I now have a simple ST7796 sketch running using the JSPI connector pins
instead of D11-13.
@Merlin513 @bmillier @ptillisch
Some reason I don't think it would pass muster with the Zephyr people 
See the code under: #ifdef USE_JSPI_PINS
And the quick and dirty helper function.
#include <elapsedMillis.h>
#include <ST77XX_zephyr.h>
#define USE_JSPI_PINS
#define TFT_DC 4
#define TFT_CS 2
#define TFT_RST 3
// Option 1: use any pins but a little slower
// Note: code will detect if specified pins are the hardware SPI pins
// and will use hardware SPI if appropriate
// For 1.44" and 1.8" TFT with ST7735 use
//ST7735_t3 tft = ST7735_t3(TFT_CS, TFT_DC, TFT_MOSI, TFT_SCK, TFT_RST);
// For 1.54" or other TFT with ST7789, This has worked with some ST7789
// displays without CS pins, for those you can pass in -1 or 0xff for CS
// More notes by the tft.init call
//ST7789_t3 tft = ST7789_t3(TFT_CS, TFT_DC, TFT_MOSI, TFT_SCK, TFT_RST);
// Option 2: must use the hardware SPI pins
// (for UNO thats sclk = 13 and sid = 11) and pin 10 must be
// an output. This is much faster - also required if you want
// to use the microSD card (see the image drawing example)
// For 1.44" and 1.8" TFT with ST7735 use
//ST7735_t3 tft = ST7735_t3(TFT_CS, TFT_DC, TFT_RST);
// For 1.54" TFT with ST7789
//ST7789_t3 tft = ST7789_t3(TFT_CS, TFT_DC, TFT_RST);
// For 3.5" or 4.0" TFT with ST7796
ST7796_zephyr tft = ST7796_zephyr(&SPI, TFT_CS, TFT_DC, TFT_RST);
uint8_t test_screen_rotation = 0;
void set_gpio_pin_mode(GPIO_TypeDef *port, uint8_t pin, uint8_t af) {
// Set the MODER = could be done in fewer steps
uint32_t moder = port->MODER;
uint32_t mask = ~(0x3 << (pin * 2));
moder = (moder & mask) | (0x2 << (pin * 2));
port->MODER = moder;
if (pin < 8) {
port->AFR[0] = port->AFR[0] & ~(0xf << (pin * 4)) | (af << (pin * 4));
} else {
pin -= 8;
port->AFR[1] = port->AFR[1] & ~(0xf << (pin * 4)) | (af << (pin * 4));
}
}
void print_gpio_regs(const char *name, GPIO_TypeDef *port) {
//printk("GPIO%s(%p) %08X %08X %08x\n", name, port, port->MODER, port->AFR[0], port->AFR[1]);
Serial.print("GPIO");
Serial.print(name);
Serial.print(" ");
Serial.print(port->MODER, HEX);
Serial.print(" ");
Serial.print(port->AFR[0], HEX);
Serial.print(" ");
Serial.print(port->AFR[1], HEX);
Serial.print(" ");
Serial.print(port->IDR, HEX);
Serial.print(" ");
Serial.print(port->ODR, HEX);
Serial.print(" ");
uint32_t pupdr = port->PUPDR;
Serial.print(pupdr, HEX);
Serial.print(" : ");
for (uint8_t i = 0; i < 16; i++) {
switch (pupdr & 0xC0000000) {
case 0x00000000ul: Serial.print("-"); break;
case 0x40000000ul: Serial.print("U"); break;
case 0x80000000ul: Serial.print("D"); break;
default: Serial.print("?"); break;
}
pupdr <<= 2;
}
Serial.println();
}
void show_all_gpio_regs() {
print_gpio_regs("A", (GPIO_TypeDef *)GPIOA_BASE);
print_gpio_regs("B", (GPIO_TypeDef *)GPIOB_BASE);
print_gpio_regs("C", (GPIO_TypeDef *)GPIOC_BASE);
print_gpio_regs("D", (GPIO_TypeDef *)GPIOD_BASE);
print_gpio_regs("E", (GPIO_TypeDef *)GPIOE_BASE);
print_gpio_regs("F", (GPIO_TypeDef *)GPIOF_BASE);
print_gpio_regs("G", (GPIO_TypeDef *)GPIOG_BASE);
print_gpio_regs("H", (GPIO_TypeDef *)GPIOH_BASE);
print_gpio_regs("I", (GPIO_TypeDef *)GPIOI_BASE);
}
void setup() {
Serial.begin(115200);
long unsigned debug_start = millis();
while (!Serial && ((millis() - debug_start) <= 5000))
;
Serial.println("Setup");
// Use this initializer if you're using a 1.8" TFT 128x160 displays
//tft.initR(INITR_BLACKTAB);
// Or use this initializer (uncomment) if you're using a 1.44" TFT (128x128)
//tft.initR(INITR_144GREENTAB);
// Or use this initializer (uncomment) if you're using a .96" TFT(160x80)
//tft.initR(INITR_MINI160x80);
// Or use this initializer (uncomment) for Some 1.44" displays use different memory offsets
// Try it if yours is not working properly
// May need to tweek the offsets
//tft.setRowColStart(32,0);
// Or use this initializer (uncomment) if you're using a 1.54" 240x240 TFT
//tft.init(240, 240); // initialize a ST7789 chip, 240x240 pixels
// OR use this initializer (uncomment) if using a 2.0" 320x240 TFT:
//tft.init(240, 320); // Init ST7789 320x240
// OR use this initializer (uncomment) if using a 2.0" 320x240 TFT:
// tft.init(240, 320); // Init ST7789 320x240
// OR use this initializer (uncomment) if using a 240x240 clone
// that does not have a CS pin2.0" 320x240 TFT:
//tft.init(240, 240, SPI_MODE2); // Init ST7789 240x240 no CS
// Or for ST7796 3.5 or 4"
#ifdef USE_JSPI_PINS
// they are pins c2, c3, d1
set_gpio_pin_mode(GPIOC, 2, 5);
set_gpio_pin_mode(GPIOC, 3, 5);
set_gpio_pin_mode(GPIOD, 1, 5);
pinMode(11, INPUT);
pinMode(12, INPUT);
pinMode(13, INPUT);
#endif
tft.init(320, 480);
tft.fillScreen(ST77XX_RED);
show_all_gpio_regs();
}
void loop() {
elapsedMillis em;
tft.fillScreen(ST77XX_BLACK);
tft.fillScreen(ST77XX_NAVY);
tft.fillScreen(ST77XX_DARKGREEN);
tft.fillScreen(ST77XX_DARKCYAN);
tft.fillScreen(ST77XX_MAROON);
tft.fillScreen(ST77XX_PURPLE);
tft.fillScreen(ST77XX_OLIVE);
tft.fillScreen(ST77XX_LIGHTGREY);
tft.fillScreen(ST77XX_DARKGREY);
tft.fillScreen(ST77XX_BLUE);
tft.fillScreen(ST77XX_GREEN);
tft.fillScreen(ST77XX_CYAN);
tft.fillScreen(ST77XX_RED);
tft.fillScreen(ST77XX_MAGENTA);
tft.fillScreen(ST77XX_YELLOW);
tft.fillScreen(ST77XX_WHITE);
tft.fillScreen(ST77XX_ORANGE);
tft.fillScreen(ST77XX_GREENYELLOW);
tft.fillScreen(ST77XX_PINK);
uint32_t dt = em;
#if 0
Serial.print(dt);
delay(250);
em = 0;
tft.fillRectCB(0, 0, tft.width(), tft.height(), ST77XX_BLACK);
tft.fillRectCB(0, 0, tft.width(), tft.height(), ST77XX_NAVY);
tft.fillRectCB(0, 0, tft.width(), tft.height(), ST77XX_DARKGREEN);
tft.fillRectCB(0, 0, tft.width(), tft.height(), ST77XX_DARKCYAN);
tft.fillRectCB(0, 0, tft.width(), tft.height(), ST77XX_MAROON);
tft.fillRectCB(0, 0, tft.width(), tft.height(), ST77XX_PURPLE);
tft.fillRectCB(0, 0, tft.width(), tft.height(), ST77XX_OLIVE);
tft.fillRectCB(0, 0, tft.width(), tft.height(), ST77XX_LIGHTGREY);
tft.fillRectCB(0, 0, tft.width(), tft.height(), ST77XX_DARKGREY);
tft.fillRectCB(0, 0, tft.width(), tft.height(), ST77XX_BLUE);
tft.fillRectCB(0, 0, tft.width(), tft.height(), ST77XX_GREEN);
tft.fillRectCB(0, 0, tft.width(), tft.height(), ST77XX_CYAN);
tft.fillRectCB(0, 0, tft.width(), tft.height(), ST77XX_RED);
tft.fillRectCB(0, 0, tft.width(), tft.height(), ST77XX_MAGENTA);
tft.fillRectCB(0, 0, tft.width(), tft.height(), ST77XX_YELLOW);
tft.fillRectCB(0, 0, tft.width(), tft.height(), ST77XX_WHITE);
tft.fillRectCB(0, 0, tft.width(), tft.height(), ST77XX_ORANGE);
tft.fillRectCB(0, 0, tft.width(), tft.height(), ST77XX_GREENYELLOW);
tft.fillRectCB(0, 0, tft.width(), tft.height(), ST77XX_PINK);
dt = em;
Serial.print(" ");
#endif
Serial.println((uint32_t)em);
}
I know the saying goes: “When in Rome, do as the Romans do”
But sometimes ... 
Hopefully ArduinoTeam will get the SPI fixes into the core before the next release!!!