SPI CS toggling after each byte

[Desiderius]

Hello all,

I have a quite unorthodox screen that requires that the SPI CS line comes back to 1 after each Byte.

I have a bit-banged solution that work well but I would prefer to be able to use DMA and hardware SPI.

When I tried I haven't found a suitable solution in the SDK.

Does Anyone have an idea?

Thank you in advance.

Best regards

Em

[ESP_Sprite]

That is a strange requirement indeed... to be honest, I'm not sure if our hardware can do this. What display is this, if I may ask?

If you really need this as you describe, I can see two options:
- Use the I2S peripheral. You'll probably have to write your own driver, but I *think* it can be configured to do single transfers and then stop. You can use the WC signal as your toggling CS in this case; configure it so the left channel is your output byte and the right channel (when ws is high) is a constant.
- Use an external binary counter IC, connect the clk to the SPI clock output on the ESP32 and the divide-by-eight output to the CS input of the LCD.

[Desiderius]

That is a strange requirement indeed... to be honest, I'm not sure if our hardware can do this. What display is this, if I may ask?

Sure, I'm using e-Paper screen used for electronic shelf label. the driver is made by a company named ultrachip from Taiwan.
The timing is like that.

Capture d’écran 2017-04-13 à 11.23.24.png (107.8 KiB) Viewed 6180 times

From my point of view I don't really understand the use of a hardware CS implementation if the CS signal is so slow and can be easily made using a GPIO.

If you really need this as you describe, I can see two options:
- Use the I2S peripheral. You'll probably have to write your own driver, but I *think* it can be configured to do single transfers and then stop. You can use the WC signal as your toggling CS in this case; configure it so the left channel is your output byte and the right channel (when ws is high) is a constant.
- Use an external binary counter IC, connect the clk to the SPI clock output on the ESP32 and the divide-by-eight output to the CS input of the LCD.

I like the I2C idea I will see if it can be implemented likewise. For the moment the bit-bang implementation can go up to 2Mb/s but take 100% of a processor during the image transfers.

Thank you for your time and best regards

Em

[ESP_Sprite]

The thing is that you can get the SPI hardware to set specific CS timings, depending on your type of transfer. GPIO-based CS timings can be fairly random, depending on what the CPU is doing.

The CS signal indeed is pretty weird... are you 100% sure you *must* make the CS line high between every byte? Most 9-bit SPI slave implementations will just start on a next byte after the 9th bit has come in.