PSG
Channels
Pulse
Ramp
Noise
The noise channel doesn’t have a pulse width
Envelope
Tip
By default, the envelope does nothing. You can safely ignore it, if you don’t want to use it.
Each channel has an envelope generator. This allows automated control for some parameters, such as volume and pitch. It has two memory mapped registers: mask, and length. Mask is a bitmask for envelope settings, and length controls the length of the envelope.
Envelope Mask
| Flag name | Bit | Description |
|---|---|---|
| FLAG_VOL | 0 | Controls Volume (Manual volume control still applies over this). |
| FLAG_PW | 1 | Controls Pulse Width / Duty Cycle (Overrides manual control). |
| FLAG_FREQ | 2 | Controls Pitch (sweep effect). |
| FLAG_GATE | 3 | Enable Gate: Mute when timer runs out. Independent from volume flag. |
| FLAG_FALLING | 4 | Falling instead of rising: Envelope goes from 100% to 0% instead of 0% to 100%. |
| 5 | unused | |
| FLAG_LOOP | 6 | Envelope loops. Envelope starts over if it runs out. |
| FLAG_LOOP_MIRROR | 7 | If looping, every other cycle is reversed (rise-fall-rise-fall…). |
Default value for mask is 0, meaning that no bits are set.
Memory Map
| Addr | Global | Access | Name | Description |
|---|---|---|---|---|
| 0x00 | todo | W | ch0_freq | Pulse 0 Frequency in Hz |
| 0x01 | 0x01 | W | ch0_vol | Pulse 0 Volume |
| 0x02 | 0x02 | W | ch0_pw | Pulse 0 Pulse width |
| 0x03 | 0x03 | W | ch0_env_mask | Pulse 0 Envelope mask |
| 0x04 | 0x04 | W | ch0_env_length | Pulse 0 Envelope length in milliseconds |
| … | ||||
| 0x10 | 0x10 | W | ch1_freq | Pulse 1 Frequency in Hz |
| 0x11 | 0x11 | W | ch1_vol | Pulse 1 Volume |
| 0x12 | 0x12 | W | ch1_pw | Pulse 1 Pulse width |
| 0x13 | 0x13 | W | ch1_env_mask | Pulse 1 Envelope mask |
| 0x14 | 0x14 | W | ch1_env_length | Pulse 1 Envelope length in milliseconds |
| … | ||||
| 0x20 | 0x20 | W | ch2_freq | Ramp Frequency in Hz |
| 0x21 | 0x21 | W | ch2_vol | Ramp Volume |
| 0x22 | 0x22 | W | ch2_dc | Ramp Duty cycle |
| 0x23 | 0x23 | W | ch2_env_mask | Ramp Envelope mask |
| 0x24 | 0x24 | W | ch2_env_length | Ramp Envelope length in milliseconds |
| … | ||||
| 0x30 | 0x30 | W | ch3_freq | Noise Frequency in Hz |
| 0x31 | 0x31 | W | ch3_vol | Noise Volume |
| 0x33 | 0x33 | W | ch3_env_mask | Noise Envelope mask |
| 0x34 | 0x34 | W | ch3_env_length | Noise Envelope length in milliseconds |
Examples
Todo