People keep asking me how to use SDK functions (e.g. system_get_rst_info) in rBoot so they can add interesting new features. The simplest answer is you can’t – if you want to use the full set of SDK features you would need to link rBoot against the SDK, it’s size would go from <4k to >200k and it wouldn’t actually be possible to chain load a user rom. The less simple answer is if the SDK functions are simple enough and can be reverse engineered then you can replicate them in rBoot, or any other bare-metal app. So some simple things will be possible, with work, but you’ll never be able to use more complex features like wifi from rBoot.

Here is C code to replicate the system_get_rst_info. Note that it passes back a structure rather than a pointer to one (the SDK creates and stores this structure at boot and later just passes a pointer to it when requested, but the code below creates it when needed). Also note that you cannot use this code after the SDK has started because the SDK resets this information when it boots, but it will work just fine in rBoot.

struct rst_info {
	uint32 reason;
	uint32 exccause;
	uint32 epc1;
	uint32 epc2;
	uint32 epc3;
	uint32 excvaddr;
	uint32 depc;
};

struct rst_info system_get_rst_info() {
	struct rst_info rst;
	system_rtc_mem_read(0, &rst, sizeof(struct rst_info);
	if (rst.reason >= 7) {
		ets_memset(&rst, 0, sizeof(struct rst_info));
	}
	if (rtc_get_reset_reason() == 2) {
		ets_memset(&rst, 0, sizeof(struct rst_info));
		rst.reason = 6;
	}
	return rst;
}