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jeplerjepler
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Fast(ish) special purpose bitbang spi over i2c
with the i2c bus operating at 400kHz this achieves a 4.8kHz SPI clock rate which could be worse. It accepts the same style of init sequence as displayio. tested by scoping the pins on the espressif lcd dev kit with a dummy init sequence: ```python dotclockframebuffer.ioexpander_send_init_sequence( bus=bus, i2c_address=expander_addr, gpio_address=1, gpio_data_len=1, gpio_data=0xff, cs_bit=1, mosi_bit=3, clk_bit=2, init_sequence=init_sequence) ```
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‎py/circuitpy_defns.mk‎

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@@ -603,6 +603,7 @@ SRC_SHARED_MODULE_ALL = \
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displayio/TileGrid.c \
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displayio/area.c \
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displayio/__init__.c \
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dotclockframebuffer/__init__.c \
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floppyio/__init__.c \
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fontio/BuiltinFont.c \
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fontio/__init__.c \

‎shared-bindings/dotclockframebuffer/__init__.c‎

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#include "shared-bindings/dotclockframebuffer/DotClockFramebuffer.h"
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//| """Native helpers for driving parallel displays"""
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//|
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//| Length = typing.Literal[1, 2]
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//|
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//| def ioexpander_send_init_sequence(
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//| bus: busio.I2C,
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//| i2c_address: int,
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//| reg_addr: int,
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//| gpio_data_len: Length,
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//| gpio_address: int,
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//| gpio_data: int,
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//| cs_bit: int,
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//| mosi_bit: int,
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//| clk_bit: int,
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//| init_sequence: ReadableBuffer,
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//| ):
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//| """Send a displayio-style initialization sequence over an I2C I/O expander
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//|
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//| This function is highly generic in order to support various I/O expanders.
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//| What's assumed is that all the GPIO can be updated by writing to a single I2C register.
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//| Normal output polarity is assumed (CS and CLK are active low, data is not inverted).
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//| Only 8-bit I2C addresses are supported.
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//| 8- and 16-bit I2C addresses and data registers are supported.
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//| The Data/Command bit is sent as part of the serial data.
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//|
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//| Normally this function is used via a convenience library that is specific to the display & I/O expander in use.
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//|
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//| :param busio.I2C bus: The I2C bus where the I/O expander resides
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//| :param busio.i2c_address: int: The I2C bus address of the I/O expander
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//| :param int gpio_address: The address portion of the I2C transaction (1 byte)
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//| :param int gpio_data_len: The size of the data portion of the I2C transaction, 1 or 2 bytes
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//| :param int gpio_data: The output value for all GPIO bits other than cs, mosi, and clk (needed because GPIO expanders may be unable to read back the current output value)
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//| :param int cs_bit: The bit number (from 0 to 7, or from 0 to 15) of the chip select bit in the GPIO register
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//| :param int mosi_value: The bit number (from 0 to 7, or from 0 to 15) of the data out bit in the GPIO register
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//| :param int clk_value: The bit number (from 0 to 7, or from 0 to 15) of the clock out bit in the GPIO register
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//| """
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//|
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STATIC mp_obj_t ioexpander_send_init_sequence(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
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enum { ARG_bus, ARG_i2c_address, ARG_gpio_address, ARG_gpio_data_len, ARG_gpio_data, ARG_cs_bit, ARG_mosi_bit, ARG_clk_bit, ARG_init_sequence, NUM_ARGS };
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static const mp_arg_t allowed_args[] = {
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{ MP_QSTR_bus, MP_ARG_REQUIRED | MP_ARG_OBJ },
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{ MP_QSTR_i2c_address, MP_ARG_REQUIRED | MP_ARG_INT },
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{ MP_QSTR_gpio_address, MP_ARG_REQUIRED | MP_ARG_INT },
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{ MP_QSTR_gpio_data_len, MP_ARG_REQUIRED | MP_ARG_INT },
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{ MP_QSTR_gpio_data, MP_ARG_REQUIRED | MP_ARG_INT },
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{ MP_QSTR_cs_bit, MP_ARG_REQUIRED | MP_ARG_INT },
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{ MP_QSTR_mosi_bit, MP_ARG_REQUIRED | MP_ARG_INT },
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{ MP_QSTR_clk_bit, MP_ARG_REQUIRED | MP_ARG_INT },
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{ MP_QSTR_init_sequence, MP_ARG_REQUIRED | MP_ARG_OBJ },
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};
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mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
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MP_STATIC_ASSERT(MP_ARRAY_SIZE(allowed_args) == NUM_ARGS);
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mp_arg_parse_all(n_args, pos_args, kw_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
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mp_obj_t bus_obj = mp_arg_validate_type(args[ARG_bus].u_obj, &busio_i2c_type, MP_QSTR_bus);
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mp_int_t i2c_address = args[ARG_i2c_address].u_int;
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mp_int_t gpio_address = args[ARG_gpio_address].u_int;
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mp_int_t gpio_data_len = args[ARG_gpio_data_len].u_int;
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mp_int_t gpio_data = args[ARG_gpio_data].u_int;
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mp_int_t cs_bit = args[ARG_cs_bit].u_int;
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mp_int_t mosi_bit = args[ARG_mosi_bit].u_int;
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mp_int_t clk_bit = args[ARG_clk_bit].u_int;
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mp_buffer_info_t bufinfo;
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mp_get_buffer_raise(args[ARG_init_sequence].u_obj, &bufinfo, MP_BUFFER_READ);
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mp_arg_validate_int_range(i2c_address, 0, 127, MP_QSTR_i2c_address);
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mp_arg_validate_int_range(gpio_data_len, 1, 2, MP_QSTR_gpio_dat_len);
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int max_bit = gpio_data_len * 8 - 1;
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mp_arg_validate_int_range(cs_bit, 0, max_bit, MP_QSTR_cs_bit);
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mp_arg_validate_int_range(mosi_bit, 0, max_bit, MP_QSTR_mosi_bit);
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mp_arg_validate_int_range(clk_bit, 0, max_bit, MP_QSTR_clk_bit);
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mp_arg_validate_int_range(gpio_data, 0, (1 << (max_bit * 8)) - 1, MP_QSTR_gpio_data);
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dotclockframebuffer_ioexpander_spi_bus b = {
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.bus = bus_obj,
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.i2c_device_address = i2c_address,
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.i2c_write_size = 1 + gpio_data_len,
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// ASSERT(LITTLE_ENDIAN, "don't have to differentiate 8- vs 16-bits here")
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.addr_reg_shadow = { .u32 = gpio_address | (gpio_data << 8) },
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.cs_mask = 0x100 << cs_bit,
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.mosi_mask = 0x100 << mosi_bit,
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.clk_mask = 0x100 << clk_bit,
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};
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dotclockframebuffer_ioexpander_send_init_sequence(&b, bufinfo.buf, bufinfo.len);
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return mp_const_none;
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}
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STATIC MP_DEFINE_CONST_FUN_OBJ_KW(ioexpander_send_init_sequence_obj, 0, ioexpander_send_init_sequence);
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STATIC const mp_rom_map_elem_t dotclockframebuffer_module_globals_table[] = {
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{ MP_ROM_QSTR(MP_QSTR___name__), MP_ROM_QSTR(MP_QSTR_dotclockframebuffer) },
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{ MP_ROM_QSTR(MP_QSTR_DotClockFramebuffer), MP_ROM_PTR(&dotclockframebuffer_framebuffer_type) },
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{ MP_ROM_QSTR(MP_QSTR_ioexpander_send_init_sequence), MP_ROM_PTR(&ioexpander_send_init_sequence_obj) },
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};
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STATIC MP_DEFINE_CONST_DICT(dotclockframebuffer_module_globals, dotclockframebuffer_module_globals_table);

‎shared-bindings/dotclockframebuffer/__init__.h‎

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@@ -25,3 +25,32 @@
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*/
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#pragma once
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#include "py/obj.h"
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#include "shared-bindings/busio/I2C.h"
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typedef union {
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struct {
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uint8_t addr, data;
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} a8d8;
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struct {
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uint16_t addr, data; // in little endian
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} a16d16;
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struct {
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uint8_t addr;
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uint16_t data; // in little endian
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} __attribute__((packed)) a8d16;
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uint32_t u32;
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} dotclockframebuffer_ioexpander_addr_reg_t;
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typedef struct {
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busio_i2c_obj_t *bus;
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uint8_t i2c_device_address;
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uint8_t i2c_write_size;
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dotclockframebuffer_ioexpander_addr_reg_t addr_reg_shadow;
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uint32_t cs_mask;
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uint32_t mosi_mask;
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uint32_t clk_mask;
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} dotclockframebuffer_ioexpander_spi_bus;
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void dotclockframebuffer_ioexpander_send_init_sequence(dotclockframebuffer_ioexpander_spi_bus *bus, uint8_t *init_sequence, uint16_t init_sequence_len);

‎shared-module/dotclockframebuffer/__init__.c‎

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#include "shared-bindings/dotclockframebuffer/__init__.h"
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#include <stdint.h>
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#include <stdbool.h>
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#include <stddef.h>
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#define DELAY (0x80)
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static void pin_change(dotclockframebuffer_ioexpander_spi_bus *bus, uint32_t set_bits, uint32_t clear_bits) {
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uint32_t data = (bus->addr_reg_shadow.u32 & ~clear_bits) | set_bits;
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// no way to signal failure to caller!
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(void)common_hal_busio_i2c_write(bus->bus, bus->i2c_device_address, (uint8_t *)&data, bus->i2c_write_size);
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bus->addr_reg_shadow.u32 = data;
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}
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static void ioexpander_bus_send(dotclockframebuffer_ioexpander_spi_bus *bus,
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bool is_command,
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const uint8_t *data, uint32_t data_length) {
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int dc_mask = is_command ? 0 : 0x100;
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for (uint32_t i = 0; i < data_length; i++) {
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int bits = data[i] | dc_mask;
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for (uint32_t j = 0; j < 9; j++) {
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// CPOL=CPHA=0: output fresh data on falling edge of clk or cs
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if (bits & 0x100) {
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pin_change(bus, /* set */ bus->mosi_mask, /* clear */ bus->clk_mask | bus->cs_mask);
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} else {
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pin_change(bus, /* set */ 0, /* clear */ bus->mosi_mask | bus->clk_mask | bus->cs_mask);
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}
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// Display latches bit on rising edge of CLK
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pin_change(bus, /* set */ bus->clk_mask, /* clear */ 0);
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// next bit
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bits <<= 1;
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}
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}
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}
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// Send a circuitpython-style display initialization sequence over an i2c-attached bus expander
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// This always assumes
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// * 9-bit SPI (no DC pin)
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// * CPOL=CPHA=0
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// * CS deasserted after each init sequence step, but not otherwise just like
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// displayio fourwire bus without data_as_commands
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void dotclockframebuffer_ioexpander_send_init_sequence(dotclockframebuffer_ioexpander_spi_bus *bus, uint8_t *init_sequence, uint16_t init_sequence_len) {
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while (!common_hal_busio_i2c_try_lock(bus->bus)) {
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RUN_BACKGROUND_TASKS;
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}
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for (uint32_t i = 0; i < init_sequence_len; /* NO INCREMENT */) {
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uint8_t *cmd = init_sequence + i;
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uint8_t data_size = *(cmd + 1);
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bool delay = (data_size & DELAY) != 0;
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data_size &= ~DELAY;
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uint8_t *data = cmd + 2;
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ioexpander_bus_send(bus, true, cmd, 1);
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ioexpander_bus_send(bus, false, data, data_size);
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// deassert CS
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pin_change(bus, /* set */ bus->cs_mask, /* clear */ 0);
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uint16_t delay_length_ms = 10;
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if (delay) {
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data_size++;
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delay_length_ms = *(cmd + 1 + data_size);
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if (delay_length_ms == 255) {
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delay_length_ms = 500;
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}
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}
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mp_hal_delay_ms(delay_length_ms);
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i += 2 + data_size;
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}
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common_hal_busio_i2c_unlock(bus->bus);
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}

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