Freescale USB stack v4.1.1

[izmile]

Hi,

I am using Freescale USB stack v4.1.1 on K22 processor. I am defining my device descriptors on RAM memory as shown below.

uint_8 g_device_descriptor[DEVICE_DESCRIPTOR_SIZE]=

{

DEVICE_DESCRIPTOR_SIZE,                /*  Device Descriptor Size         */

USB_DEVICE_DESCRIPTOR,                 /*  Device Type of descriptor      */

...

}

If I change the device descriptor (or any other descriptor) to FLASH area (as shown below) then I don't get proper USB enumeration.. Does Freescale USB stack work only with descriptors defined in RAM memory? I checked the K22 datasheet/reference, there is no restriction on the address in the BDT entry.

uint_8 const g_device_descriptor[DEVICE_DESCRIPTOR_SIZE]=

{

DEVICE_DESCRIPTOR_SIZE,                /*  Device Descriptor Size         */

USB_DEVICE_DESCRIPTOR,                 /*  Device Type of descriptor      */

...

}

Could any one shed some light on this please?

Thanks,

-Ismail

[Kan_Li]

Hi Ismail,

If you put code running in flash as well, you might have to reconfigure the Crossbar Switch to let USB has higher priority than ARM core, please kindly refer to Priority Registers Slave(AXBS_PRSn) for more details.

Have a great day,
Kan

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[izmile]

Hi Mark and Li,

You both are correct. Now, I could make the USB working from flash.

Thanks a lot.

-Ismail

[mjbcswitzerland · Accepted solution]

Hi Ismail

The USB controller can't access Flash by default so you need to enable its rights in the flash access protection register:

FMC_PFAPR |= FMC_FPAPR_USB_FS;

The USB FS is bus master 4 in the K22 so

#define FMC_FPAPR_USB_FS

FMC_PFAPR_M4AP_RD

(which is 0x00000100)

Regards

Mark

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