FWPayload

FWPayload is a small processor+peripherals subsystem, targeting the user-project area of Caraval.

Block diagram

Current Status

FWPayload is taking Option #1 for integration into Caravel. Specifically, FWPayload is integrated into a customized version of user_proj_example (stored in verilog/rtl/fwpayload/user_proj_example.v). The config in openlane/user_proj_example creates a macro from this description, and that macro is integrated into user_project_wrapper using the provided configuration.

Openlane completes on user_proj_example with no DRC errors, and the following antenna violations:

Number of pins violated: 52
Number of nets violated: 51
Total number of nets: 34963

Running with diode-insertion strategy 3 (default) results in the following:

Number of pins violated: 193
Number of nets violated: 146
Total number of nets: 34963
[INFO]: Generating Final Summary Report...
[SUCCESS]: Flow Completed Without Fatal Errors.

Integration tests pass for both RTL and gate-level simulations.

On-boarding FWPayload

Caravel files (.gds,.lef,etc) have been copied from caravel/mpw-one-a tag on 20201206. A merged .gds is created by running the ‘ship’ target. The result is:

221398 problems occurred.  See feedback entries.
Using technology "sky130A", version 1.0.72-0-gb427e3b

Pre-Check Status

• Step 1 -- Pass
• Step 2 -- Pass
• Step 3 -- Fail
  • Documentation -- Pass
  • Makefile -- Pass
  • Pins -- Fail
    • Looks like the script finds arrayed ports in the .v and broken-out in the .lef
• Step 4 -- Fail

{{PROGRESS}} Executing Step 4 of 4: Checking DRC Violations.
{{PROGRESS}} Running DRC Checks...
{{FAIL}} DRC Checks on GDS-II Failed, Reason: Total # of DRC violations is 21405435
TEST FAILED AT STEP 4

External IP

FWPayload uses several pieces of external IP. Some are bundled with the project, and some are fetched during the project-initialization step.

FWRISC

RISC-V core originally targeted for FPGA application

• Git: https://github.com/mballance/fwrisc.git
• License: Apache 2.0

fw-wishbone-interconnect

Parameterized Wishbone interconnect

• Git: https://github.com/featherweight-ip/fw-wishbone-interconnect
• License: Apache 2.0

simple_spi_master

SPI master IP, obtained from the Caravel repository. Bundled with the project.

• License: GNU LGPL

simpleuart

UART IP, obtained from the Caravel repository. Bundled with the project.

• License: BSD-style

Memory map

The FWPayload memory map is designed to fit within the 28-bit user-area portion of the Caravel memory map.

• 0xX000_0000..0xX000_03FF - 1Kb register RAM
• 0xX100_0000..0xX100_00FF - UART
• 0xX100_0100..0xX100_01FF - SPI
• 0xX100_0200..0xX100_02FF - GPIO

Pin map

0 (i) - unused 1 (i) - unused 2 (i) - unused 3 (i) - unused 4 (i) - unused 5 (i) - unused 6 (i) - unused 7 (i) - unused 8 (i) - unused 9 (i) - unused 10 (i) - unused 11 (i) - unused 12 (o) - GPIO-out [0] 13 (o) - GPIO-out [1] 14 (o) - GPIO-out [2] 15 (o) - GPIO-out [3] 16 (o) - UART Tx 17 (i) - UART Rx 18 (i) - SPI SDI 19 (o) - SPI CSB 20 (o) - SPI SCK 21 (o) - SPI SDO 22 (o) - SPI SDOENB 23 (o) - GPIO-out [4] 24 (o) - GPIO-out [5] 25 (o) - GPIO-out [6] 26 (o) - GPIO-out [7] 27 (i) - GPIO-in [0] 28 (i) - GPIO-in [1] 29 (i) - GPIO-in [2] 30 (i) - GPIO-in [3] 31 (i) - GPIO-in [4] 32 (i) - GPIO-in [5] 33 (i) - GPIO-in [6] 34 (i) - GPIO-in [7] 35 (i) - unused 36 (i) - unused 37 (i) - unused

Bring-up/Debug Support

FWPayload uses the Caravel logic analyzer to configure reset and clocking, probe the program counter of the FWRISC, and optionally, single-step the clock.

• [127] - Controls the clock when configured as an output
• [126] - Controls the system reset (active low) when configured as an output
• [125] - Controls the FWRISC core reset when configured as an output
• [124:41] - unused
• [43:40] - Loopback, driving the GPIO input low bits
• [39:36] - Loopback, probing the GPIO output low bits
• [35] - unused
• [34] - Loopback, driving UART rx input
• [33] - Loopback, probing UART tx output
• [32] - Input, probing the ‘instruction-complete’ FWRISC net
• [31:0] - Input, probing the FWRISC program-counter net

Developer Notes

Required Tools

• Python 3 (3.6.8 was used)
• Icarus Verilog (11.0 was used)
• Verilator (4.102 was used)
• Openlane (rc5 from openlane/mpw-one-a tag was used)
• Skywater PDK (PDK_ROOT is assumed to be properly set)

Project Setup

The FWPayload project uses IVPM (IP and Verification Package Manager) to manage external IP and Python dependencies. The project can be setup both with and without IVPM installed.

In both cases, setting up the project will result in creation of a packages directory within the project that contains external IPs and required Python packages.

Setup with IVPM installed

Ensure IVPM is installed:

% pip3 install ivpm --user --upgrade

% cd <fwpayload_dir>
% ivpm update

Setup without IVPM installed

The project can also be setup without installing IVPM. The bootstrap.sh script is provided for this purpose. bootstrap.sh clones a local copy of ivpm.

% cd <fwpayload_dir>
% ./bootstrap.sh

Integration Testing

Testing of the fwpayload subsystem is done using a cocotb test environment. The block diagram is shown below:

Bus Functional Models (BFMs) are used to drive the Caravel management interface and logic-analyzer pins.

Tests

• fwrisc_gpio

  • Loads a small program into the RISC-V core that writes to the GPIO outputs
  • Drives the clock via the logic-analzer interface while monitoring the GPIO outputs

• mgmt_mem_access

  • Tests 1, 2, and 4-byte accesses to register RAM via the management interface

Running an individual test

Individual tests are run from the dv/ directory by running ‘make’.

% cd dv/fwrisc_gpio
% make clean
% make

Test Controls

Test behavior is controlled using environment variables.

• SIM - Selects the simulator to run
  • icarus -- Icarus Verilog (default)
  • vlsim -- Verilator, via the vlsim front-end
• DEBUG[=1] - Controls whether wave files should be saved