Bitbang

Github Repo	C Header	C source	JS source
cesanta/mongoose-os	mgos_bitbang.h	mgos_bitbang.c	api_bitbang.js

Bit banging is a technique to implement hardware protocols fully in software, by managing microcontroller pin states - including timing, voltage levels, etc. See wikipedia article for a detailed information.

Usage example:

#include "mgos_bitbang.h"
#include "mgos_gpio.h"
#include "mgos_system.h"

void mgos_neopixel_show(struct mgos_neopixel *np) {
  mgos_gpio_write(np->pin, 0);
  mgos_usleep(60);
  mgos_bitbang_write_bits(np->pin, MGOS_DELAY_100NSEC, 3, 8, 8, 6, np->data,
                          np->num_pixels * NUM_CHANNELS);
  mgos_gpio_write(np->pin, 0);
  mgos_usleep(60);
  mgos_gpio_write(np->pin, 1);
}

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mgos_bitbang_write_bits

void mgos_bitbang_write_bits(int gpio, enum mgos_delay_unit delay_unit, int t0h,
                             int t0l, int t1h, int t1l, const uint8_t *data,
                             size_t len);

Bit bang GPIO pin gpio. len bytes from data are sent to the specified pin bit by bit. Sending each bit consists of a "high" and "low" phases, length of which is determined by the specified timing parameters.

 +-----+
 |     |
-+     +-------

 tXh   tXl

t0h and t0l specify timings if the bit being transmitted is 0, t1h and t1l specify the same for the case where the bit is 1. If any of these is < 0, the corresponding phase is skipped.

mgos_bitbang_write_bits_js

void mgos_bitbang_write_bits_js(int gpio, enum mgos_delay_unit delay_unit,
                                uint32_t t, const uint8_t *data, size_t len);

This function is a wrapper for mgos_bitbang_write_bits(). It has smaller number of arguments (less than 6) and therefore could be FFI-ed to JavaScript. Essentially, it just packs all time patterns into a single value t.

JS API

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BitBang.write

BitBang.write(pin, delay_unit, t0h, t0l, t1h, t1l, ptr, len)

Write bits to a given pin. delay_unit is one of the: BitBang.DELAY_MSEC, BitBang.DELAY_USEC, BitBang.DELAY_100NSEC. ptr, len is a bit pattern to write. t0h, t0l is the time pattern for zero bit, t1h, t1l is the time pattern for 1. The time pattern specifies the number of time units to hold the pin high, and the number of units to hold the pin low. Return value: none.

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