Looking at the existing scheme we use when defining a device's default parameters, there seem to be a slight variation of styles used -> comment style for default values, xx_CUSTOM vs. xx_BOARD vs. xx_DEFAULT...

Furthermore, we have a source of error in all of them: in case there is more than one device defined by a board (-> xx_BOARD has more than one entry), the SAUL reg info field has still only a single one. This leads to out-of-bound access to the SAUL info array during initialization...

So I propose to unify all default parameter files to the following scheme:

/**
 * @name   Default configuration parameters for device DEVX
 * @{
 */
#ifndef DEVX_PARAM_ABC
#define DEVX_PARAM_ABC ...
#endif
#ifndef DEVX_PARAM_TTT
#define DEVX_PARAM_TTT ...
#endif

#ifndef DEVX_PARAMS
#define DEVX_PARAMS       { .abc = DEVX_PARAM_ABC, \
                            .ttt = DEVX_PARAM_TTT }
#endif

#ifndef DEVX_SAULINFO
#define DEVX_SAULINFO      { .name = "devx" }
#endif
/** @} */

/**
 * @brief   DEVX configuration
 */
static const devx_params_t devx_params[] = {
    DEVX_PARAMS
};

/**
 * @brief   SAUL registry entires
 */
static const saul_reg_info_t devx_saul_reg_info[] = {
    DEVX_SAULINFO
};

This way, if a board or application can override the device config by re-defining the DEVX_PARAMS and DEVX_SAULINFO.

We can further add a check to the auto-init code, that makes sure that the number of defined devices and the number of defined SAUL infos matches:

#define INFO_NUM    (sizeof(devx_saul_reg_info) / sizeof(devx_saul_reg_info[0]))
#define PARAM_NUM   (sizeof(devx_params) / sizeof(devx_params[0]))
assert(INFO_NUM == PARAM_NUM);

What do you guys think about this?