Immutable ROM FW Integration

OCAH contains three immutable ROM FW images: the SMC production ROM FW, the SEP production ROM FW, and the Key Manager application ROM FW. Each image has two integration contracts. The adopter connects and configures the corresponding ROM macro, and the final ROM FW image must be present before its processor leaves reset. Where ROM FW must initialize or access an adopter-owned peripheral outside OCAH, the image may also expose build-time integration hooks.

The firmware itself is described in the Programmer’s Guide appendices: the SMC Boot ROM, the SEP Boot ROM, and the Key Manager Application ROM.

1. Weak-symbol override method

An immutable ROM FW image may provide selected vendor-neutral integration hooks as weak symbols. Supply an adopter implementation as a strong definition of the same symbol before the final image is frozen. The strong implementation must program the same adopter-owned IP instantiated by the RTL integration, and its signature, ABI, return values, and documented semantics must match the weak declaration.

This mechanism applies only when the ROM FW needs to interact with a peripheral outside OCAH. It is a build-time image-composition mechanism, not a runtime extension mechanism. Include the adopter implementation in the final ROM FW build so that it replaces the weak definition at link time.

Inspect the final ELF or linker map after linking. For example, riscv64-unknown-elf-nm must report each selected implementation as a strong symbol rather than W; successful linking alone does not prove that the weak default was replaced.

2. SMC ROM FW integration

Connect smc_rom_intf_req_o and smc_rom_intf_rsp_i to the adopter’s ROM implementation. In the current four-core configuration, the request provides the ROM clock, enable, and 14-bit 64-bit-word address, and the response returns one 64-bit word. This is a direct memory interface, not AXI-Lite. The 128 KiB ROM FW image must be present before the first boot; its build is under hw/sys/smc/bootrom/prod/.

Connect the ROM macro configuration input reached as rom_cfg_i and mem_cfg_i according to the selected macro’s contract. OCAH forwards these 11 bits without assigning technology-specific semantics; the reference smc_ip_integration.sv ties them to zero. Set the eFuse shadow value that drives the CPU’s rom_flip_endianness_i path to match the byte order of the image and ROM macro. Deasserted passes each 64-bit read word unchanged; asserted reverses its eight bytes.

Table 1. SMC ROM FW override inventory
Hook	Weak default	Rationale	Override and integration action
`smc_pll_init()`	Returns `SMC_PLL_SUCCESS` without programming PLL hardware.	PLL implementation is technology- and vendor-specific, so OCAH does not include a vendor-specific PLL driver.	Override when `BL0_PLLCLK` is asserted and the adopter’s PLL requires ROM-time configuration. Provide the same `smc_pll_result_t smc_pll_init(void)` signature in the final ROM FW build. Any result other than `SMC_PLL_SUCCESS` is fatal: the ROM FW records an interface error and remains in `wfi`.
`i3c_release_reset()`, `cfg_ps()`, `init_i3c_ctrl()`, and `I3C_GetDriverInstance()`	Permit the ROM FW to boot without an active I3C implementation; I3C data operations report a hardware error.	OCAH includes an I3C implementation, but the adopter may select a different I3C target and driver for the final system.	When the ROM FW must use an active I3C target, select the open HCI implementation with `I3C_CORE=chipsalliance`, or connect the adopter’s I3C target through the SMC external AXI-Lite master (`smc_external_req_o` and `smc_external_resp_i`) and link strong implementations that conform to `drivers/include/i3c_target_driver.h`.

3. SEP ROM FW integration

The SEP exposes the sep_boot_rom memory interface for its production ROM FW image. The detailed ROM-macro configuration, image-loading contract, and adopter override inventory are not yet documented here.

Table 2. SEP ROM FW override inventory
Hook	Status
To be documented	No adopter override requirement is defined here yet.

4. Key Manager ROM FW integration

The Key Manager exposes the km_rom_mem interface through SEP for its application ROM FW image. The detailed ROM-macro configuration, image-loading contract, and adopter override inventory are not yet documented here.

Table 3. Key Manager ROM FW override inventory
Hook	Status
To be documented	No adopter override requirement is defined here yet.