FAQ – Lehrstuhl für Informatik 4

libspicboard
 #ifndef _DISPLAY_H
 #define _DISPLAY_H
  
 #include <stdint.h>
 #ifdef _AVR_LIBC_VERSION__
 #include <avr/pgmspace.h>
 #endif
 #include "check.h"
  
 /**
  * \addtogroup Display OLED Display
  *
  * \brief Controls the optional 128×64 pixel monochrome OLED display
  *
  * The SPiCboard v3 has a TWI (two wire interface, also known as I²C),
  * which can be used to connect an OLED display.
  * Especially the SSD1306 monochrome OLED display fits perfectly onto the board.
  * It has a 0.96 inch diameter with 128 horizontal and 64 vertical pixels.
  *
  * For the sake of simplicity the horizontal pixels are termed <i>columns</i>.
  * The vertical pixels are divided into 8 so-called <i>pages</i>, therefore
  * a byte can represent the contents of a <i>page segment</i> (with 8 pixels - from
  * the <a href="https://en.wikipedia.org/wiki/Least_significant_bit">LSB</a> on
  * top to the <a href="https://en.wikipedia.org/wiki/Most_significant_bit">MSB</a>
  * on bottom of each page segement).
  *
  * \image html display_addr.png
  *
  * For additional details please have a look into the <a href="SSD1306.pdf">SSD1306 Datasheet</a>.
  *
  * In case your run into memory issues (which is quite easy with only 2 KB SRAM)
  * you might want to have a look into the \ref DisplayFromFlash "FromFlash" function variants.
  *
  * \warning The display is quite sensitive to fluctuation of current.
  *          Try to avoid contact of any [semi-]conductive material (including your fingers) with the pins
  *          on the Xplained Mini Board -- especially connecting PC3 with PC4 -- or the connection to your display
  *          might stop (it stalls until you restart it, the LED on the Xplained Mini Board can indicate the error).
  *
  * @{
  * \file display.h
  * \version \$Rev:  $
  */
  
 /**
  * \brief Activate (and setup) the OLED-display
  *
  * \retval  0  success
  * \retval -1  initialization of I²C failed
  * \retval -2  setting I²C device address failed
  * \retval -3  writing to I²C device failed
  * \retval -4  timeout during I²C communication
  * \retval -5  out of bounds (addressing nonexistent page/column)
  */
 int8_t sb_display_enable();
  
 /**
  * \brief Check if a functional OLED display is present
  *
  * Tries to connect to the SSD1306 display (I²C device address <tt>0x78</tt>)
  * without enabling it.
  *
  * \retval 0   display is available and seems to work
  * \retval <0  display not available or not functional
  */
 int8_t sb_display_available();
  
 /**
  * \brief Turn the OLED display off
  *
  * \retval 0   success
  * \retval <0  on I²C error (\see sb_display_enable() return codes)
  */
 int8_t sb_display_disable();
  
 /**
  * \brief Draw a single page segment onto the OLED display
  *
  * \param pageNum  page number (0-7) for vertical positioning the output
  * \param colNum   column number (0-127) for the horizontal position of the output
  * \param content  contents to be drawn on the page segment (LSB on top and MSB on bottom)
  *
  * \retval 0   success
  * \retval <0  on I²C error (\see sb_display_enable() return codes)
  */
 int8_t sb_display_draw(uint8_t pageNum, uint8_t colNum, uint8_t content);
  
 /**
  * \brief Draw a (rectangular) bitmap onto the OLED display
  *
  * The result is similar to multiple calls of sb_display_draw()
  * (although the execution of this function is way faster):
  * \code {.c}
  *  for (uint8_t page = 0; page < pageCount; page++){
  *      for (uint8_t col = 0; col < colCount; col++){
  *          sb_display_draw(pageStart + page, colStart + col, contents[page * colCount + col]);
  *      }
  * }
  * \endcode
  *
  * \b Example:
  *
  * We want to draw a square with a point in its center with some spacing
  * to the to the left top corner of the screen.
  *
  * The bitmap will be drawn across two pages, each with eight page segments.
  * \image html display_square.png
  *
  * Hence we first initialize an array with 2*8 elements (columns 5-12 for
  * page 0 and 1) containing the contents of each page segement (1 for a white
  * pixel and 0 for a black/clear one) and then transfer them to the screen.
  * \include display_square.c
  *
  * \param pageStart  first page to set the top vertical position
  * \param colStart   first column to set the left horizontal position
  * \param pageCount  number of pages to set the bottom position
  *                   (including the first page)
  * \param colCount   number of columns to define the right border
  *                   (including the first column)
  * \param contents   array pointing to the bitmap (must have
  *                   <tt>pageCount * colCount</tt> elements) - or \c NULL
  *                   to clear the area
  *
  * \retval 0   success
  * \retval <0  on I²C error (see sb_display_enable() return codes)
  */
 int8_t sb_display_drawBitmap(uint8_t pageStart, uint8_t colStart, uint8_t pageCount, uint8_t colCount, const uint8_t * contents);
  
 /**
  * \brief Draw the contents of a \c 8*128 item 8-bit array (8 pages with
  *        128 columns, each filled with 8 bit) onto the OLED Display
  *
  * The function call is identical to
  * \code {.c}
  *  sb_display_drawBitmap(0, 0, 8, 128, contents);
  * \endcode
  *
  * In case the pointer is \c NULL, the entire screen will be cleared.
  *
  * \warning Make sure that the buffer points to an array with 1024 items -
  *          this is C, there is no range check!
  *
  * \param contents  pointer to a <tt>8*128</tt> item array - or NULL
  *                  to clear the screen
  *
  * \retval  0  success
  * \retval  <0 on I²C error (\see sb_display_enable() return codes)
  */
 int8_t sb_display_fillScreen(const uint8_t *contents);
  
 /**
  * \brief Print a \c \0 terminated text string on the OLED display
  *        using a 8×8 pixel font
  *
  * A single character will fit into one page (= eight rows) and eight columns.
  * Therefore it is possible to print 16 characters at maximum.
  *
  * If the length of the string exceeds the available columns
  * (= columns right of the start column) in the current page,
  * the output will \b not be continued on the next line!
  *
  * The font was extract from the
  * <a href="https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/lib/fonts">Linux kernel</a>
  * and is based on <a href="https://en.wikipedia.org/wiki/Code_page_437">code page 437</a>
  * (= <a href="https://en.wikipedia.org/wiki/Extended_ASCII">extended ASCII</a>,
  * every possible character has a graphical string representation).
  *
  * Consequently, the ASCII control characters (like line break) are
  * displayed with special symbols but don't have any functional impact.
  *
  * The \ref fonts "Fonts Table" contains a detailed list of the available characters
  *
  * \warning The font will be stored on the flash which will consume about 2300 bytes.
  *
  * \param pageNum   page number (0-7) for vertical positioning the output
  * \param colStart  first column to set the horizontal position of the output
  * \param str       0-terminated string
  *
  * \retval >=0  length of printed string (can be less than strlen(str) )
  * \retval <0   on I²C error (\see sb_display_enable() return codes)
  */
 int8_t sb_display_showString(uint8_t pageNum, uint8_t colStart, const char *str);
  
 /**
  * \brief Print a \c \0 terminated text string with a (slightly) wider
  *        8×8 pixel font onto the OLED display
  *
  * The character set is almost identical to the sb_display_showString() function
  * and the space requirement is the same (up to 16 characters per line)
  *
  * The \ref fonts "Fonts Table" contains a detailed list of the
  * available characters.
  *
  * \warning This font will consume about 2300 bytes, too.
  *
  * \param pageNum   page number (0-7) for vertical positioning the output
  * \param colStart  first column to set the horizontal position of the output
  * \param str       0-terminated string
  *
  * \retval >=0  length of printed string (can be less than strlen(str) )
  * \retval <0   on I²C error (see sb_display_enable() return codes)
  */
 int8_t sb_display_showStringWide(uint8_t pageNum, uint8_t colStart, const char *str);
  
 /**
  * \brief Print a \0 terminated text string on the OLED display using
  *        a small 6×4 pixel font
  *
  * A single character will fit into one page (eight rows, even though it is
  * just six pixels) and four columns, therefore it is possible to print 32
  * characters at maximum.
  *
  * If the length of the string exceeds the available columns
  * (= columns right of the start column) in the current page,
  * the output will not be continued on the next line!
  *
  * The \ref fonts "Fonts Table" contains a detailed list of the
  * available characters
  *
  * \warning In contrast to the other \c showString functions the character set
  *          is quite limited - it only supports printable ASCII characters (neither
  *          control characters nor the extended ASCII set).
  *          Hence, the required flash memory consumption is (with about 700 bytes) less
  *          than a third of the space requirements of the other fonts.
  *
  * \param pageNum   page number (0-7) for vertical positioning the output
  * \param colStart  first column to set the horizontal position of the output
  * \param str       0-terminated string
  *
  * \retval >=0  length of printed string (can be less than strlen(str) )
  * \retval <0   on I²C error (\see sb_display_enable() return codes)
  */
 int8_t sb_display_showStringSmall(uint8_t pageNum, uint8_t colStart, const char * str);
  
 /** @}*/
  
 /**
  * \addtogroup DisplayFromFlash Display contents from Flash memory
  *
  * \brief Display functions enabling flash memory contents
  *
  * For microcontroller-based software development, memory usage is a crucial part.
  * The SRAM on the Atmega 328PB (the processor of the Xplained Mini / SPiCboard v3)
  * is extremly tight compared to PCs -- its 2 KB are the limiting factor for
  * using the 128×64 pixel monochrome OLED display:
  * Just the contents of a single screen (128×64 bits) would consume half of
  * the available SRAM!
  *
  * But since most data is constant, this can be stored and read from the flash
  * program memory (with 32 KB on this microprocessor it is sixteen times the SRAM).
  *
  * Due to the different address space, it is not possible to access the data in flash
  * in the same way you access SRAM contents -- a special instruction is required to
  * read from this memory: the \c ldm instruction (instead of \c ld).
  *
  * This will be done automatically by the compiler when using the
  * <a href="https://gcc.gnu.org/onlinedocs/gcc-4.8.0/gcc/Named-Address-Spaces.html">Named-Address-Space</a>
  * keyword \c __flash in the variable declaration.
  *
  * In case you have quite an old compiler not supporting this feature,
  * you have to use the <a href="http://www.nongnu.org/avr-libc/user-manual/group__avr__pgmspace.html">Program Space Utilities</a>
  * from the <a href="http://www.nongnu.org/avr-libc/">AVR LibC</a>
  * and not only tag the variables with the \c PROGMEM keywords but although use the \c pgm_read_byte function to access them.
  *
  * The following functions use the same parameters (besides the \c flash keyword)
  * as their counter parts and their function name is appended by \c FromFlash
  *
  * @{
  * \file display.h
  * \version \$Rev:  $
  */
  
  /**
  * \brief Draw a bitmap from the flash memory onto the OLED display
  *
  * Almost the same function as sb_display_drawBitmap(), but the contents are
  * read from the flash (program memory) - so no SRAM is wasted.
  *
  * \see sb_display_drawBitmap
  *
  * \param pageStart  first page to set the top vertical position
  * \param colStart   first column to set the left horizontal position
  * \param pageCount  number of pages to set the bottom position
  * \param colCount   number of columns to define the right border
  * \param contents   array (<tt>pageCount * colCount</tt> elements) pointing to a bitmap
  *                   stored in the flash memory (using either
  *                   <a href="https://gcc.gnu.org/onlinedocs/gcc-5.4.0/gcc/Named-Address-Spaces.html">__flash</a>
  *                   namespace or <a href="http://www.nongnu.org/avr-libc/user-manual/pgmspace.html">PROGMEM</a> macro)
  *
  * \retval 0   success
  * \retval <0  on I²C error (see sb_display_enable() return codes)
  */
 #ifdef __FLASH
 int8_t sb_display_drawBitmapFromFlash(uint8_t pageStart, uint8_t colStart, uint8_t pageCount, uint8_t colCount, const __flash uint8_t *contents);
 #else
 int8_t sb_display_drawBitmapFromFlash(uint8_t pageStart, uint8_t colStart, uint8_t pageCount, uint8_t colCount, const uint8_t * PROGMEM contents);
 #endif
  
 /**
  * \brief Draw the contents of the flash to the entire OLED display screen
  *
  * Almost same function as sb_display_fillScreen(), but the contents are
  * read from the flash (program memory) - so no SRAM is wasted.
  *
  * The function call is identical to
  * \code {.c}
  *  sb_display_drawBitmapFromFlash(0, 0, 8, 128, contents);
  * \endcode
  *
  * \param contents  pointer to a \c 8*128 item array in flash memory (using either
  *                  <a href="https://gcc.gnu.org/onlinedocs/gcc-5.4.0/gcc/Named-Address-Spaces.html">__flash</a>
  *                  namespace or <a href="http://www.nongnu.org/avr-libc/user-manual/pgmspace.html">PROGMEM</a> macro)
  *
  * \retval 0   success
  * \retval <0  on I²C error (see sb_display_enable() return codes)
  */
 #ifdef __FLASH
 int8_t sb_display_fillScreenFromFlash(const __flash uint8_t *contents);
 #else
 int8_t sb_display_fillScreenFromFlash(const uint8_t * PROGMEM contents);
 #endif
  
 /**
  * \brief Print a \c \0 terminated text string from flash
  *        on the OLED display using a 8×8 pixel font
  *
  * Almost same function as sb_display_showString(), but the string is
  * read from the flash (program memory) - so no SRAM is wasted.
  *
  * The \ref fonts "Fonts Table" contains a detailed list of the available characters
  *
  * It is possible to define an inline flash string using the \c PSTR macro from the
  * <a href="http://www.nongnu.org/avr-libc/user-manual/pgmspace.html">Program Space Utilities</a>:
  * \code {.c}
  * static const __flash str[] = "Ipsum";
  *  sb_display_showString(0, 0, "Lorem");
  *  sb_display_showStringFromFlash(1, 0, str);
  *  sb_display_showStringFromFlash(2, 0, PSTR("dolor"));
  * \endcode
  * This will display \a Lorem , \a Ipsum and \a dolor on the subsequent lines,
  * but only the first string will consume SRAM during runtime.
  * The second and third call are different ways for reading from flash memory.
  *
  * \warning The font will be stored on the flash which will consume about 2300 bytes
  *          (but there is no additional overhead in case you are already
  *          using the sb_display_showString() ).
  *
  * \param pageNum   page number (0-7) for vertical positioning the output
  * \param colStart  first column to set the horizontal position of the output
  * \param str       0-terminated string in flash memory
  *
  * \retval >=0  length of printed string (can be less than strlen(str) )
  * \retval <0   on I²C error (\see sb_display_enable() return codes)
  */
 #ifdef __FLASH
 int8_t sb_display_showStringFromFlash(uint8_t pageNum, uint8_t colStart, const __flash char *str);
 #else
 int8_t sb_display_showStringFromFlash(uint8_t pageNum, uint8_t colStart, const char * PROGMEM str);
 #endif
  
 /**
  * \brief Print a \c \0 terminated text string from flash
  *        with a (slightly) wider 8×8 pixel font onto the OLED display
  *
  * Almost same function as sb_display_showStringWide(), but the string is
  * read from the flash (program memory) - so no SRAM is wasted.
  *
  * The \ref fonts "Fonts Table" contains a detailed list of the
  * available characters.
  *
  * \warning This font will consume about 2300 bytes, too (but no additional
  *          overhead for using sb_display_showStringWide() ).
  *
  * \param pageNum   page number (0-7) for vertical positioning the output
  * \param colStart  first column to set the horizontal position of the output
  * \param str       0-terminated string in flash memory
  *
  * \retval >=0  length of printed string (can be less than strlen(str) )
  * \retval <0   on I²C error (see sb_display_enable() return codes)
  */
 #ifdef __FLASH
 int8_t sb_display_showStringWideFromFlash(uint8_t pageNum, uint8_t colStart, const __flash char *str);
 #else
 int8_t sb_display_showStringWideFromFlash(uint8_t pageNum, uint8_t colStart, const char * PROGMEM str);
 #endif
  
 /**
  * \brief Print a \0 terminated text string from flash
  *        on the OLED display using a small 6×4 pixel font
  *
  * Almost same function as sb_display_showStringSmall(), but the string is
  * read from the flash (program memory) - so no SRAM is wasted.
  *
  * The \ref fonts "Fonts Table" contains a detailed list of the
  * available characters
  *
  * \warning This font will consume about 700 bytes (but no additional
  *          overhead for using sb_display_showStringSmall() ).
  *
  * \param pageNum   page number (0-7) for vertical positioning the output
  * \param colStart  first column to set the horizontal position of the output
  * \param str       0-terminated string from flash
  *
  * \retval >=0  length of printed string (can be less than strlen(str) )
  * \retval <0   on I²C error (\see sb_display_enable() return codes)
  */
 #ifdef __FLASH
 int8_t sb_display_showStringSmallFromFlash(uint8_t pageNum, uint8_t colStart, const __flash char *str);
 #else
 int8_t sb_display_showStringSmallFromFlash(uint8_t pageNum, uint8_t colStart, const char * PROGMEM str);
 #endif
  
 /** @}*/
  
 #endif
  