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Speed up AVR Software SPI routine #127

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Speed up AVR Software SPI routine #127

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90 changes: 71 additions & 19 deletions cppsrc/Ucglib.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -115,33 +115,85 @@ static void ucg_com_arduino_init_shift_out(uint8_t dataPin, uint8_t clockPin)
u8g_bitNotData ^= 0x0ff;
}

// This assembler macro takes 5 clock cycles, regardless of whether
// "bit" in "val" is set or cleared.
#define SPI_BIT(val, bit, dat0, dat1, outData) \
__asm__ __volatile__("mov __tmp_reg__,%2" "\n\t" \
"sbrc %0,%1" "\n\t" \
"mov __tmp_reg__,%3" "\n\t" \
"st %a4,__tmp_reg__" "\n\t" \
: /* No outputs */ \
: "r" (val), "I" (bit), \
"r" (dat0), "r" (dat1), \
"e" (outData) \
)

static void ucg_com_arduino_send_generic_SW_SPI(ucg_t *ucg, uint8_t val) UCG_NOINLINE;
static void ucg_com_arduino_send_generic_SW_SPI(ucg_t *ucg, uint8_t val)
{
uint8_t cnt = 8;
uint8_t bitData = u8g_bitData;
uint8_t bitNotData = u8g_bitNotData;
uint8_t bitClock = u8g_bitClock;
uint8_t bitNotClock = u8g_bitNotClock;
volatile uint8_t *outData = u8g_outData;
volatile uint8_t *outData = u8g_outData;
volatile uint8_t *outClock = u8g_outClock;

UCG_ATOMIC_START();
do
{
if ( val & 128 )
*outData |= bitData;
else
*outData &= bitNotData;

if (outData == outClock) {
// If outData and outClock are pointing to the same port,
// then we can set both clock and data bits with one write.

// 10 clock cycles to set up registers
uint8_t dat0_clk0 = *outData & u8g_bitNotClock & u8g_bitNotData;
uint8_t dat0_clk1 = dat0_clk0 | u8g_bitClock;
uint8_t dat1_clk0 = dat0_clk0 | u8g_bitData;
uint8_t dat1_clk1 = dat0_clk1 | u8g_bitData;

// 10 clock cycles per bit = 1.6 MHz bit time for Arduino Uno
// Data changes on the falling edge of the clock for 50% setup/hold
SPI_BIT(val, 7, dat0_clk0, dat1_clk0, outData);
SPI_BIT(val, 7, dat0_clk1, dat1_clk1, outData);

SPI_BIT(val, 6, dat0_clk0, dat1_clk0, outData);
SPI_BIT(val, 6, dat0_clk1, dat1_clk1, outData);

SPI_BIT(val, 5, dat0_clk0, dat1_clk0, outData);
SPI_BIT(val, 5, dat0_clk1, dat1_clk1, outData);

SPI_BIT(val, 4, dat0_clk0, dat1_clk0, outData);
SPI_BIT(val, 4, dat0_clk1, dat1_clk1, outData);

SPI_BIT(val, 3, dat0_clk0, dat1_clk0, outData);
SPI_BIT(val, 3, dat0_clk1, dat1_clk1, outData);

SPI_BIT(val, 2, dat0_clk0, dat1_clk0, outData);
SPI_BIT(val, 2, dat0_clk1, dat1_clk1, outData);

SPI_BIT(val, 1, dat0_clk0, dat1_clk0, outData);
SPI_BIT(val, 1, dat0_clk1, dat1_clk1, outData);

SPI_BIT(val, 0, dat0_clk0, dat1_clk0, outData);
SPI_BIT(val, 0, dat0_clk1, dat1_clk1, outData);

//*outClock &= u8g_bitNotClock; // Only necessary if clock needs to be low after byte transfer
} else {
uint8_t cnt = 8;
uint8_t bitData = u8g_bitData;
uint8_t bitNotData = u8g_bitNotData;
uint8_t bitClock = u8g_bitClock;
uint8_t bitNotClock = u8g_bitNotClock;

do
{
if ( val & 128 )
*outData |= bitData;
else
*outData &= bitNotData;

*outClock |= bitClock;
val <<= 1;
cnt--;
*outClock &= bitNotClock;
} while( cnt != 0 );
UCG_ATOMIC_END();

*outClock |= bitClock;
val <<= 1;
cnt--;
*outClock &= bitNotClock;
} while( cnt != 0 );
}
UCG_ATOMIC_END();
}

#else
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