This requires doing raw writes to a large contiguous block on the card. You must design your app to buffer data during the busy periods. The card may indicate busy during the time the card controller is writing and moving data.įor a class 10 SDHC card, AU size is up to 4MB and RU size is 512 KB. RUs are part of a larger AU, Allocation Unit.Īs you write, the card prepares new erased AUs by copying use RUs from the old AU and writing new RUs. The problem with fast writes to SD cards is that modern SD cards emulate 512 byte sectors in a much larger RU, Recording Unit. Unfortunatly I'm only able to get a writing speed of around 400KB/s with my ESP32 and a class 10 16gb microsdhc. I know the commands of 'writeBlock', writeStart, writeData, writeStop to do this. Hello there, I'm interested in logging data directly in Raw bytes on my non partioned sd Card. I didn't calculate the rate and was thinking of fast logging like three 2.4 msps ADCs on a STM32 which can deliver over 10 MB/sec. Probably none of this matters since you have so much RAM and a fairly slow data rate. if possible try to at least maintain writes on sector boundaries. If you make a true wave file, writing the header can cause miss alignment so your writes are not aligned with clusters or sectors. Unless you write on cluster boundaries your 32 KB buffer will result in two writes since the writes will not be aligned on cluster boundaries. Writing blocks larger than 32 KB won't help because SdFat limits internal writes to the current cluster. I assume the the rate for a wave file is 2X3X96 KB/sec which is under 600 KB/sec. You probably can get away with your buffering scheme since 24/96/stereo is fairly slow.

To achieve really high speeds you must account for this size. It is the physical layout of flash in the SD.įlash pages are huge in the SD, 512 KB in a modern SD. The file system's 32 KB cluster has nothing to do with the delay.

Disabling spi arduino sdfat