USB MIDI support

[djdiskmachine]

I've been attempting to add support for usb midi for LittleGPTracker (github.com/djdiskmachine/littlegptracker) like it has on raspberry pi and other platforms.
I used the cfw buildroot repo to build the .s0 files that were missing in the toolchain and enabled the rtmidi modules for Bittboy(fw 2.0.0 Beta 2 ). LGPT starts with these messages in the log.

[ERROR] Couldn't get RtMidiIn object
[ERROR] RtMidiIn::initialize: error creating ALSA sequencer input client objec
t.
[ERROR] Couldn't get RtMidiOut object
[ERROR] RtMidiOut::initialize: error creating ALSA sequencer client object.

This is after ld_preload of rtmidi.s0 before starting lgot.

Not sure how to progress from here, any suggestions?

[TriForceX]

are you using the same cfw generated from your modified buildroot?

[djdiskmachine]

I am not, I wasn't sure how to generate an image from it.

[djdiskmachine]

I realized I've bee using a deprecated toolchain:
https://github.com/MiyooCFW/toolchain

I'll adjust to the current one and report back

[Apaczer]

To have MIDI gadget at your disposal, you have to enable specific kernel modules, thus in MiyooCFW/kernel:

diff --git a/arch/arm/configs/miyoo_defconfig b/arch/arm/configs/miyoo_defconfig
index 56fdf7362..d1bdeae7f 100644
--- a/arch/arm/configs/miyoo_defconfig
+++ b/arch/arm/configs/miyoo_defconfig
@@ -80,6 +80,7 @@ CONFIG_FRAMEBUFFER_CONSOLE_DETECT_PRIMARY=y
 CONFIG_SOUND=y
 CONFIG_SND=y
 # CONFIG_SND_VERBOSE_PROCFS is not set
+CONFIG_SND_SEQUENCER=m
 CONFIG_SND_ALOOP=m
 # CONFIG_SND_ARM is not set
 CONFIG_SND_SOC=y
@@ -95,6 +96,7 @@ CONFIG_USB_CONFIGFS=y
 CONFIG_USB_CONFIGFS_F_HID=y
 CONFIG_USB_FUNCTIONFS=m
 CONFIG_USB_G_SERIAL=m
+CONFIG_USB_MIDI_GADGET=m
 CONFIG_USB_G_HID=m
 CONFIG_MMC=y
 CONFIG_MMC_SUNXI=y

Then you can look for snd-seq*.ko output files in sound/core/ and load to your handheld via insmod cmd (the same probably goes for g_midi gadget from drivers/usb/gadget/legacy/ output directory). If you tell your buildroot configurtion to point to your custom kernel setup, you could then just load the drivers with simple modprobe after generating CFW *.img

This have not been tested I believe for F1C100S, so you may lower your expectactions as there is little support for this SOC in sunxi community.

[djdiskmachine]

Thank you I'll try that, why are these flagged with m rather than y?

[djdiskmachine]

Good news: I got a bootable image
Bad news: still not quite there, applying the ko files produced this output

insmod snd-seq.ko
insmod: can't insert 'snd-seq.ko': unknown symbol in module, or unknown parameter
modinfo
dmesg | tail -n 20
.......
[ 184.731358] musb_g_ep0_irq 686: SetupEnd came in a wrong ep0stage out/status
[ 395.889643] snd_seq_midi_event: Unknown symbol snd_seq_expand_var_event (err -2)
[ 395.891201] snd_seq_midi_event: Unknown symbol snd_seq_expand_var_event (err -2)
[ 442.588510] snd_seq: Unknown symbol snd_seq_autoload_init (err -2)
[ 442.588942] snd_seq: Unknown symbol snd_seq_autoload_exit (err -2)
[ 442.589098] snd_seq: Unknown symbol snd_seq_device_load_drivers (err -2)
[ 442.596291] snd_seq: Unknown symbol snd_seq_autoload_init (err -2)
[ 442.596723] snd_seq: Unknown symbol snd_seq_autoload_exit (err -2)
[ 442.596879] snd_seq: Unknown symbol snd_seq_device_load_drivers (err -2)

[Apaczer]

Looking at modules.order output u should insmod/modprobe in following manner:

snd-seq-device.ko
snd-rawmidi.ko
snd-seq.ko
snd-seq-midi-event.ko (this one was out of order strangely)
snd-seq-midi.ko

You say M for module, and Y for builtin and loaded to memory from kernel img by bootloader

[djdiskmachine]

That does indeed appear to be the right order. I no longer see the the unable to create alsa client errors but there doesn't seem to be any midi devices anyway. I tried calling modprobe g_midi and modprobe g_midi index=1 before running lgpt but no success