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Arduboy2
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Refactor and optimise paintScreen() in assembler 

By @MrBlinky with contributions from @veritazz (Michael Gollnick) and
@MLXXXp (Scott Allen).
This commit is contained in:
Mr.Blinky 2018-01-18 09:39:25 -05:00 committed by Scott Allen
parent d44b89e01f
commit bd726fc112
1 changed files with 34 additions and 0 deletions
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34
src/Arduboy2Core.cpp
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@ -313,6 +313,39 @@ void Arduboy2Core::paintScreen(const uint8_t *image)
// paint from a memory buffer, this should be FAST as it's likely what // paint from a memory buffer, this should be FAST as it's likely what
// will be used by any buffer based subclass // will be used by any buffer based subclass
//
// The following assembly code runs "open loop". It relies on instruction
// execution times to allow time for each byte of data to be clocked out.
// It is specifically tuned for a 16MHz CPU clock and SPI clocking at 8MHz.
void Arduboy2Core::paintScreen(uint8_t image[], bool clear)
{
uint16_t count;
asm volatile (
" ldi %A[count], %[len_lsb] \n\t" //for (len = WIDTH * HEIGHT / 8)
" ldi %B[count], %[len_msb] \n\t"
"1: ld __tmp_reg__, %a[ptr] ;2 \n\t" //tmp = *(image)
" out %[spdr], __tmp_reg__ ;1 \n\t" //SPDR = tmp
" cpse %[clear], __zero_reg__ ;1/2 \n\t" //if (clear) tmp = 0;
" mov __tmp_reg__, __zero_reg__ ;1 \n\t"
"2: sbiw %A[count], 1 ;2 \n\t" //len --
" sbrc %A[count], 0 ;1/2 \n\t" //loop twice for cheap delay
" rjmp 2b ;2 \n\t"
" st %a[ptr]+, __tmp_reg__ ;2 \n\t" //*(image++) = tmp
" brne 1b ;1/2 :18 \n\t" //len > 0
" in __tmp_reg__, %[spsr] \n\t" //read SPSR to clear SPIF
: [ptr] "+&e" (image),
[count] "=&w" (count)
: [spdr] "I" (_SFR_IO_ADDR(SPDR)),
[spsr] "I" (_SFR_IO_ADDR(SPSR)),
[len_msb] "M" (WIDTH * (HEIGHT / 8 * 2) >> 8), // 8: pixels per byte
[len_lsb] "M" (WIDTH * (HEIGHT / 8 * 2) & 0xFF), // 2: for delay loop multiplier
[clear] "r" (clear)
);
}
#if 0
// For reference, this is the "closed loop" C++ version of paintScreen()
// used prior to the above version.
void Arduboy2Core::paintScreen(uint8_t image[], bool clear) void Arduboy2Core::paintScreen(uint8_t image[], bool clear)
{ {
uint8_t c; uint8_t c;
@ -349,6 +382,7 @@ void Arduboy2Core::paintScreen(uint8_t image[], bool clear)
} }
while (!(SPSR & _BV(SPIF))) { } // wait for the last byte to be sent while (!(SPSR & _BV(SPIF))) { } // wait for the last byte to be sent
} }
#endif
void Arduboy2Core::blank() void Arduboy2Core::blank()
{ {