diff options
| -rw-r--r-- | libraries/SPI/SPI.h | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/libraries/SPI/SPI.h b/libraries/SPI/SPI.h index b54e2df..24ebc12 100644 --- a/libraries/SPI/SPI.h +++ b/libraries/SPI/SPI.h @@ -184,6 +184,12 @@ public: // Write to the SPI bus (MOSI pin) and also receive (MISO pin) inline static uint8_t transfer(uint8_t data) { SPDR = data; + /* + * The following NOP introduces a small delay that can prevent the wait + * loop form iterating when running at the maximum speed. This gives + * about 10% more speed, even if it seems counter-intuitive. At lower + * speeds it is unnoticed. + */ asm volatile("nop"); while (!(SPSR & _BV(SPIF))) ; // wait return SPDR; @@ -193,16 +199,20 @@ public: in.val = data; if (!(SPCR & _BV(DORD))) { SPDR = in.msb; + asm volatile("nop"); // See transfer(uint8_t) function while (!(SPSR & _BV(SPIF))) ; out.msb = SPDR; SPDR = in.lsb; + asm volatile("nop"); while (!(SPSR & _BV(SPIF))) ; out.lsb = SPDR; } else { SPDR = in.lsb; + asm volatile("nop"); while (!(SPSR & _BV(SPIF))) ; out.lsb = SPDR; SPDR = in.msb; + asm volatile("nop"); while (!(SPSR & _BV(SPIF))) ; out.msb = SPDR; } |