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retroarch_api_faker.lua
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-- SPDX-FileCopyrightText: 2023 Wilhelm Schürmann <[email protected]>
--
-- SPDX-License-Identifier: MIT
-- This script attempts to implement the basic functionality needed in order for
-- the LADXR Archipelago client to be able to talk to BizHawk instead of RetroArch
-- by reproducing the RetroArch API with BizHawk's Lua interface.
--
-- RetroArch UDP API: https://github.com/libretro/RetroArch/blob/master/command.c
--
-- Only
-- VERSION
-- GET_STATUS
-- READ_CORE_MEMORY
-- WRITE_CORE_MEMORY
-- commands are supported right now.
--
-- USAGE:
-- Load this script in BizHawk ("Tools" -> "Lua Console" -> "Script" -> "Open Script")
--
-- All inconsistencies (like missing newlines for some commands) of the RetroArch
-- UDP API (network_cmd_enable) are reproduced as-is in order for clients written to work with
-- RetroArch's current API to "just work"(tm).
--
-- This script has only been tested on GB(C). If you have made sure it works for N64 or other
-- cores supported by BizHawk, please let me know. Note that GET_STATUS, at the very least, will
-- have to be adjusted.
--
--
-- NOTE:
-- BizHawk's Lua API is very trigger-happy on throwing exceptions.
-- Emulation will continue fine, but the RetroArch API layer will stop working. This
-- is indicated only by an exception visible in the Lua console, which most players
-- will probably not have in the foreground.
--
-- pcall(), the usual way to catch exceptions in Lua, doesn't appear to be supported at all,
-- meaning that error/exception handling is not easily possible.
--
-- This means that a lot more error checking would need to happen before e.g. reading/writing
-- memory. Since the end goal, according to AP's Discord, seems to be SNI integration of GB(C),
-- no further fault-proofing has been done on this.
--
local socket = require("socket")
local udp = socket.udp()
udp:setsockname('127.0.0.1', 55355)
udp:settimeout(0)
while true do
-- Attempt to lessen the CPU load by only polling the UDP socket every x frames.
-- x = 10 is entirely arbitrary, very little thought went into it.
-- We could try to make use of client.get_approx_framerate() here, but the values returned
-- seemed more or less arbitrary as well.
--
-- NOTE: Never mind the above, the LADXR Archipelago client appears to run into problems with
-- interwoven GET_STATUS calls, leading to stopped communication.
-- For GB(C), polling the socket on every frame is OK-ish, so we just do that.
--
--while emu.framecount() % 10 ~= 0 do
-- emu.frameadvance()
--end
local data, msg_or_ip, port_or_nil = udp:receivefrom()
if data then
-- "data" format is "COMMAND [PARAMETERS] [...]"
local command = string.match(data, "%S+")
if command == "VERSION" then
-- 1.14 is the latest RetroArch release at the time of writing this, no other reason
-- for choosing this here.
udp:sendto("1.14.0\n", msg_or_ip, port_or_nil)
elseif command == "GET_STATUS" then
local status = "PLAYING"
if client.ispaused() then
status = "PAUSED"
end
if emu.getsystemid() == "GBC" then
-- Actual reply from RetroArch's API:
-- "GET_STATUS PLAYING game_boy,AP_62468482466172374046_P1_Lonk,crc32=3ecb7b6f"
-- CRC32 isn't readily available through the Lua API. We could calculate
-- it ourselves, but since LADXR doesn't make use of this field it is
-- simply replaced by the hash that BizHawk _does_ make available.
udp:sendto(
"GET_STATUS " .. status .. " game_boy," ..
string.gsub(gameinfo.getromname(), "[%s,]", "_") ..
",romhash=" ..
gameinfo.getromhash() .. "\n",
msg_or_ip, port_or_nil
)
else -- No ROM loaded
-- NOTE: No newline is intentional here for 1:1 RetroArch compatibility
udp:sendto("GET_STATUS CONTENTLESS", msg_or_ip, port_or_nil)
end
elseif command == "READ_CORE_MEMORY" then
local _, address, length = string.match(data, "(%S+) (%S+) (%S+)")
address = tonumber(address, 16)
length = tonumber(length)
-- NOTE: mainmemory.read_bytes_as_array() would seem to be the obvious choice
-- here instead, but it isn't. At least for Sameboy and Gambatte, the "main"
-- memory differs (ROM vs WRAM).
-- Using memory.read_bytes_as_array() and explicitly using the System Bus
-- as the active memory domain solves this incompatibility, allowing us
-- to hopefully use whatever GB(C) emulator we want.
local mem = memory.read_bytes_as_array(address, length, "System Bus")
local hex_string = ""
for _, v in ipairs(mem) do
hex_string = hex_string .. string.format("%02X ", v)
end
hex_string = hex_string:sub(1, -2) -- Hang head in shame, remove last " "
local reply = string.format("%s %02x %s\n", command, address, hex_string)
udp:sendto(reply, msg_or_ip, port_or_nil)
elseif command == "WRITE_CORE_MEMORY" then
local _, address = string.match(data, "(%S+) (%S+)")
address = tonumber(address, 16)
local to_write = {}
local i = 1
for byte_str in string.gmatch(data, "%S+") do
if i > 2 then
table.insert(to_write, tonumber(byte_str, 16))
end
i = i + 1
end
memory.write_bytes_as_array(address, to_write, "System Bus")
local reply = string.format("%s %02x %d\n", command, address, i - 3)
udp:sendto(reply, msg_or_ip, port_or_nil)
end
end
emu.frameadvance()
end