SPI returning "FF" when BUS is shared with e-ink display

[DarkZeros]

Hi I have a ESP32-S3 board that I am building, with e-ink and SX1262 (RA01-SH module).
The code seems to work fine if the first thing I run on the board is the LORA part:

IE:

  ESP_LOGE("lora", "starting");
  const SPISettings Lora::kSpiSettings{10'000'000, MSBFIRST, SPI_MODE0};
  SX1262 Lora::kRadio = new Module(HW::Lora::Cs, HW::Lora::Dio1, HW::Lora::Rst, HW::Lora::Busy, SPI, kSpiSettings);
  SPI.begin(HW::Lora::Sck, HW::Lora::Miso, HW::Lora::Mosi, HW::Lora::Cs);
  kRadio.begin(434.0, 125.0, 9, 7, 0x12, 10, 8, 0, false);
  kRadio.sleep();
  SPI.end();

E (118) lora: starting
[0.095884] RLB_DBG:
RadioLib Info
Version: "7.1.2.0"
Platform: "ESP32"
"May 16 2025" "16:45:48"
[0.108007] RLB_DBG: Found SX126x: RADIOLIB_SX126X_REG_VERSION_STRING:
[0.110183] RLB_DBG: 00000320: 53 58 31 32 36 31 20 56 32 44 20 32 44 30 32 00 SX1261 V2D 2D02.
[0.118398] RLB_DBG:
[0.120309] RLB_DBG: M SX126x

However if I run some display updates, go to deep sleep the ESP32, and wake-up, execute the same code, I get this:

RadioLib Info
Version: "7.1.2.0"
Platform: "ESP32"
"May 16 2025" "16:45:48"
[1.069516] RLB_DBG: SX126x not found! (1 of 10 tries) RADIOLIB_SX126X_REG_VERSION_STRING:
[1.069984] RLB_DBG: 00000320: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ................
[1.074757] RLB_DBG: Expected string: SX1261
[2.098023] RLB_DBG: SX126x not found! (2 of 10 tries) RADIOLIB_SX126X_REG_VERSION_STRING:
[2.098409] RLB_DBG: 00000320: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ................
[2.103212] RLB_DBG: Expected string: SX1261

The SCK/MOSI pins of the 2 devices are shared, but BUSY/MISO/DC/CS/NSS are separate.
If I finish the SPI bus with end() before starting the other one, then it seems to work fine, but that completely breaks the multithreading of both devices.

I am unable to figure out what can be wrong to be honest....

Any help is appreciated, since I do not have enough available GPIO in my project to have separate bus pins for each one of them.

[DarkZeros]

Some extra info.

It seems that if I set up the SPI bus for the Display with the lora MISO one the communication now works fine for most packets.... I am not understanding this? If the SPI bus global and the kSpiSettings local for each of them?

I will try that and likely close this discussion, stupid on my side.

[DarkZeros]

My current explanation is that when one sets up the bus if breaks the other one.
I should probably set up one global bus, same settings. But if I do that, the HwCs feature of SPI can´t be used, since I have multiple devices with different CS on the same bus.

[DarkZeros]

Ok yes that seems to work fine. I need to investigate it more but both seems to be running properly on SW CS mode.

[jgromes]

The SCK/MOSI pins of the 2 devices are shared, but BUSY/MISO/DC/CS/NSS are separate.

That's not how SPI bus works. The SCK, MISO and MOSI must all be shared among the devices. Otherwise, how would your ESP32 know that it is supposed to use different MISO pin for SX1262?

[DarkZeros]

The confusion comes to me because the display does not have a MISO pin, therefore i was initializing the bus 2 times. One with MISO correctly (for lora) and one without for the display (wrong).

The bus did work for lora still, but was receiving FF since the MISO pin was deinitialized.

I think now i know why it didnt work. And managed to make it work properly.