adafruit · Sola85 · Jul 18, 2025 · Jul 19, 2025
diff --git a/ports/espressif/common-hal/pulseio/PulseIn.c b/ports/espressif/common-hal/pulseio/PulseIn.c
@@ -74,14 +74,20 @@ static bool _done_callback(rmt_channel_handle_t rx_chan,
 
 void common_hal_pulseio_pulsein_construct(pulseio_pulsein_obj_t *self, const mcu_pin_obj_t *pin,
     uint16_t maxlen, bool idle_state) {
+
+    // Only use dma when necessary, since dma-rmt might not be available.
+    // If dma is necessary but not available, this will raise an error below.
+    bool use_dma = maxlen > 128;
+
     self->buffer = (uint16_t *)m_malloc_without_collect(maxlen * sizeof(uint16_t));
     if (self->buffer == NULL) {
         m_malloc_fail(maxlen * sizeof(uint16_t));
     }
     // We add one to the maxlen version to ensure that two symbols at lease are
     // captured because we may skip the first portion of a symbol.
-    self->raw_symbols_size = MIN(64, maxlen / 2 + 1) * sizeof(rmt_symbol_word_t);
-    self->raw_symbols = (rmt_symbol_word_t *)m_malloc_without_collect(self->raw_symbols_size);
+    self->raw_symbols_size = (maxlen / 2 + 1) * sizeof(rmt_symbol_word_t);
+    // RMT DMA mode cannot access PSRAM -> ensure raw_symbols is in internal ram
+    self->raw_symbols = (rmt_symbol_word_t *)port_malloc(self->raw_symbols_size, use_dma);
     if (self->raw_symbols == NULL) {
         m_free(self->buffer);
         m_malloc_fail(self->raw_symbols_size);
@@ -109,17 +115,31 @@ void common_hal_pulseio_pulsein_construct(pulseio_pulsein_obj_t *self, const mcu
         .clk_src = RMT_CLK_SRC_DEFAULT,
         // 2 us resolution so we can capture 65ms pulses. The RMT period is only 15 bits.
         .resolution_hz = 1000000 / 2,
-        .mem_block_symbols = SOC_RMT_MEM_WORDS_PER_CHANNEL,
+        .mem_block_symbols = use_dma ? self->raw_symbols_size : SOC_RMT_MEM_WORDS_PER_CHANNEL,
+        .flags.with_dma = use_dma
     };
-    // If we fail here, the buffers allocated above will be garbage collected.
-    CHECK_ESP_RESULT(rmt_new_rx_channel(&config, &self->channel));
+    // If we fail here, the self->buffer will be garbage collected.
+    esp_err_t result = rmt_new_rx_channel(&config, &self->channel);
+    if (result != ESP_OK) {
+        port_free(self->raw_symbols);
+        if (result == ESP_ERR_NOT_SUPPORTED || result == ESP_ERR_NOT_FOUND) {
+            // DMA not available, cannot record long pulse sequences.
+            mp_raise_ValueError_varg(MP_ERROR_TEXT("Invalid %q"), MP_QSTR_maxlen);
+        } else {
+            raise_esp_error(result);
+        }
+    }
 
     rmt_rx_event_callbacks_t rx_callback = {
         .on_recv_done = _done_callback
     };
     rmt_rx_register_event_callbacks(self->channel, &rx_callback, self);
     rmt_enable(self->channel);
-    rmt_receive(self->channel, self->raw_symbols, self->raw_symbols_size, &rx_config);
+    result = rmt_receive(self->channel, self->raw_symbols, self->raw_symbols_size, &rx_config);
+    if (result != ESP_OK) {
+        port_free(self->raw_symbols);
+        raise_esp_error(result);
+    }
 }
 
 bool common_hal_pulseio_pulsein_deinited(pulseio_pulsein_obj_t *self) {

diff --git a/shared-bindings/pulseio/PulseIn.c b/shared-bindings/pulseio/PulseIn.c
@@ -33,6 +33,10 @@
 //|         :param bool idle_state: Idle state of the pin. At start and after `resume`
 //|           the first recorded pulse will the opposite state from idle.
 //|
+//|         **Limitations**: The `maxlen` parameter is limited depending on the specific board.
+//|         On most ESP32 variants the limit is 128. On ESP32-S3 and ESP32-P4 the first `PulseIn` instance
+//|         can use `maxlen` up to available RAM; all subsequent instances are limited to 128.
+//|
 //|         Read a short series of pulses::
 //|
 //|           import pulseio