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ixtab · 09-26-2012, 03:40 AM

A few more thoughts on the imx_usb tool:

I can't for the life of me figure out why I can't access the DRAM. I looked at the Reference Manual (for convenience, the Memory map is on page 150, while the USB mode is on page 471).

I have tried to fiddle around a bit with modifying some memory, the rationale being: if it's possible to upload an initrd in addition to a custom u-boot image (which would load that initrd), then we'd essentially be able to control the entire boot process, without having to write to the "disk" at all. So the first step was to simply try and upload something to the RAM - but it fails consistently. In fact, I seem to be able to access pretty much every memory location - with the exception of the DRAM

I checked and double-checked it: the data going over the line is correct (you can simply #define DEBUG in the source file, and it'll dump reads and writes, so I could cross-check with the reference manual), but as soon as I even try to read 0x70000000, the result is libusb error -4 (LIBUSB_ERROR_NO_DEVICE).

Does anyone have an explanation for this? Could it be that the DRAM isn't initialized yet? And if so... which options do we have? For now, it seems like the only region that we can really access is the 128kB of OCRAM starting at F8000000. That's obviously enough for putting u-boot in there, but not much more.

Thinking aloud: maybe a custom u-boot that downloads a kernel using tftp could do...

09-26-2012, 03:40 AM	#232
ixtab (offline) Posts: 2,907 Karma: 6736092 Join Date: Dec 2011 Device: K3, K4, K5, KPW, KPW2	A few more thoughts on the imx_usb tool: I can't for the life of me figure out why I can't access the DRAM. I looked at the Reference Manual (for convenience, the Memory map is on page 150, while the USB mode is on page 471). I have tried to fiddle around a bit with modifying some memory, the rationale being: if it's possible to upload an initrd in addition to a custom u-boot image (which would load that initrd), then we'd essentially be able to control the entire boot process, without having to write to the "disk" at all. So the first step was to simply try and upload something to the RAM - but it fails consistently. In fact, I seem to be able to access pretty much every memory location - with the exception of the DRAM I checked and double-checked it: the data going over the line is correct (you can simply #define DEBUG in the source file, and it'll dump reads and writes, so I could cross-check with the reference manual), but as soon as I even try to read 0x70000000, the result is libusb error -4 (LIBUSB_ERROR_NO_DEVICE). Does anyone have an explanation for this? Could it be that the DRAM isn't initialized yet? And if so... which options do we have? For now, it seems like the only region that we can really access is the 128kB of OCRAM starting at F8000000. That's obviously enough for putting u-boot in there, but not much more. Thinking aloud: maybe a custom u-boot that downloads a kernel using tftp could do...