GitHub - GrieferPig/esp32-s31-linux: Porting MMU Linux to ESP32-S31

Linux 6.12 for ESP32-S31 An attempt to port MMU Linux to S31's architecture (RV32IMAFBCNSUX). Module tested: ESP32-S31-WROOM-3 E1H16R16V (ESP32-S31 Core Board). Example boot log Build/Flash Instructions Refer to the Build Instructions. Porting progress General Feature Status Buildroot rootfs 🟡 Untested Wireless (ESP-Hosted) 🟡 Untested Reboot and poweroff 🟡 Untested Dual hart SMP ⚫ Not Planned (Used by FreeRTOS) Peripheral Drivers Feature Status AXI GDMA 🟡 Untested AHB GDMA 🟡 Untested Cache driver 🟡 Untested TRNG 🟡 Untested eFuse 🟡 Untested Watchdog 🟡 Untested PWM, counter, analog peripherals 🟡 Untested CLIC/CLINT interrupt driver 🟡 Untested Flash MTD driver 🟡 Untested Timers 🟠 WIP Clock tree 🟠 WIP Security accelerators 🟠 WIP LP subsystem & IPC 🔴 Not Implemented PMP/APM 🔴 Not Implemented (properly) Connectivity Drivers Feature Status UART0 console 🟡 Untested UART1/2 🟡 Untested GMAC Ethernet 🟡 Untested SDMMC 🟡 Untested GPIO 🟡 Untested pinctrl/GPIO Matrix 🟡 Untested USB 🟠 WIP I2C 🔴 Not Implemented I2S 🔴 Not Implemented SPI 🔴 Not Implemented RMT 🔴 Not Implemented USB Serial/JTAG ⚫ Not Planned (Used by FreeRTOS) 🟢 Stable — Fully tested and working | 🟡 Untested — Seems working; not throughly tested | 🟠 WIP - Functions not fully implemented Also check out these command outputs. S31 Quirks (For more hardware references, see docs/ folder) This port was done before S31 TRM is available, therefore these guessworks were made: CLIC v. PLIC v. CLINT S31 uses CLIC and CLINT similar to P4. Linux expects PLIC. Therefore a custom CLIC driver is needed. I referenced this CLIC patch from disdi to get the CLIC working. Also, standard RISC-V interrupt CSRs are not usable, presumably because, from P4's TRM, CLINT interrupts are routed to CLIC and mtvec.MODE is hardwired to 0x3 (CLIC mode). Patches needed to make OpenSBI interrupts work. S mode S31's supervisor mode is not standard and has absolutely no usage in ESP-IDF so a lot of these CSR uses were mostly guessed from either P4's TRM or CSR probing (see docs/). For example, the use of sclicbase(?) and the lack of sie. S31 implemented SCLIC (Supervisor CLIC?) which is confusing since there is no known standardization; According to all laws of esp-idf, mcliccfg.NMBITS is not writable. IT IS WRITABLE! And setting it to 0b01 enables writes to the clicintattr[i].MODE field and thus enabling the use of S-mode interrupts. OpenSBI and Linux XIP To save the precious 16MB PSRAM memory, OpenSBI was modified to use XIP in flash and internal SRAM (hence the 3915901 KB firmware size in OpenSBI banner, since flash and SRAM mappings are not continuous). In mainline linux, XIP support on RISC-V was removed, so 6.12 was used instead which has proper XIP support. Appendix (as of 7/21/26) ~ # coremark 2K performance run parameters for coremark. CoreMark Size : 666 Total ticks : 18887 Total time (secs): 18.887000 Iterations/Sec : 1058.929422 Iterations : 20000 Compiler version : GCC15.2.0 Compiler flags : -O2 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -O2 -g0 Memory location : Please put data memory location here (e.g. code in flash, data on heap etc) seedcrc : 0xe9f5 [0]crclist : 0xe714 [0]crcmatrix : 0x1fd7 [0]crcstate : 0x8e3a [0]crcfinal : 0x382f Correct operation validated. See README.md for run and reporting rules. CoreMark 1.0 : 1058.929422 / GCC15.2.0 -O2 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -O2 -g0 / Heap # cat /proc/cpuinfo processor : 0 hart : 0 isa : rv32imafc_zicntr_zicsr_zifencei_zca_zcf_zbb mmu : sv32 uarch : espressif,esp32s31 mvendorid : 0x612 marchid : 0x80000003 mimpid : 0x1 hart isa : rv32imafc_zicntr_zicsr_zifencei_zca_zcf_zbb # uname -a Linux (none) 6.12.0-00036-gdccf9c1b2c4f-dirty #30 Thu Jul 2 23:48:23 CST 2026 riscv32 # free -h total used free shared buff/cache available Mem: 15004 1892 12784 0 328 12108 Swap: 0 0 0 # ps -aux 1 0 380 S /bin/sh -i 2 0 0 SW [kthreadd] 3 0 0 SW [pool_workqueue_] 4 0 0 IW [kworker/0:0-eve] 5 0 0 IW< [kworker/0:0H] 6 0 0 IW [kworker/u4:0-ev] 7 0 0 IW< [kworker/R-mm_pe] 8 0 0 SW [ksoftirqd/0] 9 0 0 SW [kdevtmpfs] 10 0 0 IW< [kworker/R-inet_] 11 0 0 SW [oom_reaper] 12 0 0 IW< [kworker/R-write] 13 0 0 SW [kcompactd0] 14 0 0 IW< [kworker/R-kbloc] 15 0 0 SW [kswapd0] 16 0 0 IW [kworker/0:1-pm] 17 0 0 IW [kworker/u4:1-ev] 18 0 0 SW [khvcd] 19 0 0 IW< [kworker/R-mld] 20 0 0 IW< [kworker/R-ipv6_] 34 0 380 R ps -aux # cat /proc/meminfo MemTotal: 15004 kB MemFree: 12788 kB MemAvailable: 12112 kB Buffers: 0 kB Cached: 328 kB SwapCached: 0 kB Active: 4 kB Inactive: 32 kB Active(anon): 4 kB Inactive(anon): 32 kB Active(file): 0 kB Inactive(file): 0 kB Unevictable: 328 kB Mlocked: 0 kB SwapTotal: 0 kB SwapFree: 0 kB Dirty: 0 kB Writeback: 0 kB AnonPages: 52 kB Mapped: 208 kB Shmem: 0 kB KReclaimable: 0 kB Slab: 756 kB SReclaimable: 0 kB SUnreclaim: 756 kB KernelStack: 352 kB PageTables: 24 kB SecPageTables: 0 kB NFS_Unstable: 0 kB Bounce: 0 kB WritebackTmp: 0 kB CommitLimit: 7500 kB Committed_AS: 304 kB VmallocTotal: 524288 kB VmallocUsed: 12 kB VmallocChunk: 0 kB Percpu: 32 kB