STM32L USB Driver for Keil

The USB device engine on STM32L is almost same as STM32F103.
The only difference is the D+ pull-up resistor: STM32L has on-chip pull-up.
But this pull-up isn't compliant to the USB spec, as this errata tells, on all revision.

STM32L15xx errata sheet
www.st.com/.../CD00278726.pdf
2.5.1 Pull-up resistor has a value lower than 1.5kOhm
Description: The pull-up resistor on USB line is requested to have a nominal value of 1.5kOhm, whereas the characterization of the internal pull-up shows a value between 0.81 and 0.95 kOhm o the full temperature range.
Workaround: An external pull-up resistor controlled by a GPIO can be used.

After all, STM32L requires an external pull-up resistor. In this configuration, there is no difference from STM32F103.

Therefore, you may start with usbd_STM32F103.c for STM32F103

Tsuneo

Auu, copy-paste mistake..
> Therefore, you may start with usbd_STM32F103.c for STM32F103

Therefore, you may start with usbd_STM32F103.c for STM32L

Tsuneo

Hi to all and thanx to Tsuneo, as usual.

This is an obvious starting point. So - of course - I inspected the usbd_STM32F103.c source.
Unfortunately there seem to be so many major differences between F and L line.
If only looking at the ST usb core, there are about 70 "#ifdef STM32F10X_CL"
statements distinguishing between the chips.

Although I feel quite safe and experienced at the "Report-Level" I am certainly not the driver god to code such a thing in a wink.

I am not satisfied with the support that Keil gives in this particular area.
Long time ago (16 Nov 2010) they claimed to support this ST-line
(see http://www.keil.com/pr/article/1225.htm)
but as of today, there is still no more than just a blinky sample and no USB at all.

best regards
Uli

I am also looking at the ST32L for a project and really need to use the USB port.

There seems to be plenty of support for the 'F' series with examples etc but hardly anything for the 'L' series.

I think that it should not be too much work for Keil to port the F driver over to the 'L' devices.

Trev

Hi, here is a port of KEIL RL-USB HID to STM32L-DISCOVERY board.

homepage2.nifty.com/.../STM32L_DISC_KEIL_RL_HID.zip

A couple of notes of porting,

A) Hardware - USB connector
STM32L-DISCOVERY doesn't have USB receptacle. A USB B type receptacle is connected as follows. Also, an external 1k5 D+ pull-up resistor is placed across PC12 and D+. As mentioned on above post, the on-chip pull-up is not recommended.

 STM32L               USB
DISCOVERY          receptacle

 PA11 --------------- D-

 PA12 -----------+--- D+
                 |
 PC12 --- 1k5 ---+

 GND  --------------- GND

B) Hardware - Crystal
STM32L-DISCOVERY board has pads for a crystal, but not populated.
These components are added.
- X3: 8 MHz crystal
- C21, C22: 22pF
- R30: 220 Ohm

The external crystal is required, because the tolerance of HSI OSC (+/-1%) is not enough for USB operation.

C) Firmware - porting steps
1) Start on MCBSTM32 RL-USB HID example C:\Keil\ARM\Boards\Keil\MCBSTM32\RL\USB\Device\HID

2) Replace "startup" and "system" file with those of STM32L, on Blinky example.
(C:\Keil\ARM\Boards\ST\STM32L-Discovery\Blinky)
- startup_stm32f10x_md.s --> startup_stm32l1xx_md.s
- system_stm32f10x.c --> system_stm32l1xx.c

Fortunately, Blinky "system" file has been already tuned for USB operation (8MHz crystal - HSE OSC and 96MHz PLL), without any change.

3) Modify usbd_STM32F103.c for STM32L differences.
USB Interrupt
- USBD_IntrEna() Replace USB_LP_CAN1_RX0_IRQn with USB_LP_IRQn
- USB_LP_CAN1_RX0_IRQHandler() Rename this function name with USB_LP_IRQHandler()

USB Connection port (PC12)
- USBD_Init() Enable GPIO C
- USBD_Connect() Switch PC12 between floating input and push-pull output, to emulate high-side open-drain switch.

4) Change port assignment of LEDs and a switch on usbd_user_hid.c
- usbd_hid_init()
- usbd_hid_get_report()
- usbd_hid_set_report()

5) Replace #include of stm32f10x.h with stm32l1xx.h on USBD_Demo.c, usbd_user_hid.c and usbd_STM32F103.c

6) Delete LCD support
- LCD_4bit.c
- USBD_Demo.c, main()

7) On uVision, Project menu > Options dialog
- Device tab: select STM32L152RB
- C/C++ tab: enter STM32L1XX_MD on Define box
- Debug tab: Use "ST-Link debugger", Setting > Port: JTAG -> SW
- Utilities tab: Use "ST-Link debugger", Setting > Programming algorithm: STM32L15x Low Power Flash

I believe I've listed up all of changes, but to make it sure, compare the source files with a "diff" utility ;-)

Enjoy!

Tsuneo

Tsuneo,

for now many thanks. Your assistance is really invaluable. I will check the project shortly and return here with results.

Uli

Has anyone already done it or have any guidence on what I may have to do to take the stm32F2xx HS USB port driver and remove the external Phy from it

Curerntly I am using the ST code and ETFS and thopuhgj I have no problems at the moment with it I would prefer eventually move to just one FS.

thanks in advance

Thanks Tsuneo!

I'm totally a newbie with microcontroller and currently trying to play with the USB function on STM32L-Discovery. I got stuck on how to port the STM USB library to the discovery board for a couple days and found your post a very helpful guide!

I wonder if you used the licensed version of Keil toolchain? I downloaded your code and ran it with Keil, it showed the following error:

 .\Test.axf: Error: L9937E: RL-ARM is not allowed with this license

Thanks a lot!

Vicki

Hello!

I'm trying to get my STM32L USB device to communicate with PC. Actually i'm stuck at just building the project files for Tsuneo's example HID project and I've come across a problem already.

.\Flash\HID.axf: Error: L9937E: RL-ARM is not allowed with this license

I have MDK-ARM Standard license. So, does that mean I can't use USB device if I dont have pro license? I don't use RTX (BTW: it is possible to use USBd without RTOS/RTX, right?)

Thanks for answers.

J