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mGBA 0.10.3 GDB stub watchpoint in IWRAM causes DMA1 FIFO A underrun & drift

Wed, 07 Oct 2026 20:58:10 +0000

Hi everyone,

While debugging a custom GBA Thumb audio mixer routine in mGBA 0.10.3 (macOS arm64 Qt6 build) using

Code:
arm-none-eabi-gdb

connected to the built-in GDB stub (

Code:
localhost:2345

), I noticed that setting a 32-bit hardware write watchpoint (

Code:
Z2

packet) inside IWRAM (

Code:
0x03004B20

) causes a consistent +516 cycle drift on

Code:
mTimingNextEvent

and triggers a

Code:
GBAAudioScheduleFifoDma: FIFO A empty on Timer 0 overflow!

pop every time execution resumes with

Code:
continue

.

Here is a screenshot of the ARM7TDMI register/watchpoint state alongside the

Code:
arm-none-eabi-gdb

and mGBA console output:

Direct image: https://files.media2url.com/free/18d03c01ee3447.png (uploaded via https://media2url.com/screenshot-to-url — full view: https://media2url.com/m/18d03c01ee3447)

Reproduction steps:
1. Configure Timer 0 (

Code:
REG_TM0CNT_L = 0xFE80

, prescaler 1) driving Direct Sound FIFO A (

Code:
0x040000A0

) via DMA1 (

Code:
0xB640

).
2. Attach

Code:
arm-none-eabi-gdb

Code:
localhost:2345

and set a write watchpoint on the mixer channel position in IWRAM:

Code:
(gdb) target remote localhost:2345

(gdb) watch *(uint32_t*)0x03004b20

(gdb) c

3. When the watchpoint traps inside

Code:
SoundMainRam_Thumb

(

Code:
PC = 0x03001A44

) and we resume with

Code:
c

Code:
_GBAVideoSoftwareRenderer

logs that

Code:
LY=161

VBlank IRQ is delayed by ~516 cycles and Timer 0 misses 4 overflow ticks before DMA1 refills

Code:
REG_FIFO_A

.

Does the GDB stub pause

Code:
mTiming

sub-instruction DMA/Timer scheduling differently when trapping on an IWRAM data watchpoint (

Code:
_GBAMemoryWatchpoint

) vs. an instruction breakpoint (

Code:
Z0

), or is there a flag to freeze Timer 0 ticks while the stub is halted mid-scanline?

Thanks in advance!

mGBA Appreciation <3

Sat, 26 Sep 2026 08:34:14 +0000

I just wanted to share that I love this emulator, and the dev is awesome for working on this!

I am just glad to know that I'm using an emulator that I can believe in, and not some AI coded shit like some other emulators are (sorry to muddy this message by throwing shade).

Anyways thanks endrift <3

yayCollie (she/her)

Palette changing when applying settings

Fri, 25 Sep 2026 16:06:04 +0000

So, I know it's intended that the palette set in the Game Boy settings gets applied when you press "ok" or "apply", but I kinda would rather just keep the one loaded from the ROM and can't for the life of me figure out a way to do that.

It is a little annoying to have to reload the ROM every time I change a setting.

Anyone know a way to fix this annoyance?

Feature request: Always on top

Wed, 09 Sep 2026 05:31:33 +0000

Always on top is allows the user to click around on their desktop while not changing the active window. I've used several emulators that allow this, is there any way we could get the feature?

(0.10.5) Trouble with provided socketserver.lua & sockettest.lua

Tue, 18 Aug 2026 03:38:30 +0000

Hello I have recently started messing around creating lua scripts and wanted to do some stuff with sockets and so tried the included scripts but anytime sockettest.lua connects it disconnects instantly.

Running sockettest without modification gives this output with the error on repeat:
Socket Test: Connecting to 127.0.0.1:8888...
Socket Test: Connected
Socket Test: Shutting down
Socket Test: Connecting to 127.0.0.1:8888...
[ERROR] D:/Emulation/mGBA/scripts/sockettest.lua:29: attempt to concatenate a table value (local 'err')

so i tried changing the error displaying in ST_error to this so i could get some info:
for i = 0, #err, 1
do
console:error(string.format("(Line %d) Socket Test Error: %s", i+1, err[i]))
end

Which gave me this output instead:
Socket Test: Connecting to 127.0.0.1:8888...
Socket Test: Connected
Socket Test: Shutting down
Socket Test: Connecting to 127.0.0.1:8888...
Socket Test: Connected
[ERROR] (Line 1) Socket Test Error: nil
Socket Test: Shutting down

For reference the output on socketserver.lua is this:
Socket Server Test: Listening on port 8888
Socket 1 Received: Connected
[ERROR] Socket 1 Error: disconnected
Socket 2 Received: Connected
Socket 2 Received: [ ]
[ERROR] Socket 2 Error: disconnected

I did try running the scripts on the dev build (0.11.0) and didn't have any such issues there, but I had problems with the emulator not responding when going to load a rom or script so idk lmao. Any help with this would be greatly appreciated ty <3

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Sun, 28 Jun 2026 17:35:13 +0000

Pokemon this, pokemon that. it's like people don't realise OTHER GAMES EXIST!

Lufia - The Ruins of Lore
Lufia - The Legend Return
Dragon Warrior Monsters
Dragon Warrior Monsters 2: Cobi's Journey
Dragon Warrior Monsters 2: Tara's Adventure

Are some games I've been playing and trying to get the Link setup has been a damned nightmare. I remember YEARS ago, yea with pokemon, an emulator had a visual indicator like the old Link Cable, to show the two windows were connected. It was pleasent.

However right now all I have is guess work and 10,000 god damned guides on how to setup an emulator, but no one can make a simple guide showing how to link things together that ISNT fucking pokemon.

Can someone actually think for once and stop beating off to copy-paste guides and pokemon and help me get linking working for some ACTUAL games.

Yeah I'm frustrated, get over it.

Can you launch mGBA straight into a game via a shortcut?

Tue, 23 Jun 2026 16:17:13 +0000

This is a Windows question. Other emulators can launch straight into the game via startup options added to a shortcut or alternate configuration files.

I was wondering if there is an option to achieve this in mGBA as well. I've looked online and through the forum, but couldn't find anything.

don't know what happened to my save file for FireRed

Mon, 15 Jun 2026 20:05:45 +0000

hello,

I had been playing through FireRed on mGBA and have always just saved through the actual game menu. I had no idea about .sav files until just now.

I saved the game the last time I played it, but now when I open the game, it brings me to a new save file. I don't know if my previous save got deleted or if I just can't find it.

I'm pretty sure that my file was the one attatched in the photo below, but it gives me an error message.

I'm completely a beginner when it comes to ROMs so any help would be appreciated

Screenshot 2026-06-15 at 2.50.21 PM.png (Size: 129.58 KB / Downloads: 0)

Game & Watch Gallery 4 Link Cable not working

Mon, 18 May 2026 04:45:16 +0000

Hi everyone! I've earned 200 stars in Game & Watch Gallery 4. Unfortunately, to get the last 20 stars, I need to play multiplayer via Link Cable. I've opened two emulator sessions, but the game doesn't recognize that I'm connected via Link Cable. Please help!

How to unfreeze my pokemon emerald ROM

Sun, 26 Apr 2026 14:02:22 +0000

Was looking for a solution to "unfreeze" my game. I didnt save and now I will lose all my progress unless there is a way to fix this freezing issue. Game froze when I started talking to an NPC. Am I cooked?