Embedded targets

NURL compiles to LLVM IR with no target triple baked in. This makes it reachable on bare-metal targets. It reaches them the same way it reaches any cross-compile target. Hand the IR to the right backend. stdlib/hal/ holds the hardware-facing layer this needs.

Memory-mapped I/O

stdlib/hal/mmio.nu You use this primitive to build every register-level driver. It reads or writes a 32-bit word at a fixed physical address.

( mmio_read32  i addr )          → i    // load  *(u32*)addr
( mmio_write32 i addr i32 val )  → v    // store *(u32*)addr = val
( mmio_set32   i addr i32 mask ) → v    // *(u32*)addr |= mask
( mmio_clear32 i addr i32 mask ) → v    // *(u32*)addr &= ~mask

These compile to LLVM's load volatile / store volatile. The optimizer never hoists, reorders, or coalesces an MMIO access. A spin on a device status register is correct at any optimization level. It is pure IR with no runtime call. It works on a freestanding target with no OS underneath it.

ESP32

stdlib/hal/esp32.nu is a register-level HAL for the classic ESP32 (Xtensa). You build it entirely on mmio.nu. There is no ESP-IDF. There is no FFI beyond the memory-mapped registers themselves. Register addresses are cross-checked against Espressif's technical reference manual.

( esp32_gpio_enable_output i mask ) → v   // drive these pins as outputs
( esp32_gpio_set   i mask ) → v            // set pins high
( esp32_gpio_clear i mask ) → v            // set pins low

( esp32_uart_putc i ch ) → v               // blocking write, UART0
( esp32_uart_getc )      → i               // blocking read, UART0

Both CPU families on the chip are covered, through two different toolchains:

The Xtensa path has been flashed to real ESP32 silicon. It is verified over serial. A GPIO blink uses only NURL's register writes. A call crosses from C into NURL and back. examples/esp32/ has both paths. idf-blink/ is a complete ESP-IDF project. All GPIO access is NURL. C supplies only app_main. blink.nu targets the RISC-V chips directly through stock LLVM. It needs no vendor fork.

Next

• Platforms — the rest of NURL's cross-compile targets.
• Build steps, prerequisites, and both toolchains in full are in examples/esp32/README.md.