.
Programming and Debugging
First, build and install Verilator as described in the OpenTitan Verilator Setup [3] guide .
Building and Flashing
Here is an example for building the Hello World application. The following steps were tested on OpenTitan master branch @ 6a3c2e98.
# From the root of the zephyr repository
west build -b opentitan_earlgrey samples/hello_world
The OpenTitan Vchip_sim_tb tool can take the Zephyr .elf as input and place it in simulated flash. The OpenTitan test ROM will then run in simulation, read the manifest header from simulated flash, and begin executing Zephyr from the entry point.
$OT_HOME/bazel-bin/hw/build.verilator_real/sim-verilator/Vchip_sim_tb --verbose-mem-load \
-r $OT_HOME/bazel-out/k8-fastbuild-ST-2cc462681f62/bin/sw/device/lib/testing/test_rom/test_rom_sim_verilator.39.scr.vmem \
--meminit=otp,$OT_HOME/bazel-out/k8-fastbuild/bin/hw/ip/otp_ctrl/data/img_rma.24.vmem \
--meminit=flash,$ZEPHYR_PATH/build/zephyr/zephyr.elf
UART output:
I00000 test_rom.c:135] Version: earlgrey_silver_release_v5-9599-g6a3c2e988, Build Date: 2023-01-17 16:02:09
I00001 test_rom.c:237] Test ROM complete, jumping to flash (addr: 20000384)!
*** Booting Zephyr OS build zephyr-v3.2.0-3494-gf0729b494b98 ***
Hello World! opentitan_earlgrey