ESP8266 Community Forum

I've written a simple non OS SDK test app and have confirmed I can't access any flash data address above 0x400000, no matter what value is in the upper 4 bits of byte[3] of flash. Makes me think the SDK (and possibly the ROM functions) don't actually support > 4MB access.

piersfinlayson wrote:I've written a simple non OS SDK test app and have confirmed I can't access any flash data address above 0x400000, no matter what value is in the upper 4 bits of byte[3] of flash. Makes me think the SDK (and possibly the ROM functions) don't actually support > 4MB access.

Must be missing something, I can't believe Wemos would build product with 16MB chips if we can't access >4MB

KevinA wrote:

piersfinlayson wrote:I've written a simple non OS SDK test app and have confirmed I can't access any flash data address above 0x400000, no matter what value is in the upper 4 bits of byte[3] of flash. Makes me think the SDK (and possibly the ROM functions) don't actually support > 4MB access.

Must be missing something, I can't believe Wemos would build product with 16MB chips if we can't access >4MB

It does seem unlikely doesn't it? I've asked on bbs.espressif.com.

I can't find any evidence on the internet anyone having successfully accessed >4MB flash from within the SDK. I have seem people who've added support to the flash tools and accessed the extra flash _externally_ - and I have this working fine. If anyone does have it working within the SDK (so from onboard the ESP8266) please let me know how!

Espressif have replied on their bbs and showed how to access the extra flash memory.

Essentially it seems like the byte[3] stored on the flash can't be used to indicate more than 4MB to the ROM or SDK. However, there's a structure flashchip(.chip_size) which stores the size in bytes of the flash chip, so if you modify that you can access the extra space.

Their example shows you wrapping the usual spi_flash functions with routines that stores off the original value of flashchip before your operation and then restores afterwards - so presumably the SDK will barf if you have flashchip.chip_size set to > 4MB.

I'll give this a go later.

Here's the thread with espressif:

http://bbs.espressif.com/viewtopic.php?f=7&t=2865