File loading speed from sd to ram

[ledlaux]

Need some help with SD card speed settings, because it is running in 25MHz mode only (I think so). Loading of 24mb soundfont into memory takes 19,4s to read which is very slow (1.15mb/s). Kernel reports in the log that it found 3.0 class card.

Hardware:
RPI Zero 2w
10 class SDHC 30mb/s 32gb card formatted with 32 KB cluster size.

I have set in

kernel.h

#include <SDCard/emmc.h>

CEMMCDevice         m_EMMC;

kernel.cpp:

CKernel::CKernel (void)
:   ...
    m_EMMC (&m_Interrupt, &m_Timer, &m_ActLED)
}

if (bOK)
    {
        bOK = m_EMMC.Initialize ();
        if (!bOK)
        {
            m_Logger.Write (FromKernel, LogError, "Failed to initialize SD host driver");
        }
    }

config.txt

[all]
arm_64bit=0
kernel=kernel8.img
boot_delay=0
disable_splash=1
force_eeprom_read=0
hdmi_force_hotplug=1
dtparam=i2s=on

cmdline.txt
usbspeed=full fast=true loglevel=4

sysconfig.h

#define NO_SDHOST
#define SD_HIGH_SPEED

emmc.cpp
#define SD_4BIT_DATA

Tested both single bulk FileRead calls and 32 KB / 64 KB chunked read loops. Result is always the same. What am I missing?

[ledlaux]

Needs to be mentioned that <circle/fs/fat/fatfs.h> is used, as I wanted to test the builtin methods. Is it the culprit?

[Xalior]

Have you tried burst/larger blocks at the underlying block layer - basically a small read ahead caching routine - to optimise the bulk transfer nature? I wrote a fairly primitive one, when developing some of my game libs - it’s broken out to its own discrete functions here: https://github.com/Xalior/circle-libsdl2/tree/main/circle-diskcache

…

-Good luck, Dx

Sent from my iPhone

[ledlaux]

Very interesting, i will look how this can be integrated in my project. It is using addon/fatfs library right?

[rsta2]

Needs to be mentioned that <circle/fs/fat/fatfs.h> is used, as I wanted to test the builtin methods. Is it the culprit?

No, the native Circle FAT filesystem driver is relatively slow. You should use FatFs in addon/fatfs/ instead, because it's much faster and has more features. See the sample in addon/fatfs/sample/. Normally you can read the whole file with one call to f_read(), which should be the fastest. The SD card support in Circle is not perfect, but you should be able to read your file in about 2 seconds.

[ledlaux]

Thanks! I will change project to use addon/fatfs and check the speeds. Will report back.

[ledlaux]

Yes, that was it, Circle native FAT driver is usable, but not for processing couple MB files. Changed to /addon/fatfs and used f_read(). Now it loads as it should. Big thanks! It helped my project a lot.