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Change SPI slave approach, order of execution improved = higher MHz #60

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Merged
mkalkbrenner merged 1 commit into from
Oct 6, 2026
Merged

Change SPI slave approach, order of execution improved = higher MHz #60

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16 changes: 8 additions & 8 deletions src/pio/spi_slave_sender.pio
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Original file line number Diff line number Diff line change
@@ -1,16 +1,12 @@
.program clocked_output

; Send using an external clock on the SPI interface
; - OUT pin 0 is the data pin
; - IN pin 0 is the CLK pin
; - Autopush is enabled, threshold 32
;
; wait 0 pin 1
; Pico is a slave and constantly keeps track of incoming SCK

.wrap_target
out pins 1
wait 1 pin 0
wait 0 pin 0
wait 1 pin 0 ; rising edge: Pi is sampling the current bit
out pins, 1 ; put the NEXT bit on MISO
wait 0 pin 0 ; falling edge: prepare for the next rising edge
.wrap


Expand Down Expand Up @@ -46,6 +42,10 @@ static inline void clocked_output_program_init(PIO pio, uint sm, uint offset, ui

// Load our configuration, and start the program from the beginning
pio_sm_init(pio, sm, offset, &c);

// SPI mode 0 needs to have the first bit preloaded, will break otherwise
pio_sm_exec(pio, sm, pio_encode_out(pio_pins, 1));

pio_sm_set_enabled(pio, sm, true);
}
%}
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