/* firmware for STM8S-microcontroller-based HDMI firewall programmer
 * Copyright (C) 2019-2021 King Kévin <kingkevin@cuvoodoo.info>
 * SPDX-License-Identifier: GPL-3.0-or-later
 */
#include <stdint.h>
#include <stdbool.h>
#include <stdlib.h>

#include "stm8s.h"
#include "main.h"
#include "i2c_master.h"
#include "eeprom_blockprog.h"

// blink RUN LED to show error
static bool led_error = false;

// set when the button is pressed
static volatile bool rw_button_pressed = false;

// AWU tick count
static volatile uint8_t awu_tick = 0;

// to store the current E-EDID (EDID + extension)
static uint8_t edid[256];

// function RAM (code in RAM)
uint8_t f_ram[112 + 5]; // use RAM_SEG size in main.map (plus some margin)

// function for saving EDID + extension to EEPROM, to put in RAM
bool (*ram_eeprom_blockprog)(const uint8_t* data, uint16_t length);

// size of RAM segment
volatile uint8_t RAM_SEG_LEN;

// get the size of the RAM segment
inline void get_ram_section_length() {
	__asm__("mov _RAM_SEG_LEN, #l_RAM_SEG");
}

// copy functions to RAM
bool ram_cpy() {
	get_ram_section_length();
	if (RAM_SEG_LEN > ARRAY_LENGTH(f_ram)) {
		return false;
	}
	for (uint8_t i = 0; i < RAM_SEG_LEN; i++) {
		f_ram[i] = ((uint8_t *)eeprom_blockprog)[i];
	}
	ram_eeprom_blockprog = (bool (*)(const uint8_t* data, uint16_t length)) &f_ram;
	return true;
}

// blocking wait (in 10 us steps, up to UINT32_MAX / 10)
static void wait_10us(uint32_t us10)
{
	us10 = ((us10 / (1 << CLK->CKDIVR.fields.HSIDIV)) * 1000) / 206; // calibrated for 1 ms
	for (volatile uint32_t t = 0; t < us10; t++); // burn energy
}

// verify (E-)EDID checksums
// the sum of the bytes (including checksum at the end) must be 0
static bool checksum_ok(const uint8_t* data, uint16_t length)
{
	uint8_t checksum = 0;
	for (uint16_t i = 0; i < length; i++) {
		checksum += data[i];
	}
	return (0 == checksum);
}

// return if the current EDID is valid
/* from HDMI 1.3a specification
 * All Sinks shall contain an CEA-861-D compliant E-EDID data structure.
 * A Source shall read the EDID 1.3 and first CEA Extension to determine the capabilities supported
by the Sink.
 * The first 128 bytes of the E-EDID shall contain an EDID 1.3 structure. The contents of this
structure shall also meet the requirements of CEA-861-D.
 *
 * HDMI 2.1 uses CTA-861-G
 * this uses EDID 1.4 structure
 * EDID 1.3/1.4 is 128 bytes long, and can point to 128 bytes extension
 * EDID 2.0 with its 256 bytes does not seem to be used in HDMI at all
 * DisplayID with its variable-length structure meant to replace E-EDID only seems to be used in DisplayPort
 * I have no idea how more than 1 extension is supported since technically the ROM is limited to 256 bytes
 */
static uint16_t edid_length(void)
{
	// check EDID 1.3/1.4 fixed pattern header
	if (0x00 != edid[0] || 0xff != edid[1] || 0xff != edid[2] || 0xff != edid[3] || 0xff != edid[4] || 0xff != edid[5] || 0xff != edid[6] || 0x00 != edid[7]) {
		return 0;
	}

	if (1 == edid[18]) { // EDID 1.3/1.4 128-byte structure
		if (checksum_ok(&edid[0], 128)) {
			if (0 == edid[126]) { // no extension
				return 128;
			} else { // extension available
				// the usual extension is CEA EDID Timing Extension (with extension tag 02), but we allow others
				// no idea how more than 1 extension is supported
				if (checksum_ok(&edid[128], 128)) {
					return 256;
				} else {
					return 0; // EDID is broken
				}
			}
		} else {
			return 0;
		}
	} else if (2 == edid[18]) { // EDID 2.0 256-byte structure
		if (checksum_ok(&edid[0], 256)) {
			return 256;
		} else {
			return 0;
		}
	}

	return 0;
}

// load EDID + extension from EEPROM
static void load_edid(void)
{
	for (uint16_t i = 0; i < ARRAY_LENGTH(edid); i++) {
		edid[i] = *(uint8_t*)(EEPROM_ADDR + i);
	}
}

// save EDID + extension in EEPROM
static bool save_edid(void)
{
	return ram_eeprom_blockprog(edid, edid_length());
}

// read EDID from I²C memory
// return if succeeded
static bool read_edid(void)
{
	const uint8_t address[] = {0};
	if (!i2c_master_setup(false)) {
		return false;
	}
	if (I2C_MASTER_RC_NONE != i2c_master_address_read(I2C_SLAVE, false, address, ARRAY_LENGTH(address), edid, ARRAY_LENGTH(edid))) {
		return false;
	}
	i2c_master_release(); // release I²C again
	return true;
}

// write EDID to I²C memory
// return if succeeded
static bool write_edid(void)
{
	const uint8_t address[] = {0};
	if (!i2c_master_setup(false)) {
		return false;
	}
	if (I2C_MASTER_RC_NONE != i2c_master_address_write(I2C_SLAVE, false, address, ARRAY_LENGTH(address), edid, edid_length())) {
		return false;
	}
	i2c_master_release(); // release I²C again
	return true;
}

void main(void)
{
	sim(); // disable interrupts (while we reconfigure them)

	CLK->CKDIVR.fields.HSIDIV = CLK_CKDIVR_HSIDIV_DIV0; // don't divide internal 16 MHz clock
	CLK->CKDIVR.fields.CPUDIV = CLK_CKDIVR_CPUDIV_DIV0; // don't divide CPU frequency to 16 MHz
	while (!CLK->ICKR.fields.HSIRDY); // wait for internal oscillator to be ready

	// save power by disabling unused peripheral
	CLK_PCKENR1 = CLK_PCKENR1_I2C; // keep I²C
	CLK_PCKENR2 = CLK_PCKENR2_AWU; // keep AWU

	// configure LEDs
	EDID_LED_PORT->DDR.reg |= EDID_LED_PIN; // switch pin to output
	EDID_LED_PORT->CR1.reg &= ~EDID_LED_PIN; // use in open-drain mode
	edid_led_off(); // start with LED off
	RUN_LED_PORT->DDR.reg |= RUN_LED_PIN; // switch pin to output
	RUN_LED_PORT->CR1.reg &= ~RUN_LED_PIN; // use in open-drain mode
	run_led_off(); // start with LED off

	// configure read/write button
	RW_BUTTON_PORT->DDR.reg &= ~RW_BUTTON_PIN; // switch pin to input
	RW_BUTTON_PORT->CR1.reg |= RW_BUTTON_PIN; // pull up
	RW_BUTTON_PORT->CR2.reg |= RW_BUTTON_PIN; // enable external interrupt
	EXTI->CR1.fields.PDIS = EXTI_FALLING_EDGE; // interrupt only on falling edges (WARNING hard coded port)

	// configure auto-wakeup (AWU) to be able to refresh the watchdog
	// 128 kHz LSI used by default in option bytes CKAWUSEL
	// we skip measuring the LS clock frequency since there is no need to be precise
	AWU->TBR.fields.AWUTB = 10; // interval range: 128-256 ms
	AWU->APR.fields.APR = 0x3e; // set time to 256 ms
	AWU_CSR |= AWU_CSR_AWUEN; // enable AWU (start only when entering wait or active halt mode)

	// load function in RAM
	ram_cpy();

	// configure independent watchdog (very loose, just it case the firmware hangs)
	IWDG->KR.fields.KEY = IWDG_KR_KEY_REFRESH; // reset watchdog
	IWDG->KR.fields.KEY = IWDG_KR_KEY_ENABLE; // start watchdog
	IWDG->KR.fields.KEY = IWDG_KR_KEY_ACCESS; // allows changing the prescale
	IWDG->PR.fields.PR = IWDG_PR_DIV256; // set prescale to longest time (1.02s)
	IWDG->KR.fields.KEY = IWDG_KR_KEY_REFRESH; // reset watchdog

	// erase saved EDID when button is pressed on boot
	if (0 == (RW_BUTTON_PORT->IDR.reg & RW_BUTTON_PIN)) { // button is pressed while booting
		for (uint16_t i = 0; i < ARRAY_LENGTH(edid); i++) {
			edid[i] = 0; // create empty EDID
		}
		ram_eeprom_blockprog(edid, ARRAY_LENGTH(edid)); // erase EDID
	}
	load_edid(); // load EDID from EEPROM
	bool edid_valid = (0 != edid_length()); // verify if EDID is valid

	rim(); // re-enable interrupts
	bool action = false; // if an action has been performed
	while (true) {
		IWDG_KR = IWDG_KR_KEY_REFRESH; // reset watchdog
		// handle button press
		if (rw_button_pressed) {
			wait_10us(100); // wait 1 ms for the noise to be gone
			if (0 == (RW_BUTTON_PORT->IDR.reg & RW_BUTTON_PIN)) { // ensure the button is pressed (the pull-up is really weak)
				wait_10us(10000); // debounce for 100 ms
				uint8_t press_duration = 1; // start counting how long the button is pressed
				while (0 == (RW_BUTTON_PORT->IDR.reg & RW_BUTTON_PIN)) { // wait until button is depressed
					wait_10us(10000); // wait for 100 ms
					press_duration++;
					IWDG_KR = IWDG_KR_KEY_REFRESH; // reset watchdog
				}
				led_error = false; // reset error state
				if (press_duration < 30) { // less than 3 sec
					run_led_on(); // indicate we started
					if (read_edid()) { // read EDID from I²C
						edid_valid = (0 != edid_length()); // verify if EDID is valid
						if (edid_valid) { // read EDID is valid
							IWDG_KR = IWDG_KR_KEY_REFRESH; // reset watchdog
							led_error = !save_edid(); // save to EEPROM
							IWDG_KR = IWDG_KR_KEY_REFRESH; // reset watchdog
						} else { // read EDID is not valid
							led_error = true; // indicate read error
							load_edid(); // re-load EDID from EEPROM
							edid_valid = (0 != edid_length()); // verify if EDID is valid
						}
					} else { // read error
						led_error = true; // indicate read error
						load_edid(); // re-load EDID from EEPROM
						edid_valid = (0 != edid_length()); // verify if EDID is valid
					}
					i2c_master_release(); // release I²C again
				} else { // button pressed > 3s
					run_led_on(); // indicate we started
					if (edid_valid) {
						led_error = !write_edid(); // write EDID to I²C EEPROM
					} else {
						led_error = true; // we can't program an invalid EDID
					}
				}
			}
			action = true; // remember we performed an action
			rw_button_pressed = false; // clear flag
		}
		// update LED
		if ((awu_tick & 0x7) < 4) { // on period of blink (every second)
			edid_led_on(); // on period
			if (led_error) {
				run_led_on(); // start blinking
			}
		} else {
			if (!edid_valid) { // EDID not valid
				edid_led_off(); // blink to let user know
			}
			if (led_error) {
				run_led_off(); // blink to indicate error
			}
		}
		if (action) { // something has been performed, check if other flags have been set meanwhile
			action = false; // clear flag
		} else { // nothing down
			wfi(); // go to sleep (wait for any interrupt, also starting AWU)
		}
	}
}

void awu(void) __interrupt(IRQ_AWU) // auto wakeup
{
	volatile uint8_t awuf = AWU_CSR; // clear interrupt flag by reading it (reading is required, and volatile prevents compiler optimization)
	awu_tick++; // increment tick count
	// let the main loop kick the dog
}

void rw_button_isr(void) __interrupt(IRQ_EXTI3) // button pressed
{
	rw_button_pressed = true; // notify main loop
}