Use linker to relocate const PALConfig pal_default_config to RAM

[andresv]

I would like to do a little hack. Basically I would like to choose between 2 different PALConfigs without modifying ChibiOS.
There is those lines in hal.c

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void halInit() {
   ...
    palInit(&pal_default_config);
   ...
}

Where pal_default_config is defined in
board.c file as

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const PALConfig pal_default_config = {...

and in hal_pal_lld.h as

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extern const PALConfig pal_default_config;

My idea is to modify pal_default_config in main.c before calling halInit(). So basically some conf is readout from flash which tells if one particular pin should be defined LOW or HIGH during palInit(1). Something like this in main.c:

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stm32_gpio_setup_t portb = {VAL_GPIOB_MODER, VAL_GPIOB_OTYPER, VAL_GPIOB_OSPEEDR, VAL_GPIOB_PUPDR, VAL_GPIOB_ODR | 0x01,  VAL_GPIOB_AFRL, VAL_GPIOB_AFRH};
PALConfig* config = (PALConfig*)&pal_default_config; // do not use const qualifier
if (conf == 1) {
    memcpy(&config->PBData, &portb, sizeof(stm32_gpio_setup_t));
}
halInit();
chSysInit();


It works fine if I modify const PALConfig pal_default_config (hal_pal_lld.h and board.c) to be not const. But I would prefer if hal_pal_lld.h is not touched, however it is ok to modify board.c file.

What I tried to do was to modify where this variable is linked. So I came up with this in board.c.

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const PALConfig pal_default_config __attribute__((section(".ram0"))) = {

But I guess section name should be something different or I have to actually modify .ld file to accomplish this.
I am using STM32F030x8

Current .ld is something like that (I remember that old ld scripts were different):

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/*
 * STM32F030x8 memory setup.
 */
MEMORY
{
    flash   : org = 0x08000000, len = 28k
    newapp  : org = 0x08009000, len = 28k
    ram0    : org = 0x20000000, len = 8k
    ram1    : org = 0x00000000, len = 0
    ram2    : org = 0x00000000, len = 0
    ram3    : org = 0x00000000, len = 0
    ram4    : org = 0x00000000, len = 0
    ram5    : org = 0x00000000, len = 0
    ram6    : org = 0x00000000, len = 0
    ram7    : org = 0x00000000, len = 0
}

/* For each data/text section two region are defined, a virtual region
   and a load region (_LMA suffix).*/

/* Flash region to be used for exception vectors.*/
REGION_ALIAS("VECTORS_FLASH", flash);
REGION_ALIAS("VECTORS_FLASH_LMA", flash);

/* Flash region to be used for constructors and destructors.*/
REGION_ALIAS("XTORS_FLASH", flash);
REGION_ALIAS("XTORS_FLASH_LMA", flash);

/* Flash region to be used for code text.*/
REGION_ALIAS("TEXT_FLASH", flash);
REGION_ALIAS("TEXT_FLASH_LMA", flash);
...


In short, how pal_default_config must be defined in board.c and what should be modified in .ld file to accomplish this.

[Giovanni]

Hi,

I can't see an easy way to do that.

One of the next changes to HAL is to move the board stuff out of the PAL driver and have board.c include everything, you may just wait that the change is done. Anyway, this is the current direction: remove the dependency, in the meanwhile a little hack in the code would not hurt.

Giovanni

[andresv]

Ok, I think that messing with liker is actually nice hack, however there is something wrong with my current approach. Probably

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const PALConfig pal_default_config __attribute__((section(".ram0"))) = {...

must be defined differently or some more info must be added to .ld file, but currently I do not know what exactly.

[apmorton]

A dirty trick I have used to accomplish a similar goal is to skip initialization of pal_default_config entirely.
GCC will then drop it into the BSS segment even though it is defined as const - although note this may be on the edge of defined behavior, and may be subject to certain compiler optimizations/options being enabled.

in board.c you could do this:

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const PALConfig pal_default_config;
const PALConfig pal_default_config_real = {
   ...
};


in main.c you then do this:

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memcpy((PALConfig*)&pal_default_config, &pal_default_config_real, sizeof(pal_default_config));

halInit();
chSysInit();


Your approach would also work, but you are using the wrong value for the section attribute.

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const PALConfig pal_default_config __attribute__((section(".data")))


[andresv]

Nice one, thanks a lot.