git.defcon.no Git - avrfbosd/blob - render.c

   1 #include "render.h"
   2 #include <avr/io.h>
   3
   4
   5 extern volatile int buffer_position;
   6 extern volatile uint8_t hres_bytes;
   7 extern volatile char* screen_buffer;
   8
   9
  10 void asm_render_line( void ) {
  11                                 __asm__ __volatile__ (
  12         ".macro outbit p"               "\n\t"
  13                 "BST    __tmp_reg__,7"  "\n\t"  // Store bit 7 to T
  14                 "BLD    r16,7"          "\n\t"  // Load bit T into r16 bit number 7
  15                 "OUT    \\p,r16"        "\n\t"  // Send contents of r16 to %[port]
  16                 "NOP"                   "\n\t"  // Delay ...
  17                 "NOP"                   "\n\t"  // Delay ...
  18                 "NOP"                   "\n\t"  // Delay ...
  19         ".endm"                         "\n\t"
  20
  21                 "ADD    r26,r28"        "\n\t"  // Add register Y to register X, low part
  22                 "ADC    r27,r29"        "\n\t"  // Add high Y to X with carry from low part
  23
  24                 "IN     r16,%[port]"    "\n\t"  // Save port content to register 16
  25                 "RJMP   start_line"     "\n\t"
  26
  27         "loop_byte:"                    "\n\t"  // Notice that in the macro we always use bit 7 and left-shift
  28                 "BST    __tmp_reg__,6"  "\n\t"  // Here we use bit 6 without left-shift to output bit 0
  29                 "BLD    r16,7"          "\n\t"  // of each byte (except the last bit on the line)
  30                 "OUT    %[port],r16"    "\n\t"  // We do not have time for a left-shift, teh "extra cycle" was used for "dec-branch"
  31                 "NOP"                   "\n\t"  // Delay ...
  32                 "NOP"                   "\n\t"  // Delay ...
  33
  34         "start_line:"                   "\n\t"
  35                 "LD     __tmp_reg__,X+" "\n\t"  // Load from address pointed to by X into temporary register, then increment X-pointer
  36
  37                                 "outbit %[port]"        "\n\t"  // Output bit 7 using Macro
  38                 "LSL    __tmp_reg__"    "\n\t"  // Left-shift for next bit
  39                 "outbit %[port]"        "\n\t"  // Output bit 6 using Macro
  40                 "LSL    __tmp_reg__"    "\n\t"  // Left-shift for next bit
  41                 "outbit %[port]"        "\n\t"  // Output bit 5 using Macro
  42                 "LSL    __tmp_reg__"    "\n\t"  // Left-shift for next bit
  43                 "outbit %[port]"        "\n\t"  // Output bit 4 using Macro
  44                 "LSL    __tmp_reg__"    "\n\t"  // Left-shift for next bit
  45                 "outbit %[port]"        "\n\t"  // Output bit 3 using Macro
  46                 "LSL    __tmp_reg__"    "\n\t"  // Left-shift for next bit
  47                 "outbit %[port]"        "\n\t"  // Output bit 2 using Macro
  48                 "LSL    __tmp_reg__"    "\n\t"  // Left-shift for next bit
  49                 "outbit %[port]"        "\n\t"  // Output bit 1 using Macro
  50
  51                 "DEC    %[hr]"        "\n\t"  // Decrement num-bytes-remaining-in-resolution
  52                 "BRNE   loop_byte"      "\n\t"  // Branch to loop6 if %[hres] != zero
  53
  54                 "LSL    __tmp_reg__"    "\n\t"  // Left-shift for last bit on the line
  55                 "outbit %[port]"        "\n\t"  // Output bit 0 using Macro.
  56
  57                 "CBI    %[port],7"      "\n\t"  // Clear our "display bit" to ensure we end on black
  58
  59                 :
  60                 : [port] "i" (_SFR_IO_ADDR(PORTD)),
  61                 "x" (screen_buffer),
  62                 "y" (buffer_position),
  63                 [hr] "d" (hres_bytes)
  64                 : "r16"
  65                                 );
  66 }