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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.

1. 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.

2. 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:

...

Code Block
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 
<
 giometti@linux.it>
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

2.1. USB OTG 1 Controller (USB OTG)

  1. Connect just a Micro-B to USB 2.0 A Female cable to the USB1 connector.

  2. Connect USB Flash device to the cable. Observe it is detected and configured:

    Code Block
    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

...

Code Block
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

3. 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.

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