/* This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */
/** library to drive vacuum fluorescent display using supertex HV518 shift register VFD drivers (code)
 *  @details the current configuration is for a VFD extracted from a Samsung SER-6500 cash register
 *  @file vfd_hv518.c
 *  @author King Kévin <kingkevin@cuvoodoo.info>
 *  @date 2016
 *  @note peripherals used: SPI @ref vfd_hv518_spi , GPIO @ref vfd_hv518_gpio , timer @ref vfd_hv518_timer
 */
/* standard libraries */
#include <stdint.h> // standard integer types
#include <stdlib.h> // general utilities

/* STM32 (including CM3) libraries */
#include <libopencm3/stm32/rcc.h> // real-time control clock library
#include <libopencm3/stm32/gpio.h> // general purpose input output library
#include <libopencm3/stm32/spi.h> // SPI library
#include <libopencm3/stm32/timer.h> // timer library
#include <libopencm3/cm3/nvic.h> // interrupt handler

#include "global.h" // global definitions
#include "vfd_hv518.h" // VFD library API

/** @defgroup vfd_hv518_gpio GPIO to control supertex HV518 VFD drivers
 *  @{
 */
#define VFD_PORT GPIOA /**< GPIO port */
#define VFD_PORT_RCC RCC_GPIOA /**< GPIO port peripheral clock */
#define VFD_STR GPIO6 /**< strobe pin to enable high voltage output, high voltage is output on low */
#define VFD_NLE GPIO4 /**< latch enable pin, stores the shifted data on low, output the parallel data on high */
/** @} */

/** @defgroup vfd_hv518_spi SPI to send data to supertex HV518 VFD drivers
 *  @{
 */
#define VFD_SPI_RCC RCC_SPI1 /**< SPI peripheral */
#define VFD_SPI_PORT GPIOA /**< GPIO port */
#define VFD_SPI_PORT_RCC RCC_GPIOA /**< GPIO port peripheral clock */
#define VFD_SPI_IRQ NVIC_SPI1_IRQ /**< SPI peripheral interrupt signal */
#define VFD_SPI_ISR spi1_isr /**< SPI interrupt service routine */
#define VFD_CLK GPIO_SPI1_SCK /**< clock signal */
#define VFD_DIN GPIO_SPI1_MOSI /**< data input, where the data is shifted to */
/** @} */

/** @defgroup vfd_hv518_timer timer for automatic display blocks refresh
 *  @{
 */
#define VFD_TIMER_RCC RCC_TIM2 /**< timer peripheral clock */
#define VFD_TIMER_IRQ NVIC_TIM2_IRQ /**< timer interrupt signal */
#define VFD_TIMER_ISR tim2_isr /**< timer interrupt service routine */
/** @} */

/** ASCII characters encoded for the 7 segments digit block
 *  @note starts with space
 */
static const uint8_t ascii_7segments[] = {
	0b00000000, // space
	0b00110000, // ! (I)
	0b00100010, // "
	0b01011100, // # (o)
	0b01101101, // $ (s)
	0b01010010, // % (/)
	0b01111101, // & (6)
	0b00100000, // '
	0b00111001, // ( ([)
	0b00001111, // )
	0b01110000, // *
	0b01000110, // +
	0b00010000, // ,
	0b01000000, // -
	0b00010000, // . (,)
	0b01010010, // /
	0b00111111, // 0
	0b00000110, // 1
	0b01011011, // 2
	0b01001111, // 3
	0b01100110, // 4
	0b01101101, // 5
	0b01111101, // 6
	0b00000111, // 7
	0b01111111, // 8
	0b01101111, // 9
	0b01001000, // : (=)
	0b01001000, // ; (=)
	0b01011000, // <
	0b01001000, // =
	0b01001100, // >
	0b01010011, // ?
	0b01111011, // @
	0b01110111, // A
	0b01111111, // B
	0b00111001, // C
	0b01011110, // D
	0b01111001, // E
	0b01110001, // F
	0b00111101, // G
	0b01110110, // H
	0b00110000, // I
	0b00011110, // J
	0b01110110, // K
	0b00111000, // L
	0b00110111, // M
	0b00110111, // N
	0b00111111, // O
	0b01110011, // P
	0b01101011, // Q
	0b00110011, // R
	0b01101101, // S
	0b01111000, // T
	0b00111110, // U
	0b00111110, // V (U)
	0b00111110, // W (U)
	0b01110110, // X (H)
	0b01101110, // Y
	0b01011011, // Z
	0b00111001, // [
	0b01100100, // '\'
	0b00001111, // /
	0b00100011, // ^
	0b00001000, // _
	0b00000010, // `
	0b01011111, // a
	0b01111100, // b
	0b01011000, // c
	0b01011110, // d
	0b01111011, // e
	0b01110001, // f
	0b01101111, // g
	0b01110100, // h
	0b00010000, // i
	0b00001100, // j
	0b01110110, // k
	0b00110000, // l
	0b01010100, // m
	0b01010100, // n
	0b01011100, // o
	0b01110011, // p
	0b01100111, // q
	0b01010000, // r
	0b01101101, // s
	0b01111000, // t
	0b00011100, // u
	0b00011100, // v (u)
	0b00011100, // w (u)
	0b01110110, // x
	0b01101110, // y
	0b01011011, // z
	0b00111001, // { ([)
	0b00110000, // |
	0b00001111, // } ([)
	0b01000000, // ~
};

/** font for the 5x7 dot matrix block
 * @details first value is left-most line, LSB is top dot, MSB is not used
 * @note from http://sunge.awardspace.com/glcd-sd/node4.html
 */
static const uint8_t font5x7[][5] = {
	{0x00, 0x00, 0x00, 0x00, 0x00}, // (space)
	{0x00, 0x00, 0x5F, 0x00, 0x00}, // !
	{0x00, 0x07, 0x00, 0x07, 0x00}, // "
	{0x14, 0x7F, 0x14, 0x7F, 0x14}, // #
	{0x24, 0x2A, 0x7F, 0x2A, 0x12}, // $
	{0x23, 0x13, 0x08, 0x64, 0x62}, // %
	{0x36, 0x49, 0x55, 0x22, 0x50}, // &
	{0x00, 0x05, 0x03, 0x00, 0x00}, // '
	{0x00, 0x1C, 0x22, 0x41, 0x00}, // (
	{0x00, 0x41, 0x22, 0x1C, 0x00}, // )
	{0x08, 0x2A, 0x1C, 0x2A, 0x08}, // *
	{0x08, 0x08, 0x3E, 0x08, 0x08}, // +
	{0x00, 0x50, 0x30, 0x00, 0x00}, // ,
	{0x08, 0x08, 0x08, 0x08, 0x08}, // -
	{0x00, 0x60, 0x60, 0x00, 0x00}, // .
	{0x20, 0x10, 0x08, 0x04, 0x02}, // /
	{0x3E, 0x51, 0x49, 0x45, 0x3E}, // 0
	{0x00, 0x42, 0x7F, 0x40, 0x00}, // 1
	{0x42, 0x61, 0x51, 0x49, 0x46}, // 2
	{0x21, 0x41, 0x45, 0x4B, 0x31}, // 3
	{0x18, 0x14, 0x12, 0x7F, 0x10}, // 4
	{0x27, 0x45, 0x45, 0x45, 0x39}, // 5
	{0x3C, 0x4A, 0x49, 0x49, 0x30}, // 6
	{0x01, 0x71, 0x09, 0x05, 0x03}, // 7
	{0x36, 0x49, 0x49, 0x49, 0x36}, // 8
	{0x06, 0x49, 0x49, 0x29, 0x1E}, // 9
	{0x00, 0x36, 0x36, 0x00, 0x00}, // :
	{0x00, 0x56, 0x36, 0x00, 0x00}, // ;
	{0x00, 0x08, 0x14, 0x22, 0x41}, // <
	{0x14, 0x14, 0x14, 0x14, 0x14}, // =
	{0x41, 0x22, 0x14, 0x08, 0x00}, // >
	{0x02, 0x01, 0x51, 0x09, 0x06}, // ?
	{0x32, 0x49, 0x79, 0x41, 0x3E}, // @
	{0x7E, 0x11, 0x11, 0x11, 0x7E}, // A
	{0x7F, 0x49, 0x49, 0x49, 0x36}, // B
	{0x3E, 0x41, 0x41, 0x41, 0x22}, // C
	{0x7F, 0x41, 0x41, 0x22, 0x1C}, // D
	{0x7F, 0x49, 0x49, 0x49, 0x41}, // E
	{0x7F, 0x09, 0x09, 0x01, 0x01}, // F
	{0x3E, 0x41, 0x41, 0x51, 0x32}, // G
	{0x7F, 0x08, 0x08, 0x08, 0x7F}, // H
	{0x00, 0x41, 0x7F, 0x41, 0x00}, // I
	{0x20, 0x40, 0x41, 0x3F, 0x01}, // J
	{0x7F, 0x08, 0x14, 0x22, 0x41}, // K
	{0x7F, 0x40, 0x40, 0x40, 0x40}, // L
	{0x7F, 0x02, 0x04, 0x02, 0x7F}, // M
	{0x7F, 0x04, 0x08, 0x10, 0x7F}, // N
	{0x3E, 0x41, 0x41, 0x41, 0x3E}, // O
	{0x7F, 0x09, 0x09, 0x09, 0x06}, // P
	{0x3E, 0x41, 0x51, 0x21, 0x5E}, // Q
	{0x7F, 0x09, 0x19, 0x29, 0x46}, // R
	{0x46, 0x49, 0x49, 0x49, 0x31}, // S
	{0x01, 0x01, 0x7F, 0x01, 0x01}, // T
	{0x3F, 0x40, 0x40, 0x40, 0x3F}, // U
	{0x1F, 0x20, 0x40, 0x20, 0x1F}, // V
	{0x7F, 0x20, 0x18, 0x20, 0x7F}, // W
	{0x63, 0x14, 0x08, 0x14, 0x63}, // X
	{0x03, 0x04, 0x78, 0x04, 0x03}, // Y
	{0x61, 0x51, 0x49, 0x45, 0x43}, // Z
	{0x00, 0x00, 0x7F, 0x41, 0x41}, // [
	{0x02, 0x04, 0x08, 0x10, 0x20}, // '\'
	{0x41, 0x41, 0x7F, 0x00, 0x00}, // ]
	{0x04, 0x02, 0x01, 0x02, 0x04}, // ^
	{0x40, 0x40, 0x40, 0x40, 0x40}, // _
	{0x00, 0x01, 0x02, 0x04, 0x00}, // `
	{0x20, 0x54, 0x54, 0x54, 0x78}, // a
	{0x7F, 0x48, 0x44, 0x44, 0x38}, // b
	{0x38, 0x44, 0x44, 0x44, 0x20}, // c
	{0x38, 0x44, 0x44, 0x48, 0x7F}, // d
	{0x38, 0x54, 0x54, 0x54, 0x18}, // e
	{0x08, 0x7E, 0x09, 0x01, 0x02}, // f
	{0x08, 0x14, 0x54, 0x54, 0x3C}, // g
	{0x7F, 0x08, 0x04, 0x04, 0x78}, // h
	{0x00, 0x44, 0x7D, 0x40, 0x00}, // i
	{0x20, 0x40, 0x44, 0x3D, 0x00}, // j
	{0x00, 0x7F, 0x10, 0x28, 0x44}, // k
	{0x00, 0x41, 0x7F, 0x40, 0x00}, // l
	{0x7C, 0x04, 0x18, 0x04, 0x78}, // m
	{0x7C, 0x08, 0x04, 0x04, 0x78}, // n
	{0x38, 0x44, 0x44, 0x44, 0x38}, // o
	{0x7C, 0x14, 0x14, 0x14, 0x08}, // p
	{0x08, 0x14, 0x14, 0x18, 0x7C}, // q
	{0x7C, 0x08, 0x04, 0x04, 0x08}, // r
	{0x48, 0x54, 0x54, 0x54, 0x20}, // s
	{0x04, 0x3F, 0x44, 0x40, 0x20}, // t
	{0x3C, 0x40, 0x40, 0x20, 0x7C}, // u
	{0x1C, 0x20, 0x40, 0x20, 0x1C}, // v
	{0x3C, 0x40, 0x30, 0x40, 0x3C}, // w
	{0x44, 0x28, 0x10, 0x28, 0x44}, // x
	{0x0C, 0x50, 0x50, 0x50, 0x3C}, // y
	{0x44, 0x64, 0x54, 0x4C, 0x44}, // z
	{0x00, 0x08, 0x36, 0x41, 0x00}, // {
	{0x00, 0x00, 0x7F, 0x00, 0x00}, // |
	{0x00, 0x41, 0x36, 0x08, 0x00}, // }
	{0b00001000, 0b00000100, 0b00001100, 0b00001000, 0b00000100} // ~
};

/** pictures for the 5x7 dot matrix block
 *  @details first value is left-most line, LSB is top dot, MSB is not used
 */
static const uint8_t pict5x7[][5] = {
	{0x08, 0x08, 0x2A, 0x1C, 0x08}, // ->
	{0x08, 0x1C, 0x2A, 0x08, 0x08}, // <-
	{0b01110000, 0b01110000, 0b01111010, 0b01111100, 0b01011000}, // bunny side 1
	{0b00100000, 0b01110000, 0b01110010, 0b01111100, 0b01011000}, // bunny side 2
	{0b00111110, 0b01001001, 0b01010110, 0b01001001, 0b00111110}, // bunny face 1
	{0b00111110, 0b01010001, 0b01100110, 0b01010001, 0b00111110}, // bunny face 2
	{0b00111000, 0b01010111, 0b01100100, 0b01010111, 0b00111000}, // bunny face 3
	{0b00111000, 0b01001111, 0b01010100, 0b01001111, 0b00111000}, // bunny face 4
	{0b00111000, 0b01011110, 0b01101000, 0b01011110, 0b00111000}, // bunny face 5
	{0b01000001, 0b00110110, 0b00001000, 0b00110110, 0b01000001}, // cross 1
	{~0b01000001, ~0b00110110, ~0b00001000, ~0b00110110, ~0b01000001}, // cross 1 negated
	{0b00100010, 0b00010100, 0b00001000, 0b00010100, 0b00100010}, // cross 2
	{~0b00100010, ~0b00010100, ~0b00001000, ~0b00010100, ~0b00100010}, // cross 2 negated
	{0x00, 0x00, 0x00, 0x00, 0x00} // nothing
};

/** the 32 bits values to be shifted out to the VFD driver
 *  @note split into 16 bit for SPI transfer
 *  @note since the bits for digits and matrix are independent, they can be combined
 *  @note we have more matrix (12) than digits (10)
 */
static uint16_t driver_data[VFD_MATRIX][VFD_DRIVERS*2] = {0};
/** which driver data is being transmitted */
static volatile uint8_t spi_i = 0;
/** which grid/part to activate 
 *  @note digits and matrix can be combined
 */
static volatile uint8_t vfd_grid = 0;
/** the bits used for selecting then digit and 7 segment anodes
 *  @note for the second driver
 */
static const uint32_t digit_mask = 0x00fffff0;

void vfd_digit(uint8_t nb, char c)
{
	if (!(nb<VFD_DIGITS)) { // check the digit exists
		return;
	}

	uint32_t digit_data = 0; // the data to be shifted out for the driver (for the second driver)
	
	digit_data = 1<<(4+(9-nb)); // select digit
	/* encode segment
	 * here the bit order (classic 7 segment + underline and dot)
	 *   3_
	 * 8|9_|4
	 * 7|6_|5.1
	 *   0_2,
	 * */
	if (false) { // add the underline (not encoded)
		digit_data |= (1<<(14));
	}
	if (c&0x80) { // add the dot (encoded in the 8th bit)
		digit_data |= (1<<(15));
	}
	if (false) { // add the comma (not encoded)
		digit_data |= (1<<(16));
	}
	
	c &= 0x7f; // only take the ASCII part
	if (c>=' ') { // only take printable characters
		uint8_t i = c-' '; // get index for character
		if (i<LENGTH(ascii_7segments)) {
			digit_data |= (ascii_7segments[i]<<(17)); // add encoded segments to memory
		}
	}

	digit_data &= digit_mask; // be sure only the bits for the digit are used
	digit_data |= (driver_data[nb][2]+(driver_data[nb][3]<<16))&~digit_mask; // get the existing data and add the bits for the digit
	driver_data[nb][2] = digit_data; // write back data (least significant half)
	driver_data[nb][3] = (digit_data>>16); // write back data (most significant half)
}

void vfd_matrix(uint8_t nb, char c)
{
	// check the matrix exists
	if (!(nb<VFD_MATRIX)) { 
		return;
	} 
	
	uint32_t matrix_data[VFD_DRIVERS] = {0}; // the data to be shifted out for the driver
	
	// select matrix
	if (nb<4) {
		matrix_data[1] = 1<<(3-nb); 
	} else {
		matrix_data[0] = 1<<(35-nb);
	}
	
	if ((c<0x80) && (c>=' ')) { // only take printable characters
		uint8_t i = c-' '; // get index for character
		if (i<LENGTH(font5x7)) {
			matrix_data[1] |= font5x7[i][0]<<24;
			matrix_data[2] |= font5x7[i][1]<<0;
			matrix_data[2] |= font5x7[i][2]<<8;
			matrix_data[2] |= font5x7[i][3]<<16;
			matrix_data[2] |= font5x7[i][4]<<24;
		}
	} else if (c>0x7f) { // the non ASCII character are used for pictures
		uint8_t i = c-0x80; // get index for character
		if (i<LENGTH(pict5x7)) {
			matrix_data[1] |= pict5x7[i][0]<<24;
			matrix_data[2] |= pict5x7[i][1]<<0;
			matrix_data[2] |= pict5x7[i][2]<<8;
			matrix_data[2] |= pict5x7[i][3]<<16;
			matrix_data[2] |= pict5x7[i][4]<<24;
		}
	}

	matrix_data[1] &= ~digit_mask; // be sure only the bits for the matrix are used
	matrix_data[1] |= (driver_data[nb][2]+(driver_data[nb][3]<<16))&digit_mask; // get the existing data for the digit
	// prepare the data for SPI to shift it out
	for (uint8_t i=0; i<LENGTH(matrix_data); i++) {
		driver_data[nb][i*2] = matrix_data[i];
		driver_data[nb][i*2+1] = matrix_data[i]>>16;
	}
}

void vfd_clear(void)
{
	for (uint8_t i=0; i<LENGTH(driver_data); i++) {
		for (uint8_t j=0; j<LENGTH(driver_data[0]); j++) {
			driver_data[i][j] = 0;
		}
	}
}

void vfd_test(void)
{
	for (uint8_t i=0; i<LENGTH(driver_data); i++) {
		for (uint8_t j=0; j<LENGTH(driver_data[0]); j++) {
			driver_data[i][j] = ~0;
		}
	}
}

void vfd_on(void)
{
	gpio_clear(VFD_PORT, VFD_STR); // enable HV output
	timer_enable_counter(VFD_TIMER); // start timer to periodically output that to the parts
}

void vfd_off(void)
{
	gpio_set(VFD_PORT, VFD_STR); // disable HV output
	timer_disable_counter(VFD_TIMER); // stop timer to periodically output that to the parts
}

void vfd_setup(void)
{
	/* setup GPIO to control the VFD */
	rcc_periph_clock_enable(VFD_PORT_RCC); // enable clock for VFD GPIO
	gpio_set_mode(VFD_PORT, GPIO_MODE_OUTPUT_50_MHZ, GPIO_CNF_OUTPUT_PUSHPULL, VFD_STR); // set VFD pin to output push-pull
	gpio_set_mode(VFD_PORT, GPIO_MODE_OUTPUT_50_MHZ, GPIO_CNF_OUTPUT_PUSHPULL, VFD_NLE); // set VFD pin to output push-pull
	
	gpio_set(VFD_PORT, VFD_STR); // disable HV output
	gpio_clear(VFD_PORT, VFD_NLE); // do not output latched data
	
	/* setup SPI to transmit data */
	rcc_periph_clock_enable(VFD_SPI_RCC); // enable SPI clock
    rcc_periph_clock_enable(VFD_SPI_PORT_RCC); // enable clock for VFD SPI GPIO
	gpio_set_mode(VFD_SPI_PORT, GPIO_MODE_OUTPUT_50_MHZ, GPIO_CNF_OUTPUT_ALTFN_PUSHPULL, VFD_CLK); // set VFD pin to alternative function push-pull
	gpio_set_mode(VFD_SPI_PORT, GPIO_MODE_OUTPUT_50_MHZ, GPIO_CNF_OUTPUT_ALTFN_PUSHPULL, VFD_DIN); // set VFD pin to alternative function push-pull

	spi_reset(VFD_SPI); // clear SPI values
	/* set SPI:
	 * - use VFD_SPI port
	 * - divide clock by 8 for generating the baudrate (F_PCLK1 is 36MHz, max HV518 is 6MHz)
	 * - clock idle high polarity
	 * - data is valid on rising edge (second clock phase)
	 * - send 16 bits at a time
	 * - send least significant bit first (that's how I coded the data)
	 */
	spi_init_master(VFD_SPI, SPI_CR1_BAUDRATE_FPCLK_DIV_8, SPI_CR1_CPOL_CLK_TO_1_WHEN_IDLE, SPI_CR1_CPHA_CLK_TRANSITION_2, SPI_CR1_DFF_16BIT, SPI_CR1_LSBFIRST);
	//spi_set_bidirectional_transmit_only_mode(VFD_SPI); // only use MOSI to transmit
	spi_set_unidirectional_mode(VFD_SPI); // MISO is unused
	/* set NSS high to enable transmission
	 * the NSS in STM32 can not be used as hardware slave select
	 * RM0008 reference manual 25.3.1 is misleading
	 * when hardware NSS is used and output is enabled NSS never goes up after transmission, even if SPI is disabled
	 * when software NSS is used, NSS can not be set high again, even when writing to the register
	 * the slave select must be done manually using GPIO */
	spi_enable_software_slave_management(VFD_SPI); 
	spi_set_nss_high(VFD_SPI); // set NSS high
	
    nvic_enable_irq(VFD_SPI_IRQ); // enable SPI interrupt
	spi_enable(VFD_SPI); // enable SPI (the tx empty interrupt will trigger)
	
	/* setup timer to refresh display */
	rcc_periph_clock_enable(VFD_TIMER_RCC); // enable clock for timer block
	timer_reset(VFD_TIMER); // reset timer state
	timer_set_mode(VFD_TIMER, TIM_CR1_CKD_CK_INT, TIM_CR1_CMS_EDGE, TIM_CR1_DIR_UP); // set timer mode, use undivided timer clock,edge alignment (simple count), and count up
	timer_set_prescaler(VFD_TIMER, (SYSTEM_CLOCK_FREQ/(1<<16))-1); // set the prescaler so this 16 bits timer overflows at 1Hz
	timer_set_period(VFD_TIMER, 0xffff/LENGTH(driver_data)/100); // set the refresh frequency
	timer_enable_irq(VFD_TIMER, TIM_DIER_UIE); // enable interrupt for timer
	nvic_enable_irq(VFD_TIMER_IRQ); // allow interrupt for timer
	
	vfd_clear(); // initialize values
}

/** SPI interrupt service routine called when data has been transmitted */
void VFD_SPI_ISR(void)
{
	if (SPI_SR(VFD_SPI) & SPI_SR_TXE) { // transmission buffer empty
		if (spi_i<LENGTH(driver_data[0])) { // check if data is available
			gpio_clear(VFD_PORT, VFD_NLE); // slave select to latch data
			spi_send(VFD_SPI, driver_data[vfd_grid][spi_i++]); // send next data
		} else { // all data transmitted
			spi_disable_tx_buffer_empty_interrupt(VFD_SPI); // no need to wait for new data
			while (SPI_SR(VFD_SPI) & SPI_SR_BSY); // wait for data to be shifted out
			spi_disable_tx_buffer_empty_interrupt(VFD_SPI); // no need to wait for new data
			gpio_set(VFD_PORT, VFD_NLE); // output latched data
		}
	}
}

/** timer interrupt service routine called time passed */
void VFD_TIMER_ISR(void)
{
	if (timer_get_flag(VFD_TIMER, TIM_SR_UIF)) { // overflow even happened
		timer_clear_flag(VFD_TIMER, TIM_SR_UIF); // clear flag
    	spi_i = 0; // set the register to shift out
		spi_enable_tx_buffer_empty_interrupt(VFD_SPI); // enable TX empty interrupt
		vfd_grid = (vfd_grid+1)%LENGTH(driver_data); // got to next segment
	}
}