ra8_epaper_devinfo.c

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#include <stddef.h>
#include <stdint.h>
 
#include "ra8_attributes.h"
#include "ra8_check.h"
#include "ra8_epaper.h"
#include "ra8_err.h"

static const char* const s_tag = "EPAPER";

typedef enum : uint8_t {
  k_ra8_epaper_di_byte_mask    = 0xFFU, 
  k_ra8_epaper_di_byte_shift   = 8U,    
  k_ra8_epaper_di_word_shift   = 16U,   
  k_ra8_epaper_di_ver_per_word = 2U,    
  k_ra8_epaper_di_ascii_min    = 0x20U, 
  k_ra8_epaper_di_ascii_max    = 0x7FU, 
} ra8_epaper_devinfo_const_t;

typedef enum : uint8_t {
  k_ra8_epaper_di_idx_width  = 0U,  
  k_ra8_epaper_di_idx_height = 1U,  
  k_ra8_epaper_di_idx_buf_lo = 2U,  
  k_ra8_epaper_di_idx_buf_hi = 3U,  
  k_ra8_epaper_di_idx_fw     = 4U,  
  k_ra8_epaper_di_idx_lut    = 12U, 
  k_ra8_epaper_di_idx_end    = 20U, 
} ra8_epaper_devinfo_idx_t;

RA8_INTERNAL
static void internal_ra8_epaper_unpack_ver_word(uint16_t word, char* dst)
{
  const uint8_t hi =
    (uint8_t)((word >> (uint16_t)k_ra8_epaper_di_byte_shift) & (uint16_t)k_ra8_epaper_di_byte_mask);
  const uint8_t lo = (uint8_t)(word & (uint16_t)k_ra8_epaper_di_byte_mask);
  const bool    hi_p =
    (hi >= (uint8_t)k_ra8_epaper_di_ascii_min) && (hi < (uint8_t)k_ra8_epaper_di_ascii_max);
  const bool lo_p =
    (lo >= (uint8_t)k_ra8_epaper_di_ascii_min) && (lo < (uint8_t)k_ra8_epaper_di_ascii_max);
  /* Cast the whole conditional, not each arm: the usual arithmetic
   * conversions give the ternary type `int`, so casting only the value arm
   * still leaves an implicit int -> char narrowing at the assignment. Both
   * arms are bounded by the printable-ASCII test above (0x20 .. 0x7E), so
   * every value is representable in a signed char. */
  dst[0] = (char)(hi_p ? hi : 0U);
  dst[1] = (char)(lo_p ? lo : 0U);
}

RA8_INTERNAL
static void
internal_ra8_epaper_decode_dev_word(uint32_t idx, uint16_t word, ra8_epaper_dev_info_t* out)
{
  if (idx == (uint32_t)k_ra8_epaper_di_idx_width) {
    out->panel_width = word;
  } else if (idx == (uint32_t)k_ra8_epaper_di_idx_height) {
    out->panel_height = word;
  } else if (idx == (uint32_t)k_ra8_epaper_di_idx_buf_lo) {
    out->image_buf_base |= (uint32_t)word;
  } else if (idx == (uint32_t)k_ra8_epaper_di_idx_buf_hi) {
    out->image_buf_base |= ((uint32_t)word << (uint32_t)k_ra8_epaper_di_word_shift);
  } else if (idx < (uint32_t)k_ra8_epaper_di_idx_lut) {
    const uint32_t off =
      (idx - (uint32_t)k_ra8_epaper_di_idx_fw) * (uint32_t)k_ra8_epaper_di_ver_per_word;
    internal_ra8_epaper_unpack_ver_word(word, &out->fw_version[off]);
  } else {
    const uint32_t off =
      (idx - (uint32_t)k_ra8_epaper_di_idx_lut) * (uint32_t)k_ra8_epaper_di_ver_per_word;
    internal_ra8_epaper_unpack_ver_word(word, &out->lut_version[off]);
  }
}
 
[[nodiscard]] ra8_err_t
ra8_epaper_decode_dev_info(const uint16_t* words, size_t count, ra8_epaper_dev_info_t* out_info)
{
  RA8_CHECK_NULL_PTR(words, s_tag, "decode_dev_info: words null");
  RA8_CHECK_NULL_PTR(out_info, s_tag, "decode_dev_info: out null");
  if (count < (size_t)k_ra8_epaper_di_idx_end) {
    ra8_log_error(s_tag, "decode_dev_info: short response");
    return k_ra8_err_invalid_arg;
  }
 
  *out_info = (ra8_epaper_dev_info_t){};
  for (uint32_t i = 0U; i < (uint32_t)k_ra8_epaper_di_idx_end; i++) {
    internal_ra8_epaper_decode_dev_word(i, words[i], out_info);
  }
  /* The version fields are one char longer than the packed data, so the
   * terminator lands past the last decoded char and can never be
   * overwritten by the loop above. */
  out_info->fw_version[k_ra8_epaper_ver_chars]  = '\0';
  out_info->lut_version[k_ra8_epaper_ver_chars] = '\0';
  return k_ra8_ok;
}