This application note explains how to use a USB Flash device with the USB High Speed (HS) interfaces of the i.MX RT1170 microcontroller running uCLinux. The chip has Universal Serial Bus 2.0 Integrated PHY which contains two integrated USB 2.0 PHY macrocells capable of connecting to USB host/device systems at the USB low-, full-, and high-speed rates.
Hardware Platform
The hardware platform is the NXP i.MX RT1170 EVK board.
This demo assumes that a Micro-B to USB 2.0 A Female cable is plugged into the USB1 interface connector on the NXP i.MX RT1170 EVK board and that a pre-formatted USB Flash disk with an FAT32 partition is plugged into the USB 2.0 A Female connector of the above USB cable.
Logging Data onto USB Flash
On power-up or reset, U-Boot loads the Linux and Device Tree images from the SD Card to the SDRAM and passes control to the kernel entry point:
U-Boot SPL 2023.04 (Sep 01 2023 - 17:34:47 +0000)
Trying to boot from MMC1
U-Boot 2023.04 (Sep 01 2023 - 17:34:47 +0000)
Model: NXP imxrt1170-evk board
DRAM: 960 KiB (effective 64.9 MiB)
Core: 72 devices, 15 uclasses, devicetree: separate
MMC: FSL_SDHC: 0
Loading Environment from MMC... OK
In: serial@4007c000
Out: serial@4007c000
Err: serial@4007c000
Net: eth0: ethernet@40424000
Hit any key to stop autoboot: 0
8489874 bytes read in 755 ms (10.7 MiB/s)
## Booting kernel from Legacy Image at 80007fc0 ...
Image Name: Linux-6.1.22
Image Type: ARM Linux Multi-File Image (uncompressed)
Data Size: 8489810 Bytes = 8.1 MiB
Load Address: 80008000
Entry Point: 80008001
Contents:
Image 0: 8480224 Bytes = 8.1 MiB
Image 1: 9574 Bytes = 9.3 KiB
Verifying Checksum ... OK
## Flattened Device Tree from multi component Image at 80007FC0
Booting using the fdt at 0x8081e5ec
Working FDT set to 8081e5ec
Loading Multi-File Image
Loading Device Tree to 2032a000, end 2032f565 ... OK
Working FDT set to 2032a000
Starting kernel ...
The kernel proceeds to boot-up, initializing the configured I/O interfaces and sub-systems:
Booting Linux on physical CPU 0x0
Linux version 6.1.22 (sasha@workbench.emcraft.com)
(arm-none-eabi-gcc (GNU Arm Embedded Toolchain 10.3-2021.10)
10.3.1 20210824 (release), GNU ld (GNU Arm Embedded Toolchain
10.3-2021.10) 2.36.1.20210621) #2 Fri Sep 1 14:20:49 UTC 2023
CPU: ARMv7-M [411fc272] revision 2 (ARMv7M), cr=00000000
CPU: PIPT / VIPT nonaliasing data cache, PIPT instruction cache
OF: fdt: Machine model: NXP IMXRT1170 EVK board
Reserved memory: created DMA memory pool at 0x83f00000, size 1 MiB
OF: reserved mem: initialized node dmapool@83f00000, compatible
id shared-dma-pool
Zone ranges:
Normal [mem 0x0000000080000000-0x0000000083ffffff]
Movable zone start for each node
...
usbcore: registered new interface driver usbfs
usbcore: registered new interface driver hub
usbcore: registered new device driver usb
pps_core: LinuxPPS API ver. 1 registered
pps_core: Software ver. 5.3.6 - Copyright 2005-2007 Rodolfo Giometti
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PTP clock support registered
Bluetooth: Core ver 2.22
NET: Registered PF_BLUETOOTH protocol family
Bluetooth: HCI device and connection manager initialized
Bluetooth: HCI socket layer initialized
Bluetooth: L2CAP socket layer initialized
Bluetooth: SCO socket layer initialized
clocksource: Switched to clocksource mxc_timer1
NET: Registered PF_INET protocol family
IP idents hash table entries: 2048 (order: 2, 16384 bytes, linear)
tcp_listen_portaddr_hash hash table entries: 1024 (order: 0, 4096 bytes,
linear)
Table-perturb hash table entries: 65536 (order: 6, 262144 bytes, linear)
TCP established hash table entries: 1024 (order: 0, 4096 bytes, linear)
TCP bind hash table entries: 1024 (order: 1, 8192 bytes, linear)
TCP: Hash tables configured (established 1024 bind 1024)
UDP hash table entries: 256 (order: 0, 4096 bytes, linear)
UDP-Lite hash table entries: 256 (order: 0, 4096 bytes, linear)
NET: Registered PF_UNIX/PF_LOCAL protocol family
RPC: Registered named UNIX socket transport module.
RPC: Registered udp transport module.
RPC: Registered tcp transport module.
RPC: Registered tcp NFSv4.1 backchannel transport module.
Bus freq driver module loaded
Initialise system trusted keyrings
workingset: timestamp_bits=30 max_order=14 bucket_order=0
fuse: init (API version 7.37)
Key type asymmetric registered
Asymmetric key parser 'x509' registered
Block layer SCSI generic (bsg) driver version 0.4 loaded (major 251)
io scheduler mq-deadline registered
io scheduler kyber registered
4007c000.serial: ttyLP0 at MMIO 0x4007c010 (irq = 447, base_baud =
1500000) is a FSL_LPUART
fsl-lpuart 4007c000.serial: Serial: Console lpuart rounded baud
ratefrom 187500 to 115200
printk: console [ttyLP0] enabled
PPP generic driver version 2.4.2
PPP BSD Compression module registered
PPP Deflate Compression module registered
usbcore: registered new interface driver rt2800usb
usbcore: registered new interface driver cdc_acm
cdc_acm: USB Abstract Control Model driver for USB modems and ISDN
adapters
usbcore: registered new interface driver uas
usbcore: registered new interface driver usb-storage
i2c_dev: i2c /dev entries driver
usbcore: registered new interface driver btusb
sdhci: Secure Digital Host Controller Interface driver
sdhci: Copyright(c) Pierre Ossman
sdhci-pltfm: SDHCI platform and OF driver helper
usbcore: registered new interface driver usbhid
usbhid: USB HID core driver
NET: Registered PF_PACKET protocol family
mmc0 bounce up to 128 segments into one, max segment size 65536 bytes
Bluetooth: RFCOMM TTY layer initialized
Bluetooth: RFCOMM socket layer initialized
Bluetooth: RFCOMM ver 1.11
ARMv7-M VFP coprocessor found
VFP: Double precision floating points are supported
Loading compiled-in X.509 certificates
mmc0: SDHCI controller on 40418000.usdhc [40418000.usdhc] using DMA
input: gpio-keys as /devices/platform/gpio-keys/input/input0
cfg80211: Loading compiled-in X.509 certificates for regulatory database
cfg80211: Loaded X.509 cert 'sforshee: 00b28ddf47aef9cea7'
platform regulatory.0: Direct firmware load for regulatory.db failed with
error -2
cfg80211: failed to load regulatory.db
Freeing unused kernel image (initmem) memory: 3556K
This architecture does not have kernel memory protection.
Run /init as init process
[72] Jan 01 00:00:01 Running in background
/ # mmc0: host does not support reading read-only switch, assuming
write-enable
mmc0: new high speed SDHC card at address 59b4
mmcblk0: mmc0:59b4 USD 7.39 GiB
mmcblk0: p1
Micrel KSZ8081 or KSZ8091 40424000.ethernet-1:02: attached PHY driver
(mii_bus:phy_addr=40424000.ethernet-1:02, irq=POLL)
fec 40424000.ethernet eth0: Link is Up - 100Mbps/Full - flow control off
USB OTG 1 Controller (USB OTG)
Connect just a Micro-B to USB 2.0 A Female cable to the USB1 connector.
Connect USB Flash device to the cable. Observe it is detected and configured:
ci_hdrc ci_hdrc.0: EHCI Host Controller
ci_hdrc ci_hdrc.0: new USB bus registered, assigned bus number 1
ci_hdrc ci_hdrc.0: USB 2.0 started, EHCI 1.00
hub 1-0:1.0: USB hub found
hub 1-0:1.0: 1 port detected
usb 1-1: new high-speed USB device number 2 using ci_hdrc
usb-storage 1-1:1.0: USB Mass Storage device detected
scsi host0: usb-storage 1-1:1.0
scsi 0:0:0:0: Direct-Access Generic Flash Disk 8.07 PQ: 0 ANSI: 2
sd 0:0:0:0: [sda] 8228864 512-byte logical blocks: (4.21 GB/3.92 GiB)
sd 0:0:0:0: [sda] Write Protect is off
sd 0:0:0:0: [sda] No Caching mode page found
sd 0:0:0:0: [sda] Assuming drive cache: write through
sda: sda1
sd 0:0:0:0: [sda] Attached SCSI removable disk
At this point, the USB Flash is accessible as a disk. The following command is used to examine the disk, which is detected as a 4GBytes disk partitioned to have a single empty FAT32 partition:
/ # fdisk -l /dev/sda
Disk /dev/sda: 4018 MB, 4213178368 bytes, 8228864 sectors
512 cylinders, 255 heads, 63 sectors/track
Units: sectors of 1 * 512 = 512 bytes
Device Boot StartCHS EndCHS StartLBA EndLBA Sectors
Size Id Type
/dev/sda1 * 0,32,33 511,254,63 2048 8228863 8226816
4017M c Win95 FAT32 (LBA)
Partition 1 has different physical/logical end:
phys=(511,254,63) logical=(512,56,56)
Let's mount the FAT32 file system. As expected, it is empty at this point:
/ # mount /dev/sda1 /mnt/usbflash
/ # ls -l /mnt/usbflash/
drwxr-xr-x 2 root root 4096 May 25 2023 System Volume Information
/ #
Let's "harvest" some data and store what is collected into a file on the USB Flash disk. In this demo, we emulate a data stream by taking a snapshot of the system time each second:
~ # while true; do date >> /mnt/usbflash/data.log; sleep 1; done
Having let the "data harvesting" run for a few seconds, let's interrupt it (by pressing ^-C) and take a look at what data we have collected:
/ # cat /mnt/usbflash/data.log
Thu Jan 1 00:11:27 UTC 1970
Thu Jan 1 00:11:28 UTC 1970
Thu Jan 1 00:11:29 UTC 1970
Thu Jan 1 00:11:30 UTC 1970
Thu Jan 1 00:11:31 UTC 1970
Thu Jan 1 00:11:32 UTC 1970
Thu Jan 1 00:11:33 UTC 1970
Thu Jan 1 00:11:34 UTC 1970
Thu Jan 1 00:11:35 UTC 1970
Thu Jan 1 00:11:36 UTC 1970
/ #
Now, let's unmount the USB Flash and unplug the device from the USB cable:
/ # umount /mnt/usbflash
At this point, the USB Flash device can be taken to a PC for further data processing. Just plug in the USB Flash into a USB port on your PC and the PC software will be able to mount the device as a FAT32 file system.
usb 1-1: USB disconnect, device number 2
ci_hdrc ci_hdrc.0: remove, state 1
usb usb1: USB disconnect, device number 1
ci_hdrc ci_hdrc.0: USB bus 1 deregistered
Note that the format of Windows and Unix text files differs slightly. In Windows, lines end with both the line feed and carriage return ASCII characters, but Unix uses only a line feed. As a consequence, some Windows applications will not show the line breaks in Unix-format files. Assuming that data is stored in a text file (vs a binary file) and Windows is a data processing host, Linux data harvesting applications should take care of the difference by adding a carriage return character to data logs.
Note further that you can hot plug your USB Flash device on the running system at any time:
ci_hdrc ci_hdrc.1: EHCI Host Controller
ci_hdrc ci_hdrc.1: new USB bus registered, assigned bus number 1
ci_hdrc ci_hdrc.1: USB 2.0 started, EHCI 1.00
hub 1-0:1.0: USB hub found
hub 1-0:1.0: 1 port detected
usb 1-1: new high-speed USB device number 2 using ci_hdrc
usb-storage 1-1:1.0: USB Mass Storage device detected
scsi host0: usb-storage 1-1:1.0
scsi 0:0:0:0: Direct-Access Generic Flash Disk 8.07 PQ: 0 ANSI: 2
sd 0:0:0:0: [sda] 8228864 512-byte logical blocks: (4.21 GB/3.92 GiB)
sd 0:0:0:0: [sda] Write Protect is off
sd 0:0:0:0: [sda] No Caching mode page found
sd 0:0:0:0: [sda] Assuming drive cache: write through
sda: sda1
sd 0:0:0:0: [sda] Attached SCSI removable disk
/ # mount /dev/sda1 /mnt/usbflash
/ # ls -l /mnt/usbflash
drwxr-xr-x 2 root root 4096 May 25 2023 System Volume Information
-rwxr-xr-x 1 root root 232 Jan 1 1980 data.log
/ # umount /mnt/usbflash
Data Synchronization Considerations
It is important to understand that VFAT supports write-back in Linux, which means that file changes do not go to the physical media straight away and instead are cached in memory and go to the Flash at a later time. This helps to reduce amount to I/O to the physical Flash, resulting in a better performance overall.
The write-back creates a certain issue for embedded devices however. If the power to the device is shut down unexpectedly, or the USB Flash is unplugged without a proper unmount or sync, some of latest file changes may be lost.
As it is typical with Linux, the issue can be handled in many ways. Data synchronization can be ensured on a per-file, per-subtree, per-filesystem or system-wide basis. Synchronization can be transparent for the user or may require issuing an explicit API call or a shell command.
The most obvious solution is to mount the file system in synchronous mode (note the -o sync parameter in the call below):
/ # mount -o sync /dev/sda1 /mnt/usbflash
/ # mount
rootfs on / type rootfs (rw)
proc on /proc type proc (rw,relatime)
sysfs on /sys type sysfs (rw,relatime)
devtmpfs on /dev type devtmpfs (rw,nosuid,relatime)
devpts on /dev/pts type devpts (rw,relatime,gid=5,mode=620,ptmxmode=000)
/dev/sda1 on /mnt/usbflash type vfat (rw,sync,relatime,fmask=0022,dmask=0022,
codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro)
When the file system is mounted for synchronous operation, Linux guarantees that data is written to the physical media before any write()returns to a calling application. The tradeoff is that written data is no longer cached in memory, which reduces the write performance substantially.
