Data access on SFLASH (ICACHE_RODATA_ATTR)

[narayan]

Hi -
I am trying to use the ICACHE_FLASH_ATTR (to put data tables into
the SFLASH).

There are a couple of problems that I have:

1. I cannot access variables here (Read only) as a character array - Only integer access
seems to be allowed.
2. Often times when I merely have this in my code (even when not executing). The
system will not boot.

I saw only one example of ICACHE_RODATA_ATTR being used in lwip (for ip_addr_any).
I noticed that your memory alloc (debug version) uses this sometimes
Questions:
1. Have you tested this ability to put RO data into flash
2. What are the restrictions (Address, access, alignment) etc.
I am aware this is how your code that resides on flash works (through some cache refresh mechanism).
Does data not work the same way?

Thanks in advance for your help

Narayan

[ESP_Faye]

Hi,

To put the array into flash, you can define it as below, otherwise it will be stored in ram.

Code: Select all

static const char XXXX[] ICACHE_RODATA_ATTR = { ........ }

Please notice that the flash read/write has to be 4 bytes aligned, so it has to be as type uint32.

Thanks for your interest in ESP8266 !

[gustavomassa]

Hello, I would like to understand the os_printf:

/* NOTE: don't use printf_opt in irq handler, for test */
#define os_printf(fmt, ...) do { \
static const char flash_str[] ICACHE_RODATA_ATTR STORE_ATTR = fmt; \
printf(flash_str, ##__VA_ARGS__); \
} while(0)
Where inside the flash the variable flash_str is being saved? What address?
If I use the same logic to save another string into the flash:
static const char flashString[] ICACHE_RODATA_ATTR STORE_ATTR = "TEST";
How can I read the flashString variable? If I read it directly it results in a fatal exception(3).
I can copy the content of the flashString to another buffer using memcpy, but I would like to read it directly without memcpy.