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Page: Implementing ipatix's High Quality Audio Mixer
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Ability Switcher via special Add A PokeVial Item Add Ability to Avoid Battle Damage in Debug Menu Add Ability to Swap Bikes Whenever Add Choice Specs Scarf hold item effects Add Description Submenu Add Difficulty Mode Add In‐Cart Rumble Add Nuzlocke Challenge Add PC Access in PokeNav Add Physical Special Split Add Sleep Mode Add Thief Ball Add a EV IV Stat Editor UI Add a debug menu Adding Multi region Support Adding Support for Connectivity with Other Hacks Whilst Maintaining Connectivity with Vanilla Adding Time Based Encounters Adding Walking Animations to All NPCs Adding a New Trainer Class Adding a New Trainer Front Picture Adding a Pokémon Type & Disabling the Mystery Type Adding new event object or overworld sprites All Trees Permanently Get Cut Allow All Pokemon to Evolve Without Trading Allow Both Latios and Latias Appear. Allow Feebas to be caught on any Valid Fishing Spot in Route 119 rather than only Three Allow Jumping Over Ledges with Acro Bike Allow Move Relearner to Teach Moves that Pre Evolutions Know Allow Running From Trainer Battles Allow running indoors Amulet Coin Effects If Anyone In Party is Holding It Automatically make the keyboard switch to lowercase after the first character Better White Out Money Calculation Button Press to Skip Copyright Screen Chain Fishing Change Enemy Trainer Parties Depending on Difficulty Change Someone's PC to Lanette's PC from the Start of the Game Change Starter Pokémon Change Time Based Evolution Times Change initial PC items Changing the Battle Music Depending on the Opponent Colored stats by nature in summary screen Converting to FR Tilesets Custom Battle Mugshots Custom Border Dimensions Debugging using gdb (Windows, WSL2, Visual Studio Code mGBA) Debugging using printf Disable Bag Use In Battle Disable Catching Pokemon Disable Pokémon animation on Birch's intro Pokémon Disabling Union Room check when entering Pokémon Centers Dynamic Trade Names Dynamic overworld palette system Enable the Reset RTC Feature Enable trade with FRLG without beating the game Expanding The Metatile Count Extra save space with three lines of code Faster HP Drain Feature Branches Fish Will Now Always Get on Hook Fix AI's Switch In Battle Fix Snow Weather Fixing the aspect ratio of the Pokémon logo on the title screen Forcing Battle Animations for Major Battles Full Screen Start Menu by Archie and Mudskip Gen 6 Exp Share Gen 6 style Exp. Share Alternative Option Get Match Calls Only If Caller Wants a Rematch Get Rid of Battery Run Dry Error Message Get Rid of Pokemon Disobeying You Holding Select Allows For A Second Register Item Home How the Game Works How to Support Savefile Backwards Compatibility How to add a new Pokémon species How to add a new ability How to add a new region map How to create a new regular trainer battle How to delete a map Implement Missing Text Function RESET_FONT Implementing Catch EXP Implementing ipatix's High Quality Audio Mixer Implementing the “textcolor” script command from FRLG and give object events their own text colour Improve Partner Battle Code Improve the Loading of Battle Terrain Improving the WaitForVBlank function Increase money limit Infinite TM usage Instead of Asking to Stop learning a New Move, You'll be Asked to Continue Learning Item Automatically Goes to PC if Bag is Full Keep the Camera from Making Waves LGPE Style Bonus Premier Balls Learn moves upon evolution List Menu Text Coloring Make Cleanse Tag Avoid All Wild Encounters and Usable If Held By Anyone in Your Party; Make PokeDoll Do the Same for Trainers Seeing You Make Daycare Faster at Leveling Pokémon Make Key Items That Cannot Be Used In The Field Not Show A Use or Register Option Make L Button Be Turbo A When L=A Option Is Set Make Ledge Jumps Check Collision Make Move Relearner Teach Egg Moves With A Flag Make Multiple Secret Bases Make Norman's Slaking Have Ability Intimidate Make Pokemon Not Heal When Going into PC Make Pokemon that Require a Fateful Encounter to be Legal to Always Be Set to Legal Make space for EWRAM Data for Summary screen Make the Bag Able to Hold 120 Items Instead of 30 Make the Person in the Intro Match the the Save File Map Based Trainer Battle Music Move Item Multipage Options Menu Name Rater Allows Traded Pokemon to be Renamed New Birch's Briefcase With Fully Custom Starters by Archie and Mudskip New Custom Menu Border Themes (Basic) New Main Menu UI With Mugshot by Archie and Mudskip New Options Plus ‐ Multipage Options Menu with Faster Text, HP‐EXP Bar Speeds and Metric Nickname your Pokémon from the party menu Not showing dex entries until getting the Pokédex Omnidirectional Jump Optimization ‐ Remove Expensive and Redundant `BuildColorMaps()` Function Option to Skip Copyright and Intro Overview: Items and their Effects Overview: The Party Menu Overview∶ The Game Loop Overview∶ The Task System Per Shop\Mart Item Prices Plural Giveitem Pokecenters Disregard Eggs Prompt for reusing Repels Push B in wild battle moves to Run Push B to Toggle Running Shoes Pushing B When Asked To Stop Learning Move Will Cancel Teaching The Move Quickly Run from a Battle by Holding Right While the Wild Pokémon's Name Appears Raise Odds of Catching a Pokemon by Pressing B When the Ball Shakes Random Info, Tips, and Tricks Reflections Remove 'Select' Sound From Specific Map Events Remove Warp Fadescreen Remove badge boosts Remove the backup save file Remove the extra save confirmation Remove the functionally redundant move grammar tables Repeated Field Medicine Use Reuse filler save space for Variables and Flags Revert Brendan May Sprites to Ruby Sapphire Set Metatile IDs From Another Map Set Up Item Balls on a Map Without Needing New Scripts Shifting to Pokémon Already in Battle Exits the Shift Menu Shiny Creation With a Flag Shop Items By Badge Count Show IVs EVs in Summary Screen Show Species That You're Switching For in the Party Menu Show Type Effectiveness In Battle Using Pre Existing Function and Disable in Option Menu Show a throbber animation while the game is saving Shuckle makes Berry Juice Something doesn't work I need help etc. Spawn Invisible Player Speedy Nurse Joy Spinda Second Frame Spot Addition Stair Warps Supplementary Scripting Macros Surfing Dismount Ground Effects Temporarily Replace Player or Enemy Party Pokemon The Basics of Scripting Toggle Trainer Sight Trainer Backsprite Editing Trainer Class Based Poké Balls Trainer Scripts Trainers No Longer Spin to Face You Right As You Pass Them Trigger Map Scripts By Flag Triple layer metatiles Tutorials Tweaking the count of health beeps Uniquely Shuffle Array Update Sitrus Berry's effect to Gen 4 standard Use HMs Without Any Pokemon in your Party Knowing Them Useful Modding Tools Useful Scripting Specials Why You Should (Almost) Always Be Using 32‐Bit Variables in Your Code Why should I use this over binary hacking
0 Implementing ipatix's High Quality Audio Mixer
FieryMewtwo edited this page 2021-12-20 09:41:45 -05:00
Table of Contents

Preface

All GBA games use the sound driver that comes in the GBA SDK, m4a (also known as mp2k or "Sappy"). While not a bad engine, it does have the issue of being notoriously noisy. In response to this, ipatix created a custom audio mixer for use in the m4a engine based on the custom engine of the Golden Sun games. This engine has two major benefits:

  1. Less noise. The SDK's audio mixer mixes every channel in 8-bit before also outputting at the final 8-bit DAC. What this means is that every additional DirectSound channel will add more noise, and with enough channels it can get pretty bad. This mixer avoids that issue by mixing the audio in a 16-bit space so that the only conversion to 8-bit is at the final DAC output; this means that no matter how many channels you have, the amount of noise will be the same (equivalent to having a single channel worth of noise in the original mixer).
  2. Better performance. The code is highly optimized and contains a self-modifying code loop that is loaded into RAM and allows for faster processing than the SDK mixer, even despite the new 16-bit arithmetic. For more details on how the mixer itself actually works, visit ipatix's repository for the mixer. However, none of this information is necessary if you just want to use it in your game, and with that said, we can now move on to the actual tutorial.

Implementing the Mixer

Replacing the Mixer Code

Replace the src/m4a_1.s file with this one. This is a rewritten version of the file with a version of ipatix's mixer already inserted. The version in this file has been tailored specifically for pokeemerald and thus is slightly different than the version on his repository.

In src/m4a.c, change the size of SoundMainRAM_Buffer to 0xB40. This buffer is where the code itself is loaded into. Still in src/m4a.c, add this line right below the line mentioned above:

BSS_CODE ALIGNED(4) u32 hq_buffer_ptr[size] = {0};

This is the intermediate audio buffer in which the mixing will be done. With the aforementioned changes, the lines should look like this:

BSS_CODE ALIGNED(4) char SoundMainRAM_Buffer[0xB40] = {0};
BSS_CODE ALIGNED(4) u32 hq_buffer_ptr[size] = {0};

Here, [size] is the length of one frame of audio, which varies by the sample rate you use. Here is a list of the possible sample rates and their corresponding frame sizes:

5734Hz: 0x60
7884Hz: 0x84 (This mode is not aligned to the buffer length and is not supported by the mixer)
10512Hz: 0xB0
13379Hz: 0xE0 (This is the default engine rate; without any modifications, this is what the GBA Pokemon games use)
15768Hz: 0x108
18157Hz: 0x130
21024Hz: 0x160
26758Hz: 0x1C0
31536Hz: 0x210
36314Hz: 0x260
40137Hz: 0x2A0
42048Hz: 0x2C0

Find the sample rate you are using and use its corresponding frame size as the size of the array. For example, for the default sample rate, the size of the array is 0xE0 (note that the size of the array actually needs to be the frame size x 4; this is why this array is of type u32 rather than char or u8).

We have finished "inserting" the mixer, but DO NOT COMPILE YET. It will fail, and that is because... we are out of memory!

Making Room in RAM

The one downside to the new mixer is that it does require more RAM than the default mixer due to the increased code size and additional mixing buffer. IWRAM is precious in GBA programming, but it is also incredibly limited (you only have 32KB). Luckily for us, there are structures that we can move from IWRAM to EWRAM without affecting the gameplay--this will allow us to make room for our new mixer.

We will be moving two structs that store data related to the RFU--that is, the Wireless Adapter. These two structs are gRfu and gRfuAPIBuffer, both located in src/link_rfu_2.c. If you head to that file, you will see these two lines starting at line 80:

u32 gRfuAPIBuffer[RFU_API_BUFF_SIZE_RAM / 4];
struct RfuManager gRfu;

To move these to EWRAM, change these two lines to:

EWRAM_DATA u32 gRfuAPIBuffer[RFU_API_BUFF_SIZE_RAM / 4] = {};
EWRAM_DATA struct RfuManager gRfu = {};

Next, we need to go to librfu_rfu to make a small code change to allow the Wireless Adapter to function with these structs in EWRAM. Scrolling down to line 134 will reveal there is actually a check to see if the structs are in EWRAM, and if the check returns true, it will send an error and not allow the usage of the Wireless Adapter. I have confirmed that this works on console, so I am not sure what the purpose of this check is, but all we need to do is comment out or delete the two lines:

-if (((uintptr_t)APIBuffer & 0xF000000) == 0x2000000 && copyInterruptToRam)
-    return ERR_RFU_API_BUFF_ADR;

Next, go to sym_common.txt and delete the line that says .include "link_rfu_2.o" on line 37:

    .include "AgbRfu_LinkManager.o"
-   .include "link_rfu_2.o"
    .include "rtc.o"

Finally, delete the file common_syms/link_rfu_2.txt.

Now we are done--the ROM can finally be built and should work with the new mixer. But there are more things we can do.

Making More Room in RAM (Optional)

The changes we have made leave enough room in RAM for the mixer to work with no problems at the default engine rate. However, if you increase the engine rate, and thus increase the size of our new hq_buffer_ptr array, you may still run into memory issues. Luckily, there is one more thing we can do.

The Pokemon games use 5 DirectSound channels, but m4a always allocates space for the maximum amount, 12. This is wasteful; we can reclaim some free memory from this. Note that if you have edited the number of DirectSound channels in m4a.c to be larger than 5, you will want to use that value instead of 5 in the following replacements.

In constants/m4a_constants.inc, change MAX_DIRECTSOUND_CHANNELS from 12 to 5. Next, in include/gba/m4a_internal.h, change the same MAX_DIRECTSOUND_CHANNELS define from 12 to 5 again. Now we have reclaimed all of the memory we can, and the mixer can go to higher rates without overflowing memory.

Changing the PCM Buffer Size (for Accurate Reverb)

Note that this section only applies if you have both increased the engine rate in m4a.c and have not disabled reverb. By default, the size of the PCM DMA buffer is enough to hold 7 frames of audio, which is how many frames the reverb algorithm expects to be there. If you increase the engine rate without increasing the PCM buffer size, the game will not crash or anything, but you will notice that the reverb sounds shorter, and depending on how high you set the engine rate, almost nonexistent. The fix for this is increasing the PCM buffer size to be able to hold 7 frames of audio in our new engine rate. You will notice that by default the buffer size is 1584; this value comes from the frame size (see the list in the Replacing the Mixer Code section) multiplied by 7, with 0x10 added for safety (this is unnecessary and we will not be doing it for our new sizes). Thus we can calculate the PCM buffer size that we need for every possible engine frequency:

5734Hz: 672
7884Hz: 924 (This mode is not aligned to the buffer length and is not supported by the mixer)
10512Hz: 1232
13379Hz: 1568 (As mentioned, the actual value used by the default mixer adds 16 to this)
15768Hz: 1848
18157Hz: 2128
21024Hz: 2464
26758Hz: 3136
31536Hz: 3696
36314Hz: 4256
40137Hz: 4704
42048Hz: 4928

Now all that we need to do is replace the definitions of the buffers. This must be done in the following two locations:

  1. In constants/m4a_constants.inc, PCM_DMA_BUF_SIZE is set on line 3; change it there.
  2. In include/gba/m4a_internal.h, PCM_DMA_BUF_SIZE is set on line 169; change it there.

Making DMA transfers atomic

Because the new sound engine uses DMA3 (by default, see Mixer Config below), which the game does not expect, we have to make some adjustments to prevent game crashes. The reason we have to do this is that pokeemerald writes the DMA registers value by value which leaves a very small chance for interrupts inbetween those register writes. If we interrupt those writes before the DMA transfer is enabled (which is done by the last write) we will corrupt the register state and once the interrupt returns, a DMA transfer is initiated with the wrong values.

We can fix this very easily by using the STMIA instruction for DMA register writes, which cannot be interrupted. If we do that we can make sure the registers are always in a well defined state. Either a transfer is initialized and completed or it is has not begun yet. See the following patch which makes the game write to DMA by using STMIA in include/gba/macro.h:

 #define DmaSet(dmaNum, src, dest, control)        \
 {                                                 \
     vu32 *dmaRegs = (vu32 *)REG_ADDR_DMA##dmaNum; \
-    dmaRegs[0] = (vu32)(src);                     \
-    dmaRegs[1] = (vu32)(dest);                    \
-    dmaRegs[2] = (vu32)(control);                 \
-    dmaRegs[2];                                   \
+    u32 eval_src = (u32)(src);                    \
+    u32 eval_dst = (u32)(dest);                   \
+    u32 eval_ctl = (u32)(control);                \
+    register u32 r_src asm("r0") = eval_src;      \
+    register u32 r_dst asm("r1") = eval_dst;      \
+    register u32 r_ctl asm("r2") = eval_ctl;      \
+    asm volatile("stmia %0!, {%1, %2, %3}" : "+l" (dmaRegs) : "l" (r_src), "l" (r_dst), "l" (r_ctl) : "memory");  \
 }

Mixer Config

Lastly, I would like to briefly explain the two options at the top of the mixer code, namely ENABLE_REVERB and ENABLE_DMA.

ENABLE_REVERB does exactly what it sounds like; if set to 1, reverb will be applied as normal, sounding just like the original game. If set to 0, all reverb processing will be skipped, and the game will have no reverb. This is completely up to personal choice, but if you just want it to sound like the original game, leave it on.

ENABLE_DMA, when set to 1, has the code use DMA3 for transferring data rather than doing a standard CPU copy. This results in faster and smaller code, but it can lead to the DMA being used for so long that it halts the CPU for an extra hblank cycle. This almost certainly will not affect you, and the results are not noticeable. If you do not know what exactly this means, just leave it on as-is. However, if you know that your use case does not allow DMA, you can set this to 0 to make the mixer do a CPU copy instead; note that this will make the code slightly larger (the code buffer size is set up for the worst-case scenario, so do not worry about that) and slightly slower (but the speed difference should not be noticeable).

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