Poor Read/Write Performance with Zephyr SDIF Driver on LPCXpresso55S69-EVK

wima88 · ‎06-24-2025

When evaluating the LPC55S69-EVK, I noticed significantly slower read/write speeds with Zephyr’s USB mass storage (using the SDIF driver) compared to the MCUXpresso SDK example.

Benchmark Results

Below are the performance comparisons using CrystalDiskMark 8.0.6:

1. MCUXpresso SDK Example (lpcxpresso55s69_dev_msc_disk_freertos_cm33_core0)

[Read]
  SEQ 1MiB: 10.903 MB/s | RND 4KiB: 4.204 MB/s
[Write]
  SEQ 1MiB: 7.756 MB/s  | RND 4KiB: 3.286 MB/s

2. Zephyr (Legacy USB Stack)

[Read]
  SEQ 1MiB: 1.048 MB/s | RND 4KiB: 0.985 MB/s
[Write]
  SEQ 1MiB: 0.209 MB/s | RND 4KiB: 0.351 MB/s

~10x slower than MCUXpresso SDK.

3. Zephyr (USB Device Next Stack)

[Read]
  SEQ 1MiB: 1.676 MB/s | RND 4KiB: 1.489 MB/s
[Write]
  SEQ 1MiB: 0.628 MB/s | RND 4KiB: 0.830 MB/s

*Still ~5-6x slower than MCUXpresso SDK.*

Debugging Attempts

Enabled Zephyr SDHC & SD card logs – no errors detected.
Confirmed SD card initialization (3.3V, 50MHz clock, correct block size).
Logs show successful SDIF clock configuration (24MHz → 50MHz).

[00:00:00.000] <dbg> sd: sd_init_io: Host controller support 3.3V max  
[00:00:01.000] <dbg> sdif: mcux_sdif_set_io: SDIF clock set to 400000  
[00:00:01.376] <dbg> sd: sdmmc_read_csd: Card block count 124735488, block size 512  
[00:00:01.376] <dbg> sdif: mcux_sdif_set_io: SDIF clock set to 24000000  
[00:00:01.379] <dbg> sd: sdmmc_set_bus_speed: Setting bus clock to: 50000000

Environment

Board: LPC55S69-EVK
Zephyr Version: commit :c2d52c7f4b53a3e3691a7e6fa15af83ef72446cc(4.1.99)

Are their any Kconfig option or overlay that I need to modify ?

I’d appreciate any insights or suggestions to debug this further

Thanks in advance!

wima88 · ‎07-07-2025

@Harry_Zhang Any Update on this issue? I tested the FRDM-MCXN947 (with Zephyr) which uses the imx driver instead of the lpc driver. and results are pretty much the same as above

Thanks

Harry_Zhang · ‎07-14-2025

Hi @wima88

Could you please try adding the following optimizations

CONFIG_MCUX_SDIF_DMA_BUFFER_SIZE=512
CONFIG_SPEED_OPTIMIZATIONS=y
CONFIG_SDIO_STACK=y
CONFIG_MPU=n
CONFIG_ASSERT=n
CONFIG_LOG=n
CONFIG_LOG_DEFAULT_LEVEL=0

BR

Harry

wima88 · ‎07-15-2025

Hi Harry ,

Thanks for getting back to me. with suggested Konig options I was managed to get around 2.54 MB/s.

[Read]
SEQ 1MiB (Q= 1, T= 1): 2.516 MB/s [ 2.4 IOPS] <412859.66 us>
RND 4KiB (Q= 1, T= 1): 2.033 MB/s [ 496.3 IOPS] < 2011.94 us>

I wonder, could USB stack be the bottle neck?

Harry_Zhang · ‎07-22-2025

Hi @wima88

Another USB optimizations that you could give a try.

CONFIG_UDC_BUF_COUNT=128
CONFIG_UDC_WORKQUEUE_STACK_SIZE=2048
CONFIG_UDC_WORKQUEUE_PRIORITY=0

BR

Harry

wima88 · ‎07-23-2025

Thanks for the suggestions.

Despite all the optimizations and changes, the best I could reach was 3.1 MB/s. Have you identified the root cause of the performance issue yet? Frankly, I doubt any amount of system tuning alone will get us to full performance without addressing the underlying problem.

Wimansha

Harry_Zhang · ‎07-08-2025

Hi @wima88

We are investigating this issue, I will inform you as soon as there is a result.

BR

Harry

Harry_Zhang · ‎06-25-2025

Hi @wima88

May i ask how to tested it?

I want to test it.

BR

Harry

wima88 · ‎06-25-2025

Hi Harry ,

Hi,

I use CrystalDiskMark as my benchmarking tool(https://crystalmark.info/en). Here’s my setup and process:

MCUXpresso SDK Setup:

Modified jumper P4 voltage from 1.8V to 3.3V (as per user guide Table 1, P21).
Downloaded the SDK example (v25.03.00) via the MCUXpresso extension in VSCode.
Built and flashed the lpcxpresso55s69_dev_msc_disk_freertos_cm33_core0 example.
After reset, the serial terminal showed the prompt: "Please insert disk."
Used a SanDisk Class 3 V30 SD card.
Connected P9 (HS-USB) and configured CrystalDiskMark (see attached screenshot).
Tested with:
- 1MB block size
- 1 Queue, 1 Thread
- 9 iterations of a 32MB file

Zephyr Setup:

Used the same development environment as above.

Legacy USB Stack:

Example: zephyr/samples/subsys/usb/mass
No modifications made.
Build command:

west build -p -b lpcxpresso55s69/lpc55s69/cpu0
west flash

USB Next Stack:

Modified next_usb_prj.conf as follows:

CONFIG_DISK_ACCESS=y  
CONFIG_FILE_SYSTEM=y  
CONFIG_FAT_FILESYSTEM_ELM=y  
CONFIG_PRINTK=y  

CONFIG_DISK_DRIVERS=y  
CONFIG_DISK_DRIVER_SDMMC=y  

CONFIG_SDHC_LOG_LEVEL_DBG=y  
CONFIG_SD_LOG_LEVEL_DBG=y  
CONFIG_LOG_BUFFER_SIZE=2048  

CONFIG_USBD_MSC_STACK_SIZE=4096  
CONFIG_USBD_MSC_LUNS_PER_INSTANCE=5  
CONFIG_USBD_MSC_SCSI_BUFFER_SIZE=2048

Build Command

west build -p -b lpcxpresso55s69/lpc55s69/cpu0 -- -DCONF_FILE=usbd_next_prj.conf  
west flash

Testing:

Used the same CrystalDiskMark setup for all three cases.
No overlay files were used in either Zephyr example.

Let me know if you need any further details!

Thank You