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Code Issues Wiki Activity

DSHOT/Bitbang - Hold the line at idle for 1 extra bit period.

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This commit is contained in:
Dominic Clifton 2022-03-12 12:04:38 +01:00
parent e88df3bb68
commit 25023bb3a2
2 changed files with 22 additions and 6 deletions
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24
src/main/drivers/dshot_bitbang.c
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@ -145,13 +145,27 @@ static void bbOutputDataInit(uint32_t *buffer, uint16_t portMask, bool inverted)
setMask = portMask;
}
int bitpos;
int symbol_index;
for (bitpos = 0; bitpos < 16; bitpos++) {
buffer[bitpos * 3 + 0] |= setMask ; // Always set all ports
buffer[bitpos * 3 + 1] = 0; // Reset bits are port dependent
buffer[bitpos * 3 + 2] |= resetMask; // Always reset all ports
for (symbol_index = 0; symbol_index < MOTOR_DSHOT_FRAME_BITS; symbol_index++) {
buffer[symbol_index * MOTOR_DSHOT_STATE_PER_SYMBOL + 0] |= setMask ; // Always set all ports
buffer[symbol_index * MOTOR_DSHOT_STATE_PER_SYMBOL + 1] = 0; // Reset bits are port dependent
buffer[symbol_index * MOTOR_DSHOT_STATE_PER_SYMBOL + 2] |= resetMask; // Always reset all ports
}
//
// output one more 'bit' that keeps the line level at idle to allow the ESC to sample the last bit
//
// Avoid CRC errors in the case of bi-directional d-shot. CRC errors can occur if the output is
// transitioned to an input before the signal has been sampled by the ESC as the sampled voltage
// may be somewhere between logic-high and logic-low depending on how the motor output line is
// driven or floating. On some MCUs it's observed that the voltage momentarily drops low on transition
// to input.
int hold_bit_index = MOTOR_DSHOT_FRAME_BITS * MOTOR_DSHOT_STATE_PER_SYMBOL;
buffer[hold_bit_index + 0] |= resetMask; // Always reset all ports
buffer[hold_bit_index + 1] = 0; // Never any change
buffer[hold_bit_index + 2] = 0; // Never any change
}
static void bbOutputDataSet(uint32_t *buffer, int pinNumber, uint16_t value, bool inverted)

4
src/main/drivers/dshot_bitbang_impl.h
View file

@ -51,9 +51,11 @@
#define MOTOR_DSHOT_BIT_PER_SYMBOL 1
#define MOTOR_DSHOT_STATE_PER_SYMBOL 3 // Initial high, 0/1, low
#define MOTOR_DSHOT_BIT_HOLD_STATES 3 // 3 extra states at the end of transmission required to allow ESC to sample the last bit correctly.
#define MOTOR_DSHOT_FRAME_BITS 16
#define MOTOR_DSHOT_FRAME_TIME_NS(rate) ((MOTOR_DSHOT_FRAME_BITS / MOTOR_DSHOT_BIT_PER_SYMBOL) * MOTOR_DSHOT_SYMBOL_TIME_NS(rate))
#define MOTOR_DSHOT_TELEMETRY_WINDOW_US (30000 + MOTOR_DSHOT_FRAME_TIME_NS(rate) * (1.1)) / 1000
@ -62,7 +64,7 @@
#define MOTOR_DSHOT_GCR_CHANGE_INTERVAL_NS(rate) (MOTOR_DSHOT_CHANGE_INTERVAL_NS(rate) * 5 / 4)
#define MOTOR_DSHOT_BUF_LENGTH ((MOTOR_DSHOT_FRAME_BITS / MOTOR_DSHOT_BIT_PER_SYMBOL) * MOTOR_DSHOT_STATE_PER_SYMBOL)
#define MOTOR_DSHOT_BUF_LENGTH (((MOTOR_DSHOT_FRAME_BITS / MOTOR_DSHOT_BIT_PER_SYMBOL) * MOTOR_DSHOT_STATE_PER_SYMBOL) + MOTOR_DSHOT_BIT_HOLD_STATES)
#ifdef USE_DSHOT_CACHE_MGMT
// MOTOR_DSHOT_BUF_LENGTH is multiples of uint32_t
// Number of bytes required for buffer