diff options
| -rw-r--r-- | src/neopixel.c | 58 |
1 files changed, 38 insertions, 20 deletions
diff --git a/src/neopixel.c b/src/neopixel.c index 6a5460c3..b799b516 100644 --- a/src/neopixel.c +++ b/src/neopixel.c @@ -28,12 +28,22 @@ command_config_neopixel(uint32_t *args) DECL_COMMAND(command_config_neopixel, "config_neopixel oid=%c pin=%u"); #endif -uint32_t +static uint32_t timer_from_ns(uint32_t ns) { return timer_from_us(ns * 1000) / 1000000; } +// The WS2812 uses a bit-banging protocol where each bit is +// transmitted as a gpio high pulse of variable length. The various +// specs are unclear, but it is believed the timing requirements are: +// - A zero bit must have a high pulse less than 500ns. +// - A one bit must have a high pulse longer than 650ns. +// - The total bit time (gpio high to following gpio high) must not +// exceed ~5000ns. The average bit time must be at least 1250ns. +// - The specs generally indicate a minimum high pulse and low pulse +// of 200ns, but the actual requirement might be smaller. + static int send_data(struct neopixel_s *n, uint8_t *data, uint_fast8_t data_len) { @@ -51,47 +61,55 @@ send_data(struct neopixel_s *n, uint8_t *data, uint_fast8_t data_len) uint_fast8_t bits = 8; while (bits--) { // Calculate pulse duration - uint32_t on, off; - if (byte & 0x80) { - on = timer_from_ns(700 - 150); - off = timer_from_ns(600 - 150); - } else { - on = timer_from_ns(350 - 150); - off = timer_from_ns(800 - 150); - } - byte <<= 1; + uint32_t on; + if (byte & 0x80) + on = timer_from_ns(650); + else + on = timer_from_ns(200); // Set output high do { irq_poll(); cur = timer_read_time(); } while (timer_is_before(cur, min_wait_time)); + uint32_t off_end_time = cur; gpio_out_write(pin, 1); uint32_t on_start_time = timer_read_time(); - if (timer_is_before(max_wait_time, on_start_time)) - goto fail; min_wait_time = on_start_time + on; - max_wait_time = cur + on + timer_from_ns(300); // Set output low do { irq_poll(); cur = timer_read_time(); } while (timer_is_before(cur, min_wait_time)); + uint32_t on_end_time = cur; gpio_out_write(pin, 0); - uint32_t off_start_time = timer_read_time(); - if (timer_is_before(max_wait_time, off_start_time)) + uint32_t off_start_time = cur = timer_read_time(); + min_wait_time = on_start_time + timer_from_ns(1250); + + // Check for faults + if (byte & 0x80) { + // Make sure off for at least 200ns + uint32_t min_off = off_start_time + timer_from_ns(200); + if (timer_is_before(min_wait_time, min_off)) + min_wait_time = min_off; + } else { + // Make sure short on duration was no more than 500ns + uint32_t max_off = off_end_time + timer_from_ns(500); + if (timer_is_before(max_off, off_start_time)) + goto fail; + } + byte <<= 1; + if (timer_is_before(max_wait_time, on_start_time)) goto fail; - min_wait_time = off_start_time + off; - max_wait_time = cur + off + timer_from_ns(300); + max_wait_time = on_end_time + timer_from_us(4); } } - n->last_req_time = timer_read_time(); + n->last_req_time = cur; return 0; fail: // A hardware irq messed up the transmission - report a failure - gpio_out_write(pin, 0); - n->last_req_time = timer_read_time(); + n->last_req_time = cur; return -1; } |