Initial Release

pio/pwm/CMakeLists.txt

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+add_executable(pio_pwm)
+
+pico_generate_pio_header(pio_pwm ${CMAKE_CURRENT_LIST_DIR}/pwm.pio)
+
+target_sources(pio_pwm PRIVATE pwm.c)
+
+target_link_libraries(pio_pwm PRIVATE pico_stdlib hardware_pio)
+pico_add_extra_outputs(pio_pwm)
+
+# add url via pico_set_program_url
+example_auto_set_url(pio_pwm)

pio/pwm/pwm.c

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+/**
+ * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <stdio.h>
+
+#include "pico/stdlib.h"
+#include "hardware/pio.h"
+#include "pwm.pio.h"
+
+// Write `period` to the input shift register
+void pio_pwm_set_period(PIO pio, uint sm, uint32_t period) {
+    pio_sm_set_enabled(pio, sm, false);
+    pio_sm_put_blocking(pio, sm, period);
+    pio_sm_exec(pio, sm, pio_encode_pull(false, false));
+    pio_sm_exec(pio, sm, pio_encode_out(pio_isr, 32));
+    pio_sm_set_enabled(pio, sm, true);
+}
+
+// Write `level` to TX FIFO. State machine will copy this into X.
+void pio_pwm_set_level(PIO pio, uint sm, uint32_t level) {
+    pio_sm_put_blocking(pio, sm, level);
+}
+
+int main() {
+    stdio_init_all();
+
+    // todo get free sm
+    PIO pio = pio0;
+    int sm = 0;
+    uint offset = pio_add_program(pio, &pwm_program);
+    printf("Loaded program at %d\n", offset);
+
+    pwm_program_init(pio, sm, offset, 25);
+    pio_pwm_set_period(pio, sm, (1u << 16) - 1);
+
+    int level = 0;
+    while (true) {
+        printf("Level = %d\n", level);
+        pio_pwm_set_level(pio, sm, level * level);
+        level = (level + 1) % 256;
+        sleep_ms(10);
+    }
+}

pio/pwm/pwm.pio

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+;
+; Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
+;
+; SPDX-License-Identifier: BSD-3-Clause
+;
+
+; Side-set pin 0 is used for PWM output
+
+.program pwm
+.side_set 1 opt
+
+    pull noblock    side 0 ; Pull from FIFO to OSR if available, else copy X to OSR.
+    mov x, osr             ; Copy most-recently-pulled value back to scratch X
+    mov y, isr             ; ISR contains PWM period. Y used as counter.
+countloop:
+    jmp x!=y noset         ; Set pin high if X == Y, keep the two paths length matched
+    jmp skip        side 1
+noset:
+    nop                    ; Single dummy cycle to keep the two paths the same length
+skip:
+    jmp y-- countloop      ; Loop until Y hits 0, then pull a fresh PWM value from FIFO
+
+% c-sdk {
+static inline void pwm_program_init(PIO pio, uint sm, uint offset, uint pin) {
+   pio_gpio_init(pio, pin);
+   pio_sm_set_consecutive_pindirs(pio, sm, pin, 1, true);
+   pio_sm_config c = pwm_program_get_default_config(offset);
+   sm_config_set_sideset_pins(&c, pin);
+   pio_sm_init(pio, sm, offset, &c);
+}
+%}