adafruit-mirror/Adafruit_Blinka_Raspberry_Pi5_Piomatter
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Reduce PIO clock speed, remove CLOCKS_PER_DATA workaround

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we now understand why the fudge factor was needed to achieve a
plausible brightness ramp.
This commit is contained in:
Jeff Epler 2025-01-24 10:23:55 -06:00
parent 8fb5ba4339
commit a532a9105e
2 changed files with 9 additions and 4 deletions
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9
src/include/piomatter/piomatter.h
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@ -114,7 +114,14 @@ struct piomatter : piomatter_base {
sm_config_set_out_shift(&c, /* shift_right= */ false,
/* auto_pull = */ true, 32);
sm_config_set_fifo_join(&c, PIO_FIFO_JOIN_TX);
sm_config_set_clkdiv(&c, 1.0);
// Due to https://github.com/raspberrypi/utils/issues/116 it's not
// possible to keep the RP1 state machine fed at high rates. This target
// frequency is approximately the best sustainable clock with current
// FW & kernel.
constexpr double target_freq =
2700000; // 2.7MHz PIO clock -> 1.35MHz pixel clock
double div = clock_get_hz(clk_sys) / target_freq;
sm_config_set_clkdiv(&c, div);
sm_config_set_out_pins(&c, 0, 28);
pio_sm_init(pio, sm, offset, &c);
pio_sm_set_enabled(pio, sm, true);

4
src/include/piomatter/render.h
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@ -8,9 +8,7 @@
namespace piomatter {
constexpr unsigned DATA_OVERHEAD = 3;
// this is ... flatly wrong!? but it's the number that makes the ramp intensity
// correct to my eye
constexpr unsigned CLOCKS_PER_DATA = 128;
constexpr unsigned CLOCKS_PER_DATA = 2;
constexpr unsigned DELAY_OVERHEAD = 5;
constexpr unsigned CLOCKS_PER_DELAY = 1;