Mesen-S is a cross-platform SNES emulator for Windows & Linux built in C++ and C#.
If you want to support this project, please consider making a donation:
This version is a hacked verion by Oziphanto(m) which adds some 64Tass support and new fetures to aid SNES Development. See Below
Development builds of the latest commit are available from Appveyor. For release builds, see the Releases tab on GitHub.
Warning: These are development builds and may be unstable. Using them may also increase the chances of your settings being corrupted, or having issues when upgrading to the next official release. Additionally, these builds are currently not optimized via PGO and will typically run a bit slower than the official release builds.
Windows:
Linux:
The latest version is available from the releases tab on GitHub.
Packages are available here: https://aur.archlinux.org/packages/mesen-s-git/
See COMPILING.md
Mesen is available under the GPL V3 license. Full text here: http://www.gnu.org/licenses/gpl-3.0.en.html
Copyright (C) 2019 M. Bibaud
This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with this program. If not, see http://www.gnu.org/licenses/.
The main this I've added is 64Tass labels and Breakpoint/watchpoint/assert support. To generate a tass file in the right format you need to assemble with --dump-label -l [rom name].tass the order is important.
The system will detect and autoload a tass file for you, as long as you have the auto load option enabled ( it is by default ).
This is done by having a label have BREAK in it, anywhere in it. for example
RESET
CLC
XCE
LDA #$01
STA $420D
JML RESETHi
RESETHi
_BREAK
This will add a breakpoint on RESETHi, sometimes you will want multiple breakpoints in a function/scope so you can just do
_BREAK
...code...
_BREAK2
etc. Be warned that anything with BREAK will trigger this so if you have
doOUTBREAK
...code...
this will flag a breakpoint.
doOutBreak
...code...
will not.
Welcome to "the best"(tm) feature of a SNES emulator ever. You will be shocked to discover it took till 2021 for this to happen.
_ASSERT_[condition]
It must be _ASSERT and the condition's are a sub set of what MESEN_S support with a custom encoding becaues label limits. This is a hack and a "mostly does most of the job most of the time" case not a "complete solves everything in the universe" solution.
I've added a few short cuts for you.
| id | what it does | what it looks like in the debugger |
|---|---|---|
| _a8 | this will make sure at this point in the code A is 8 bits in size | (PS & 32) == 32 |
| _a16 | this will amke sure at this point in the code A is 16 bits in size | (PS & 32) == 0 |
| _xy8 | this will make sure at this point in the code X and Y are 8 bits in size | (PS & 16) == 16 |
| _xy16 | this will make sure at this point in the code X and Y are 16 bits in size | (PS & 16) == 0 |
| _axy8 | this will make sure at this point in the code A, X and Y are 8 bits | (PS & 48) == 48 |
| _axy16 | this will make sure at this point in the code A, X and Y are 16 bits | (PS & 48) == 0 |
| _jsl | this will mostly detect that the last jump with return was a long | jslf == 1 |
| _jsr | this will mostly detect that the last jump was return was abs | jslf == 0 |
For example, you have a function like so
myButeFunc_aXY
LDA #$04
STA $2100
RTS
And you assume, beleive and hope that when anything calls this A will be 8 bits in size. But we all know it goes wrong, it happens. So now you do
myButeFunc_aXY
_ASSERT_a8
LDA #$04
STA $2100
RTS
Now if the CPU hits that code, and Status.M is 0 the assert will fire and tell you, No its not, you stuffed up, look at the call stack, work out where you came from and fix it.
It gets better, because you can do conditions as well.
| What you have to type because labels | what it actually does |
|---|---|
| _0x | $ ( yeah I hate it too but all I could think, you got a better one hit me up) |
| EQ | == |
| LT | < |
| LTE | <= |
| GT | > |
| GTE | >= |
| NE | != |
| AND | && |
| OR | || |
| LBRAC | ( |
| RBRAX | ) |
Lets imagine you have an array, that is index by X, it would be a same if the code got to it with an invalid X that is too far right?
LDA #0
_ASSERT_X_LT_16
STA label,X
Now if something calls this code or function and X is not what you think it is, the assert will fire.
I also added 2 new registers to the mix, don't know why there were missing but they were.
DBR and DP this means you can _ASSERT_DBR_NE_0x7e_AND_DBR_NE_0x7f to make sure that when you are using your code and writing to registers, you are not actually looking at the WRAM. And DP is the direct page, so if you have some code that needs it to be zero _ASSERT_DP_EQ_0 or if you have a function to assumes it has been moved to somewhere else then _ASSERT_DP_EQ_0x400 if it should be $400.
Please note all sub commands are "to lowered" before checking, so the _ASSERT must be upper case everything else can be upper, lower or mixed as you please. ie. _ASSERT_X_LT_16 = _ASSERT_x_lt_16 = _ASSERT_X_Lt_16 etc
The ASSERT_JSL and ASSERT_JSR cases, a horrible hack, that will probably work 99.98% of the time. What it does:
It sets a flag internally when it does a JSL and clears it when it does a JSR. Thus when you get to the destination you check if this flag was what you wanted.
The flaws:
- well IRQs/NMIs if they fire during the JSR/JSL read, then the interrupt will trash the state. I handle this of cause. What it does is on an IRQ it shift the internal flag to the left, and then back to the right on an RTI. Thus IRQ NMI etc all have their own flag.
- The register is only 16 bits, so you only get 15 levels of IRQ/NMI nesting before data is lost.
- It assumes a 1:1 relation ship between Interrupt and RTI. So if you do any fancy super stable double IRQ setups this will break this feature.
- this 1:1 is also broken if you fire an RTI as some other optimistation, or your codes goes walkies and fires 3 or 4 haphazzadly.
Usage
lMyFunc
_ASSERT_JSL
..code...
RTL
MyOtherFunc
_ASSERT_JSR
...code...
RTS
This is used to add read/write/redwrite breakpoints of a size to a variable. for example
MyVar .byte
_WATCH_READ_BYTE
it must start _WATCH and your sub options are, in any order you prefer
| option | meaning |
|---|---|
| LOAD | break upon read/load |
| READ | break upon read/load |
| STORE | break upon write/store |
| WRITE | break upon write/store |
| READWRITE | break upon write/store or read/load |
| WRITEREAD | break upon write/store or read/load |
| LOADSTORE | break upon write/store or read/load |
| STORELOAD | break upon write/store or read/load |
| BYTE | does nothing but makes you feel better |
| WORD | sets the range for 2 bytes worth |
| LONG | sets the range for 3 bytes worth |
Note the address it covers is -1 -> -3 from the label, as the label is after the label so in the file will have the address post the actuall fields address. This in the code I do -1/-2/-3 to get the start. This if you have a long and do _WATCH_READ_WORD this will break on the upper word of the long not the lower word of the long.
And again please not that the _WATCH must be upper case everything else is "to lowered" and hence you can just do _WATCH_load_long if you want.
Well not everybody is perfect and it maybe to late for your current project, I understand. Good news is tass format in how I use it is simple enough that you can easily fake it. Here is an except from a real one.
Bank80.asm:170:1: Bank80.mBG2SC = $800011
Bank80.asm:262:1: Bank80.SpriteEmptyVal = $808163
Bank80.asm:151:1: Bank80.MainLoop = $808104
Bank80.asm:202:1: Bank80.DMAZero = $80810f
Bank80.asm:185:1: Bank80.mWOBJSEL = $80002f
Bank80.asm:180:1: Bank80.mBG3VOFS = $800025
master.asm:130:9: Bank80.mBG3VOFS.lo = $800025
Now the MESEN-S import doesn't give two hoots about the path at the start, it just skips it, what does matter is the ' ' after it.
Thus dummy [label]=[address] is all you need to do. addres can be in hex with $ or decimal.