I haven't had the time to work on the framebuffer driver, since I spent most of the time modelling the shell. Still, I could not continue without taking some nice pictures with the display working. So I coded a little script to use the interface exposed at /dev/spidev and initialise and write to the display. 

Which worked fine. I just had to manually reverse the bytes before writing, since spi0 does not have a LSB option. Apart from that I just did the init sequence from the datasheet and got it working in no time.

Anyways. Like I said, my plan is to code a kernel space driver to be used by linux. The good thing is now at least I have a good setup since everything is wired up and held firmly in place. I can focus more on the software.

The following snippet is part of the display test script. The whole script is in the project files.

GP1294AI_CMD_RESET = 0xAA
GP1294AI_CMD_FRAME_SYNC = 0x08
GP1294AI_CMD_BRIGHTNESS = 0xA0
GP1294AI_CMD_DISPLAY_MODE = 0x80
GP1294AI_CMD_WRITE_GRAM = 0xF0
GP1294AI_CMD_DISPLAY_OFFSET = 0xC0
GP1294AI_CMD_VFD_MODE = 0xCC
GP1294AI_CMD_OSC_SETTING = 0x78
GP1294AI_CMD_EXIT_STANDBY = 0x6D
GP1294AI_CMD_ENTER_STANDBY = 0x61

GP1294AI_MAX_FREQ = 4167000
GP1294AI_DEFAULT_BRIGHTNESS = 0x0028

cmd_reset = [GP1294AI_CMD_RESET]
cmd_init = [GP1294AI_CMD_VFD_MODE, 0x01, 0x01F, 0x00, 0xFF, 0x2F, 0x00, 0x20]
cmd_brightness = [GP1294AI_CMD_BRIGHTNESS, GP1294AI_DEFAULT_BRIGHTNESS & 0xFF, (GP1294AI_DEFAULT_BRIGHTNESS >> 8) & 0xFF]
cmd_offset = [GP1294AI_CMD_DISPLAY_OFFSET, 0x00, 0x00]
cmd_mode = [GP1294AI_CMD_DISPLAY_MODE, 0x00]
cmd_init_osc = [GP1294AI_CMD_OSC_SETTING, 0x08]

# We only have SPI bus 0 available to us on the Pi
bus = 0

#Device is the chip select pin. Set to 0 or 1, depending on the connections
device = 0

# Enable SPI
spi = spidev.SpiDev()

# Open a connection to a specific bus and device (chip select pin)
spi.open(bus, device)

# Set SPI speed and mode
spi.max_speed_hz = 500000
spi.mode = 3

def reverse(array):
    for index, value in enumerate(array):
        array[index] = int('{:08b}'.format(value)[::-1], 2)
    return array

def spi_transfer(array):
    spi.xfer2(reverse(array))

def clear():
    empty_frame = [0] * (256*8)
    payload = [0xF0, 0, 0, 48] + empty_frame
    print(len(payload))
    spi_transfer(payload)

def init():
    spi_transfer(cmd_reset)
    spi_transfer(cmd_init)
    spi_transfer(cmd_brightness)
    clear()
    time.sleep(0.02)
    spi_transfer(cmd_offset)
    spi_transfer(cmd_mode)
    spi_transfer(cmd_init_osc)