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fix(sdmmc): back off between CMD13 polls while waiting for card to be ready

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The loops waiting for the card to leave its busy state started their yield
backoff at 100 ms. A card is typically busy for a few milliseconds after a
write, so the backoff never fired and every write was followed by hundreds
of back-to-back CMD13 commands. Occupying the host controller like this
slows down unrelated work on both cores, not just the calling task.

Delay between polls instead, starting at CONFIG_SD_READY_POLL_PERIOD_START_US
(100 us) and doubling. Both the delay and the configured start period are
capped at one FreeRTOS tick period, where vTaskDelay() already yields and one
command per tick is not a storm. A typical wait now costs a handful of
commands instead of hundreds.

Applies to sdmmc_wait_for_idle(), sdmmc_init_sd_wait_data_ready() and
read_tuning_block().

Closes https://github.com/espressif/esp-idf/issues/19034
This commit is contained in:
Adam Múdry
2026-09-07 19:40:19 +02:00
parent 9d75e0b147
commit a2b2b36a57
4 changed files with 98 additions and 15 deletions
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components/sdmmc/sdmmc_common.c
+24 -5
View File
@@ -18,6 +18,7 @@
#include <inttypes.h>
#include "esp_log.h"
#include "freertos/FreeRTOS.h"
#include "esp_rom_sys.h"
#include "esp_timer.h"
#include "esp_private/sdmmc_common.h"
@@ -441,12 +442,33 @@ uint32_t sdmmc_get_erase_timeout_ms(const sdmmc_card_t* card, int arg, size_t er
}
}
void sdmmc_poll_delay_and_backoff(uint32_t* period_us)
{
const uint32_t us_per_tick = portTICK_PERIOD_MS * 1000;
/* Clamp on entry as well: a configured start period longer than a tick would
* otherwise be used as-is and never brought back down to the cap. */
uint32_t delay_us = MIN(*period_us, us_per_tick);
if (delay_us < us_per_tick) {
/* No blocking sleep with sub-tick resolution is available, busy-wait instead.
* The point of the delay is to keep CMD13 off the bus, which this still does. */
esp_rom_delay_us(delay_us);
} else {
vTaskDelay(1);
}
/* Stop growing once the delay reaches one tick period. At that point vTaskDelay()
* already yields and one command per tick is not a storm, so a longer delay would
* only add overshoot to the time the card is detected as ready. */
*period_us = MIN(delay_us * 2, us_per_tick);
}
esp_err_t sdmmc_wait_for_idle(sdmmc_card_t* card, uint32_t status)
{
assert(!host_is_spi(card));
esp_err_t err = ESP_OK;
size_t count = 0;
int64_t yield_delay_us = 100 * 1000; // initially 100ms
uint32_t poll_period_us = SDMMC_READY_POLL_PERIOD_START_US;
int64_t t0 = esp_timer_get_time();
int64_t t1 = 0;
/* SD mode: wait for the card to become idle based on R1 status */
@@ -455,10 +477,7 @@ esp_err_t sdmmc_wait_for_idle(sdmmc_card_t* card, uint32_t status)
if (t1 - t0 > SDMMC_READY_FOR_DATA_TIMEOUT_US) {
return ESP_ERR_TIMEOUT;
}
if (t1 - t0 > yield_delay_us) {
yield_delay_us *= 2;
vTaskDelay(1);
}
sdmmc_poll_delay_and_backoff(&poll_period_us);
err = sdmmc_send_cmd_send_status(card, &status);
if (err != ESP_OK) {
ESP_LOGE(TAG, "%s: sdmmc_send_cmd_send_status returned 0x%x", __func__, err);