Differences

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--- audio_controller [2025/03/20 20:54] – arisotura
+++ audio_controller [2025/03/21 22:16] (current) – arisotura
@@ Line 1: / Line 1: @@
 ====== Audio controller ======
-The gamepad has a simple audio controller that presumably just streams raw PCM16 to the speakers/headphone jack.
+The audio controller has two main components: output (playing sound to the internal speakers or headphone jack) and input (recording sound from the internal microphone). It supports PCM16 and A-law or µ-law encoded PCM8. Sound output can be mono or stereo, input is always mono.
+Sample frequencies of 48 KHz and 24 KHz are supported. Supporting different frequencies would require reconfiguring the [[audio amplifier]], which is responsible for generating the audio sample/bit clocks.
 Register map:
@@ Line 41: / Line 43: @@
 | 0x17 | Audio output event |
 | 0x18 | Audio input event |
-| 0x1E | Periodic IRQ |
-IRQ 0x17 is used to signal certain events related to audio playback, such as start or end of playback.
-IRQ 0x1E is used by the stock firmware for certain non-audio tasks such as input polling. It seems to always trigger periodically no matter what. I measured the period to be ~5547 microseconds (~600000 cycles), no idea what this represents.
-Not yet known:
-  * if it is possible to play a looping sound (TODO check F0005420 bit0)
-  * how to set the sample rate (prolly directly on the amplifier)
@@ Line 86: / Line 77: @@
 Sound data is transmitted to the amplifier over an I2S interface. The sample clock and bit clock are generated by the amplifier, at speeds of 48 KHz and 3.08 MHz respectively.
-Bits 6-10 control when a sample starts relative to the sample clock edges. The default setting is 1. This setting should match the audio amplifier's data offset setting (page 0 register 28).
+Bits 6-10 control when a sample starts relative to the sample clock edges. The default setting is 1. This setting should match the audio amplifier's data offset setting (page 0 register 28; default setting of 0 means an offset of 1 cycle).
 Bits 11-15 seem to control the bit width of samples. 0 seems to be interpreted as 32. In practice, values 16 and above act the same. The default setting is 0.
@@ Line 124: / Line 115: @@
 Bits 3-27 are writable. It seems that the playback address has a resolution of 16 bytes (atleast with settings: 48KHz stereo 16bit), ie. setting bit 3 will cause the buffer to be played repeatedly.
-Writing to this register while playback is in progress has no effect. TODO: not yet known how to cleanly stop playback.
+Writing to this register while playback is in progress has no effect.