How to Change Configuration

When you want to change hardware configuration in the RVComp project, several generated files must stay in sync. RVComp provides two front ends for this task: make menuconfig for an interactive terminal UI and make cliconfig for scripted changes.

Configuration System Overview

Both front ends are implemented by RVComp/tools/setting.py. They do not generate a .config file or use Kconfig. Instead, they read the current settings from the repository and then update the relevant source files directly.

make menuconfig
    └─> uv run --project tools/ setting

make cliconfig ARGS="..."
    └─> uv run --project tools/ cliconfig ...

Updated files
    ├→ src/config.vh
    ├→ bootrom/rvcomp.dts
    ├→ bootrom/src/rvcomp_ether.h
    ├→ config.mk
    ├→ Makefile          # BAUD_RATE only
    └→ bootrom/src/bootloader.c

The last file is used to switch the bootrom between UART boot and MMC boot at compile time.

make menuconfig

$ make menuconfig

This target launches the curses-based configuration UI provided by tools/setting.py. The interface is menuconfig-style, but it is a standalone RVComp utility rather than the Linux Kconfig system.

Navigation:

Up / Down arrow: Move between items
Enter: Select or toggle the highlighted item
Left / Right arrow: Switch between the bottom buttons (Save, Load Default, Exit)

The top-level sections are:

Menu section	Parameters covered
Board	Target FPGA board (`nexys4ddr` / `arty_a7`)
Boot Method	UART boot or MMC boot (`nexys4ddr` only)
CPU / Branch Predictor	Clock frequency, PHT entries, BTB entries
Cache	L0/L1/L2 cache sizes
TLB	ITLB / DTLB entry counts
UART	Baud rate and FIFO depth
Ethernet	RX/TX buffer sizes

When you save the configuration, the tool writes the updated values back to the source files listed above.

After changing the configuration, regenerate the bitstream:

$ make reclockbit    # if you changed the clock frequency
$ make rebit         # for other configuration changes

make cliconfig

$ make cliconfig ARGS="--board arty_a7 --clk-freq 150"

This target runs the non-interactive CLI entry point in the same tool. It is intended for scripts and for cases where you already know the exact values you want to set.

usage: cliconfig [-h] [--board {nexys4ddr,arty_a7}] [--boot {mmc,uart}] [--default] [--clk-freq MHz] [--pht-entry N]
                 [--btb-entry N] [--l0-icache-size bytes] [--l1-icache-size bytes] [--l1-dcache-size bytes]
                 [--l2-cache-size bytes] [--itlb-entry N] [--dtlb-entry N] [--baudrate bps] [--fifo-depth N]

RVComp CLI configuration tool

Available boards: nexys4ddr, arty_a7

options:
  -h, --help            show this help message and exit
  --board {nexys4ddr,arty_a7}
                        FPGA board
  --boot {mmc,uart}     Boot method
  --default             Load board defaults (requires --board)
  --clk-freq MHz
  --pht-entry N
  --btb-entry N
  --l0-icache-size bytes
  --l1-icache-size bytes
  --l1-dcache-size bytes
  --l2-cache-size bytes
  --itlb-entry N
  --dtlb-entry N
  --baudrate bps
  --fifo-depth N

Examples:

# Change the target board to Arty A7 with MMC boot
$ make cliconfig ARGS="--board arty_a7"

# Change multiple settings at once
$ make cliconfig ARGS="--board nexys4ddr --clk-freq 160 --baudrate 3200000"

Updated Files

src/config.vh - Hardware Parameters

src/config.vh defines the RTL parameters used during synthesis, including board selection, cache sizes, TLB entry counts, UART settings, and Ethernet buffer sizes.

bootrom/rvcomp.dts - Device Tree

bootrom/rvcomp.dts is updated to keep the clock frequency, DRAM size, and peripheral address ranges consistent with the selected board and Ethernet buffer configuration.

bootrom/src/rvcomp_ether.h - Bare-Metal Ethernet Constants

bootrom/src/rvcomp_ether.h mirrors the Ethernet RX/TX buffer sizes for the bootrom-side software helpers.

config.mk / Makefile

config.mk is updated with board selection and BAUD_RATE. Makefile is also updated so the serial communication targets use the same UART baud rate.

bootrom/src/bootloader.c

The tool comments or uncomments #define UART_BOOT in bootloader.c so that the bootrom build matches the selected boot method.

Board Default Values

Parameter	Nexys 4 DDR	Arty A7
Clock Frequency	150 MHz	150 MHz
PHT Entries	8192	8192
BTB Entries	512	512
L0 ICache Size	1 KiB	1 KiB
L1 ICache Size	16 KiB	16 KiB
L1 DCache Size	16 KiB	16 KiB
L2 Cache Size	128 KiB	64 KiB
ITLB Entries	128	128
DTLB Entries	128	128
UART Baud Rate	3,000,000	3,000,000
UART FIFO Depth	2048	2048
Ethernet RX Buffer	16 KiB	16 KiB
Ethernet TX Buffer	8 KiB	4 KiB