Tested with MPW9 Caravel.
Caravel has a lot of moving parts and can be confusing. Here's the way things are wired up.
- The cocotb test is wishbone_test/wishbone_test.py
- The C firmware is wishbone_test/wishbone_test.c
- The user project is wb_buttons_leds.v
Wiring:
- Buttons are connected on user GPIO 8 to 15
- LEDs are connected on user GPIO 16 to 23
- The firmware also writes to user GPIO 24 to 32 and toggles the single management GPIO
The C firmware sets up the GPIO, enables wishbone and then in a loop:
- reads the buttons via wishbone
- writes that value to the leds via wishbone
- mirrors that value to the GPIO
- toggles the management GPIO to sync with the cocotb testbench
The testbench waits for GPIO configuration to complete, and then:
- increments the value sent to buttons
- waits for sync by monitoring the management GPIO
- reads the LED output driven by the user project
- reads the GPIO output driven by C firmware
- asserts the LED, GPIO and button value are all the same
Clone this repository inside verilog/rtl/
Instantiate the module inside user_project_wrapper.v:
wb_buttons_leds wb_buttons_leds (
.wb_clk_i(wb_clk_i),
.wb_rst_i(wb_rst_i),
// MGMT SoC Wishbone Slave
.wbs_cyc_i(wbs_cyc_i),
.wbs_stb_i(wbs_stb_i),
.wbs_we_i (wbs_we_i ),
.wbs_adr_i(wbs_adr_i),
.wbs_dat_i(wbs_dat_i),
.wbs_ack_o(wbs_ack_o),
.wbs_dat_o(wbs_dat_o),
// IO Pads
.buttons (io_in [15:08]),
.leds (io_out[23:16]),
.oeb (io_oeb[23:08])
);
Include the RTL in the verilog/includes/includes.rtl.caravel_user_project file:
-v $(USER_PROJECT_VERILOG)/rtl/wishbone_buttons_leds/wb_buttons_leds.v
Copy the wishbone_test directory to verilog/dv/cocotb/
Add the test to verilog/dv/cocotb/cocotb_tests.py
from wishbone_test.wishbone_test import wishbone_test
Install caravel-cocotb: pip3 install caravel-cocotb
Run the test:
caravel_cocotb -test wishbone_test -tag wishbone_test
You should get a log message like this:
Check the trace:
gtkwave wishbone_test/wishbone_test.gtkw
It should look like this:
- gpio is going high and briefly low on each loop
- buttons are incrementing - driven by cocotb
- after a delay, leds match the button value
- 2 wishbone acks per loop (read buttons and write leds)
Requires Sby with SVA.
sby -f wb_buttons_leds.sby
To prove wishbone compliance.
- Caravel sim infrastructure: https://caravel-sim-infrastructure.readthedocs.io/
- Cocotb: https://www.cocotb.org/
- Management Core: https://caravel-mgmt-soc-litex.readthedocs.io/en/latest/
- Caravel: https://caravel-harness.readthedocs.io/en/latest/
Copyright Matt Venn 2023 and licensed under the GPL.