Normally we talk to #ST7789 SPI Display in 4-Wire (8-bit) Mode ... But today we do 3-Wire (9-bit) Mode ... With a sneaky packing hack

https://www.rhydolabz.com/documents/33/ST7789.pdf

How we pack 9-bit #ST7789 data ... Into 8-bit SPI

https://github.com/lupyuen/bl_iot_sdk/blob/3wire/customer_app/pinedio_st7789/pinedio_st7789/display.c#L299-L406

Now we test the code that packs #ST7789 9-bit data into 8-bit SPI

https://github.com/lupyuen/bl_iot_sdk/blob/3wire/customer_app/pinedio_st7789/pinedio_st7789/display.c#L338-L404

Packed #ST7789 9-bit data looks correct ... But nothing appears on #PineDio Stack Display 🤔

https://github.com/lupyuen/bl_iot_sdk/blob/3wire/customer_app/pinedio_st7789/pinedio_st7789/demo.c#L227-L2661

We're sending SPI data to #ST7789 in multiples of 9 Bytes ... Due to the 9-bit packing

https://github.com/lupyuen/bl_iot_sdk/blob/3wire/customer_app/pinedio_st7789/pinedio_st7789/demo.c#L227-L2661

Since our #ST7789 Driver Code is in C, let's test it locally on Linux!

https://github.com/lupyuen/bl_iot_sdk/blob/3wire/customer_app/pinedio_st7789/pinedio_st7789/display.c

#PineDio Stack SPI Port is exposed on the GPIO Connector ... Shall we connect a Logic Analyser to troubleshoot #ST7789 Display? 🤔

https://github.com/lupyuen/bl_iot_sdk/blob/3wire/customer_app/pinedio_st7789/pinedio_st7789/demo.c#L227-L2661

Verifying the packed #ST7789 9-bit data with a spreadsheet ... Our packing is indeed correct 🤔

https://docs.google.com/spreadsheets/d/1Qy0MjU79s__wzTAFwpTYUUIzLWcrFnKCrvvo_rHamiE/edit?usp=sharing

Let's connect a Logic Analyser to #PineDio Stack #BL604 ... And troubleshoot the SPI connection to ST7789 Display

#PineDio Stack SPI Port is exposed on the GPIO Connector ... So we connect our Logic Analyser there

https://github.com/lupyuen/bl_iot_sdk/blob/3wire/customer_app/pinedio_st7789/pinedio_st7789/display.h#L48-L58

ST7789's CS Pin (GPIO 20) is not exposed on #PineDio Stack's GPIO Connector ... So we use GPIO 5 to Shadow the CS Pin

https://github.com/lupyuen/bl_iot_sdk/blob/3wire/customer_app/pinedio_st7789/pinedio_st7789/display.c#L504-L534

#BL604 doesn't seem to be transmitting anything to ST7789 on SPI MOSI (GPIO 17) ... Let's try a different pin for MOSI

Yep #BL604 MOSI works if we switch to GPIO 4 ... So what's wrong with GPIO 17? 🤔

Which is super strange because GPIO 4 is supposed to be MISO on #BL604 ... Not MOSI! 🤔

https://lupyuen.github.io/articles/spi#spi-data-pins-are-flipped

GPIO 4 works as MOSI but not GPIO 17 ... What if we connect GPIO 4 to 17? Nope still nothing on the #PineDio Stack ST7789 Display 🤔

@JF discovered this function from #BL604 IoT SDK that swaps MISO and MOSI ... Let's test GLB_Swap_SPI_0_MOSI_With_MISO

https://github.com/lupyuen/bl_iot_sdk/blob/3wire/customer_app/pinedio_st7789/pinedio_st7789/demo.c#L53-L75

Yep MISO and MOSI are now swapped! This matches the SPI Pin Definitions in #BL604 Reference Manual ... So from now on we'll always call GLB_Swap_SPI_0_MOSI_With_MISO

https://github.com/lupyuen/bl_iot_sdk/blob/3wire/customer_app/pinedio_st7789/pinedio_st7789/demo.c#L53-L75

#BL604 GPIO 17 is now free from the MOSI Curse! But nothing appears on #ST7789 Display 🤔

https://github.com/lupyuen/bl_iot_sdk/blob/3wire/customer_app/pinedio_st7789/pinedio_st7789/demo.c#L53-L75

Debugging SPI on BL604 for the @thepine64
#PineDio Stack with @lupyuen : Why are MOSI and MISO swapped? And will GLB_Swap_SPI_0_MOSI_With_MISO() help us?