Add full flash XIP support for ESP32, enabling code and read-only data to
execute/load directly from flash via the MMU cache rather than consuming
precious SRAM. This increases available RAM from ~328KB to effectively
unlimited for code/rodata, while keeping ~121KB for the Go heap.
Changes:
- src/device/esp/esp32.S: Add MMU initialization in call_start_cpu0
- Call ROM bootloader mmu_init() and cache_flash_mmu_set() to map DROM/IROM
- Enable flash cache via ROM Cache_Read_Enable()
- Fix tinygo_scanCurrentStack to spill all register windows for GC
- targets/esp32-interrupts.S: Add exception diagnostics
- targets/esp32.ld: Major linker script restructure for XIP
- Add DROM (4MB @ 0x3F400000) and IROM (4MB @ 0x400D0000) regions
- Move .rodata to DROM, main .text to IROM (both flash-mapped)
- Keep boot code, vectors, and WiFi blob IRAM sections in SRAM0
- Create WiFi arena in SRAM1 pool 7/6 (64KB @ 0x3FFF0000)
- Move .bss and heap to SRAM2 (200KB @ 0x3FFAE000), avoiding ROM/MAC regions
- Add _drom_flash_addr variable (patched by builder with flash offset)
- targets/esp32.json: Add linker wrap flags for malloc/free and WiFi functions
Signed-off-by: deadprogram <ron@hybridgroup.com>
This is only very minimal support. More support (such as tinygo flash,
or peripheral access) should be added in later commits, to keep this one
focused.
Importantly, this commit changes the LLVM repo from llvm/llvm-project to
tinygo-org/llvm-project. This provides a little bit of versioning in
case something changes in the Espressif fork. If we want to upgrade to
LLVM 11 it's easy to switch back to llvm/llvm-project until Espressif
has updated their fork.
deadprogram
Ayke van Laethem