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Merged
vk2seb merged 1 commit into from
Apr 12, 2026
Merged

top/xbeam/persist: unify decay/persist, reduce flickering #165

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37 changes: 32 additions & 5 deletions gateware/src/rs/hal/src/persist.rs
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Original file line number Diff line number Diff line change
@@ -1,6 +1,11 @@
/// Unified persistence control.
///
/// Maps a single 1-80 value to decay, holdoff and probabilistic skip:
/// 1-15: decay ramps 15->1, holdoff=32, skip=0
/// 16-64: decay=1, holdoff=32, skip ramps up
/// 65-80: decay=1, holdoff ramps 32->256, skip continues ramping
pub trait Persist {
fn set_persist(&mut self, value: u16);
fn set_decay(&mut self, value: u8);
fn set_persistence(&mut self, value: u8);
}

#[macro_export]
Expand All @@ -18,17 +23,39 @@ macro_rules! impl_persist {
pub fn new(registers: $PACPERSISTX) -> Self {
Self { registers }
}
}

impl hal::persist::Persist for $PERSISTX {
fn set_persist(&mut self, value: u16) {
fn set_holdoff(&mut self, value: u16) {
self.registers.persist().write(|w| unsafe { w.persist().bits(value) } );
}

fn set_decay(&mut self, value: u8) {
self.registers.decay().write(|w| unsafe { w.decay().bits(value) } );
}

fn set_skip(&mut self, value: u8) {
self.registers.skip().write(|w| unsafe { w.skip().bits(value) } );
}
}

impl hal::persist::Persist for $PERSISTX {
fn set_persistence(&mut self, value: u8) {
let p = value as u32;
if p <= 15 {
self.set_decay((16 - p) as u8);
self.set_holdoff(32);
self.set_skip(0);
} else {
let t = p - 16; // 0..64
self.set_decay(1);
self.set_skip(core::cmp::min(t << 2, 255) as u8);
if p <= 64 {
self.set_holdoff(32);
} else {
let h = p - 65; // 0..15
self.set_holdoff(core::cmp::min(32 + (h << 5), 256) as u16);
}
}
}
}
)+
};
Expand Down
30 changes: 27 additions & 3 deletions gateware/src/tiliqua/raster/persist.py
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,7 @@ def __init__(self, *, bus_signature,
# Tweakables
"holdoff": In(16, init=holdoff_default),
"decay": In(4, init=1),
"skip": In(8, init=0),
# DMA bus / fb
"bus": Out(bus_signature),
"fbp": In(DMAFramebuffer.Properties()),
Expand Down Expand Up @@ -70,11 +71,21 @@ def elaborate(self, platform) -> Module:

# Latched version of decay speed control input
decay_latch = Signal.like(self.decay)
# Latched version of skip probability control input
skip_latch = Signal.like(self.skip)
# Track delay between read/write bursts
holdoff_count = Signal(32)
# Incoming pixel array (read from FIFO)
pixels_r = Signal(data.ArrayLayout(Pixel, 4))

# Free-running LFSR for probabilistic pixel skipping.
lfsr0 = Signal(unsigned(32), init=0x67452301)
lfsr1 = Signal(unsigned(32), init=0xefcdab89)
lfsr1_next = Signal(unsigned(32))
m.d.comb += lfsr1_next.eq(lfsr1 + lfsr0)
m.d.sync += lfsr1.eq(lfsr1_next)
m.d.sync += lfsr0.eq(lfsr0 ^ lfsr1_next)

m.d.comb += self.fifo.w_data.eq(bus.dat_r)

# Used for fastpath when all pixels are zero
Expand All @@ -101,6 +112,7 @@ def elaborate(self, platform) -> Module:

with m.State('BURST-IN'):
m.d.sync += decay_latch.eq(self.decay)
m.d.sync += skip_latch.eq(self.skip)
m.d.comb += [
bus.stb.eq(1),
bus.cyc.eq(1),
Expand Down Expand Up @@ -135,12 +147,17 @@ def elaborate(self, platform) -> Module:

with m.State('BURST-OUT'):
# The actual persistance calculation. 4 pixels at a time.
#
# Per-pixel LFSR comparison decides whether to decay or
# write back unchanged (probabilistic skip).
pixels_w = Signal(data.ArrayLayout(Pixel, 4))
for n in range(4):
# color
skip_this = Signal(name=f"skip_{n}")
m.d.comb += skip_this.eq(lfsr1[n*8:(n*8)+8] < skip_latch)
m.d.comb += pixels_w[n].color.eq(pixels_r[n].color)
# intensity
with m.If(pixels_r[n].intensity >= decay_latch):
with m.If(skip_this):
m.d.comb += pixels_w[n].intensity.eq(pixels_r[n].intensity)
with m.Elif(pixels_r[n].intensity >= decay_latch):
m.d.comb += pixels_w[n].intensity.eq(pixels_r[n].intensity - decay_latch)
with m.Else():
m.d.comb += pixels_w[n].intensity.eq(0)
Expand Down Expand Up @@ -184,6 +201,9 @@ class PersistReg(csr.Register, access="w"):
class DecayReg(csr.Register, access="w"):
decay: csr.Field(csr.action.W, unsigned(8))

class SkipReg(csr.Register, access="w"):
skip: csr.Field(csr.action.W, unsigned(8))

def __init__(self, bus_dma):
self.en = Signal()
self.persist = Persistance(bus_signature=bus_dma.bus.signature.flip())
Expand All @@ -193,6 +213,7 @@ def __init__(self, bus_dma):

self._persist = regs.add("persist", self.PersistReg(), offset=0x0)
self._decay = regs.add("decay", self.DecayReg(), offset=0x4)
self._skip = regs.add("skip", self.SkipReg(), offset=0x8)

self._bridge = csr.Bridge(regs.as_memory_map())

Expand All @@ -216,4 +237,7 @@ def elaborate(self, platform):
with m.If(self._decay.f.decay.w_stb):
m.d.sync += self.persist.decay.eq(self._decay.f.decay.w_data)

with m.If(self._skip.f.skip.w_stb):
m.d.sync += self.persist.skip.eq(self._skip.f.skip.w_data)

return m
2 changes: 1 addition & 1 deletion gateware/src/top/bootloader/fw/src/main.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -849,7 +849,7 @@ fn main() -> ! {
let mut logo_coord_ix = 0u32;
let mut rng = fastrand::Rng::with_seed(0);

persist.set_persist(256);
persist.set_persistence(64);

let stroke = PrimitiveStyleBuilder::new()
.stroke_color(HI8::new(0, 10))
Expand Down
6 changes: 2 additions & 4 deletions gateware/src/top/macro_osc/fw/src/main.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -360,11 +360,9 @@ fn main() -> ! {
}

if on_help_page {
persist.set_persist(256);
persist.set_decay(1);
persist.set_persistence(64);
} else {
persist.set_persist(opts.beam.persist.value);
persist.set_decay(opts.beam.decay.value);
persist.set_persistence(opts.beam.persist.value);
}

vscope.set_hue(opts.beam.hue.value);
Expand Down
7 changes: 2 additions & 5 deletions gateware/src/top/macro_osc/fw/src/options.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -63,8 +63,7 @@ int_params!(NoteParams<u8> { step: 1, min: 0, max: 128 });
int_params!(HarmonicsParams<u8> { step: 8, min: 0, max: 240 });
int_params!(TimbreParams<u8> { step: 8, min: 0, max: 240 });
int_params!(MorphParams<u8> { step: 8, min: 0, max: 240 });
int_params!(PersistParams<u16> { step: 128, min: 128, max: 8192 });
int_params!(DecayParams<u8> { step: 1, min: 0, max: 15 });
int_params!(PersistParams<u8> { step: 1, min: 1, max: 80 });
int_params!(IntensityParams<u8> { step: 1, min: 0, max: 15 });
int_params!(HueParams<u8> { step: 1, min: 0, max: 15 });
int_params!(TriggerLvlParams<i16> { step: 500, min: -16000, max: 16000, format: IntFormat::Scaled { divisor: 4000, precision: 2, suffix: "V" } });
Expand Down Expand Up @@ -113,10 +112,8 @@ pub struct VectorOpts {

#[derive(OptionPage, Clone)]
pub struct BeamOpts {
#[option(256)]
#[option(15)]
pub persist: IntOption<PersistParams>,
#[option(1)]
pub decay: IntOption<DecayParams>,
#[option(8)]
pub intensity: IntOption<IntensityParams>,
#[option(10)]
Expand Down
9 changes: 3 additions & 6 deletions gateware/src/top/polysyn/fw/src/main.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -217,10 +217,9 @@ fn build_cc_mapper(opts: &Opts) -> MidiCcMapper {
// Effect page (CC 40-41)
m.add(40, global_index(opts, &opts.effect.drive), CcMapMode::Absolute);
m.add(41, global_index(opts, &opts.effect.diffuse), CcMapMode::Absolute);
// Beam page (CC 50-55)
// Beam page (CC 50-55, CC 52 formerly decay now unused)
m.add(50, global_index(opts, &opts.beam.scale), CcMapMode::Absolute);
m.add(51, global_index(opts, &opts.beam.persist), CcMapMode::Absolute);
m.add(52, global_index(opts, &opts.beam.decay), CcMapMode::Absolute);
m.add(53, global_index(opts, &opts.beam.intensity), CcMapMode::Absolute);
m.add(54, global_index(opts, &opts.beam.hue), CcMapMode::Absolute);
m.add(55, global_index(opts, &opts.beam.palette), CcMapMode::Absolute);
Expand Down Expand Up @@ -484,12 +483,10 @@ fn main() -> ! {
v_active,
opts.help.scroll.value,
opts.beam.hue.value).ok();
persist.set_persist(128);
persist.set_decay(1);
persist.set_persistence(64);
vscope.set_enabled(false);
} else {
persist.set_persist(opts.beam.persist.value);
persist.set_decay(opts.beam.decay.value);
persist.set_persistence(opts.beam.persist.value);
vscope.set_enabled(true);
}

Expand Down
7 changes: 2 additions & 5 deletions gateware/src/top/polysyn/fw/src/options.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -83,8 +83,7 @@ int_params!(ResoParams<u16> { step: 2048, min: 0, max: 32768, format: IntF
int_params!(DiffuseParams<u16> { step: 2048, min: 0, max: 32768, format: IntFormat::Scaled { divisor: 32768, precision: 2, suffix: "" } });
int_params!(AdsrTimeParams<u16> { step: 1024, min: 0, max: 16384, format: IntFormat::Scaled { divisor: 16384, precision: 2, suffix: "" } });
int_params!(AdsrLevelParams<u16> { step: 1024, min: 0, max: 32768, format: IntFormat::Scaled { divisor: 32768, precision: 2, suffix: "" } });
int_params!(PersistParams<u16> { step: 32, min: 32, max: 4096 });
int_params!(DecayParams<u8> { step: 1, min: 0, max: 15 });
int_params!(PersistParams<u8> { step: 1, min: 1, max: 80 });
int_params!(IntensityParams<u8> { step: 1, min: 0, max: 15 });
int_params!(HueParams<u8> { step: 1, min: 0, max: 15 });
int_params!(ScrollParams<u8> { step: 1, min: 0, max: 125 });
Expand Down Expand Up @@ -139,10 +138,8 @@ pub struct AdsrOpts {
pub struct BeamOpts {
#[option(VScale::Scale2V)]
pub scale: EnumOption<VScale>,
#[option(32)]
#[option(15)]
pub persist: IntOption<PersistParams>,
#[option(1)]
pub decay: IntOption<DecayParams>,
#[option(8)]
pub intensity: IntOption<IntensityParams>,
#[option(10)]
Expand Down
4 changes: 2 additions & 2 deletions gateware/src/top/polysyn/top.py
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Original file line number Diff line number Diff line change
Expand Up @@ -106,8 +106,8 @@
EFFECT diffuse 41 diffusion wet/dry mix

BEAM scale 50 vectorscope volts/div
BEAM persist 51 phosphor decay speed (high = slow)
BEAM decay 52 phosphor decay amount (low = slow)
BEAM persist 51 phosphor persistence (high = slow)
- (CC 52 deprecated)
BEAM intensity 53 trace intensity
BEAM hue 54 trace and menu hue
BEAM palette 55 color palette
Expand Down
6 changes: 2 additions & 4 deletions gateware/src/top/sampler/fw/src/main.rs
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Expand Up @@ -312,11 +312,9 @@ fn main() -> ! {
v_active,
opts.help.scroll.value,
hue).ok();
persist.set_persist(128);
persist.set_decay(1);
persist.set_persistence(64);
} else {
persist.set_persist(128);
persist.set_decay(1);
persist.set_persistence(32);
}


Expand Down
2 changes: 1 addition & 1 deletion gateware/src/top/selftest/fw/src/main.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -480,7 +480,7 @@ fn main() -> ! {
irq::scope(|s| {

palette::ColorPalette::default().write_to_hardware(&mut display);
persist.set_persist(128);
persist.set_persistence(20);

s.register(handlers::Interrupt::TIMER0, timer0);

Expand Down
4 changes: 2 additions & 2 deletions gateware/src/top/sid/fw/src/main.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -272,7 +272,7 @@ fn main() -> ! {

// Draw UI elements
if on_help_page {
persist.set_persist(128);
persist.set_persistence(64);
draw::draw_options(&mut display, &opts, h_active/2-30, v_active-100, hue).ok();
draw::draw_name(&mut display, h_active/2, v_active-50, hue,
&bootinfo.manifest.name, &bootinfo.manifest.tag, &modeline).ok();
Expand All @@ -284,7 +284,7 @@ fn main() -> ! {
opts.help.scroll.value,
hue).ok();
} else {
persist.set_persist(64);
persist.set_persistence(15);
draw::draw_options(&mut display, &opts, 100, v_active/2, hue).ok();
draw::draw_name(&mut display, h_active/2, v_active-50, hue,
&bootinfo.manifest.name, &bootinfo.manifest.tag, &modeline).ok();
Expand Down
9 changes: 3 additions & 6 deletions gateware/src/top/xbeam/fw/src/main.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -60,9 +60,8 @@ fn build_cc_mapper(opts: &Opts) -> MidiCcMapper {
m.add(31, global_index(opts, &opts.delay.delay_y), CcMapMode::Absolute);
m.add(32, global_index(opts, &opts.delay.delay_i), CcMapMode::Absolute);
m.add(33, global_index(opts, &opts.delay.delay_c), CcMapMode::Absolute);
// Beam page (CC 40-45)
// Beam page (CC 40-45, CC 41 formerly decay now unused)
m.add(40, global_index(opts, &opts.beam.persist), CcMapMode::Absolute);
m.add(41, global_index(opts, &opts.beam.decay), CcMapMode::Absolute);
m.add(42, global_index(opts, &opts.beam.ui_hue), CcMapMode::Absolute);
m.add(43, global_index(opts, &opts.beam.palette), CcMapMode::Absolute);
m.add(44, global_index(opts, &opts.beam.grid), CcMapMode::Absolute);
Expand Down Expand Up @@ -281,11 +280,9 @@ fn main() -> ! {
v_active,
opts.help.scroll.value,
opts.beam.ui_hue.value).ok();
persist.set_persist(128);
persist.set_decay(1);
persist.set_persistence(64);
} else {
persist.set_persist(opts.beam.persist.value);
persist.set_decay(opts.beam.decay.value);
persist.set_persistence(opts.beam.persist.value);
}


Expand Down
7 changes: 2 additions & 5 deletions gateware/src/top/xbeam/fw/src/options.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -90,8 +90,7 @@ pub enum XZoom {

int_params!(DelayParams<u16> { step: 8, min: 0, max: 512, format: IntFormat::Scaled { divisor: AUDIO_FS / 1000, precision: 1, suffix: "ms" } });
int_params!(PCScaleParams<u8> { step: 1, min: 0, max: 15 });
int_params!(PersistParams<u16> { step: 32, min: 32, max: 4096 });
int_params!(DecayParams<u8> { step: 1, min: 0, max: 15 });
int_params!(PersistParams<u8> { step: 1, min: 1, max: 80 });
int_params!(IntensityParams<u8> { step: 1, min: 0, max: 15 });
int_params!(HueParams<u8> { step: 1, min: 0, max: 15 });
int_params!(TriggerLvlParams<i16> { step: 500, min: -16000, max: 16000, format: IntFormat::Scaled { divisor: 4000, precision: 2, suffix: "V" } });
Expand Down Expand Up @@ -141,10 +140,8 @@ pub struct DelayOpts {

#[derive(OptionPage, Clone)]
pub struct BeamOpts {
#[option(32)]
#[option(15)]
pub persist: IntOption<PersistParams>,
#[option(1)]
pub decay: IntOption<DecayParams>,
#[option(10)]
pub ui_hue: IntOption<HueParams>,
#[option]
Expand Down
4 changes: 2 additions & 2 deletions gateware/src/top/xbeam/top.py
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Original file line number Diff line number Diff line change
Expand Up @@ -104,8 +104,8 @@
DELAY delay-i 32 in2/intensity delayline length
DELAY delay-c 33 in3/color delayline length

BEAM persist 40 phosphor decay speed (high = slow)
BEAM decay 41 phosphor decay amount (low = slow)
BEAM persist 40 phosphor persistence (high = slow)
- (CC 41 deprecated)
BEAM ui-hue 42 menu and grid overlay hue
BEAM palette 43 color palette
BEAM grid 44 grid overlay style
Expand Down
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