Mega Blaster 2 Firmware

This firmware update fixes two things:

• The PSG frequency register now updates when only the low-byte is written to. This is uncommon on VGM files for "real" genesis games, but occasionally occurs on some homebrew tracks, causing the PSG to sound out-of-tune or flat out incorrect. Thank you to @natarii for solving that issue and graciously sharing your solution.
• FM channel muting has been fixed. Previous versions were targeting incorrect key-on registers.

Mega Blaster 2 Firmware

• Added a new sync-tone feature.
  For users looking to sync-up individual channel audio streams in their external recording software, this update adds a "Sync-tone" feature that may give you a helping hand.

When the sync-tone feature is enabled, every unmuted FM and PSG channel will emit three tones on and off, 250ms between each key on/off. Then, 250ms later, the track will start. The YM2612/3438 use FM Channel 6 for PCM samples sent to the DAC, therefore, you can sync the PCM track using Channel 6.

This update is handy for syncing up oscilloscope videos. You can mute all but one sound chip channel at a time, record your 'scope video, then do the same for each channel. The sync-tone will help you find the starting point of each stream, even if a particular channel is muted at the start of a soundtrack.

Pro tip: The PSG's 3rd square-wave channel and noise channel will interact with one another if they are both un-muted at the same time. If both channels are active when the sync-tone is played, the PSG may sound detuned or inconsistent. It's recommended to only have either the 3rd square wave channel OR the noise channel un-muted at a time.

Mega Blaster 2 Firmware

• Fixed DAC stream playback

Mega Blaster 2 Firmware

• Fixes shuffle RNG.

Music player used to select the same sequence of songs every time. This patch correctly calls the built-in true random number generator (TRNG) on the microcontroller to generate new random sequences of songs on every boot.

Mega Blaster 2 Firmware

New Feature: Individual channel muting for both FM and PSG courtesy of @renedare

You can toggle each FM and PSG channel individually by going to the new "Channel Control" menu by scrolling down the Main Menu.
There, you can toggle each individual channel "ON" and "OFF."

If you've ever wanted to deconstruct a Genesis soundtrack into it's constitute instruments, this update is for you!

This feature is experimental, but works quite well already.

DAC streams and PCM samples are played out of FM Channel 6.

Mega Blaster 2 Firmware

OPTIONAL
This firmware allows for SI5351(A) variant clock generators to be used. This new firmware will detect if your unit is using a SI5351 or SI5351A clock generator and will configure it automatically. These devices are functionally identical but have different I2C addresses. There's no difference in performance between these two parts.

This change was made to allow for component choice flexibility given the current electronics component shortage occurring as of mid-2021.

Mega Blaster 2 Firmware

Fixed the following bugs:

• Folders with a large number of files incorrectly reported their index, causing strange out-of-order issues while in the "IN_ORDER" playback mode.

• "SHUFFLE_ALL" and "SHUFFLE_DIR" playback modes had a couple of issues regarding file indexing as well, causing the player to overflow it's random file history list and subsequently pick invalid file indexes when traversing through the random track history.

• Random track history has been extended to 20 tracks; up from 5.

Mega Blaster 2 Firmware

Prevent writing to the OPN2 test registers (0x21 and 0x2C)
Some broken VGM files will write to these registers and cause huge distortion issues. This is technically an illegal operation and by blocking these writes, a few common broken VGM packs now function correctly, such as:

• Rocket Knight Adventures
• Comix Zone (also has some minor messed up PCM stuff, but that's in the domain of the VGM author, not my player)

Mega Blaster 2 Firmware

This new patch fixes a bug that prevented sequential folders beginning with the same substring from being opened correctly. Thanks to Bill over at the SdFat project for the help!

Mega Blaster 2 Firmware

The manifest system has been removed in favor of a dynamic system at the expense of a bit more compute time and RAM usage.
The manifest system was fairly slow and unreliable, especially when the SD card was filled with lots of files.

You will no longer have to wait at startup for the manifest to build or verify itself.

I've also put in a check for useless meta folders like System Volume Information and .DS_Store
If these are found on the root directory, the are removed on boot. If these meta files are found after entering a directory, they will be removed after selecting a track. These may still show up in your file menu temporarily, but should go away after a refresh and never appear again unless the SD card is re-written to.