High-Speed SPI Communication for Arduino Nano 33 BLE Sense

1. Motivation

The reason why we have to develop our own low-level driver (or API) for nano 33 is because the unstable message communication while using official API:


Figure 1. Result from receiver. 

As Figure 1. shows, We use the official API to send the message 'I hope everything goes well' several times, but the receiver shows an inconsistent result. When we slow down the transmission speed, the problem solved. However, the lower speed is not acceptable for many use case.

That is why we have to build a stable & fast SPI API for Arduino Nano 33 BLE Sense. 

2. Basic Principle of SPI



3. Registers of nRF52840

Figure 2. Registers




To-Be-Continue...





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High speed data transmission method for Arduino nano 33 ble

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1. Tested flip pin speed of Arduino nano 33 BLE Sense Code:   while ( 1 ){     digitalWrite ( A0,HIGH ) ;     digitalWrite ( A0,LOW ) ; } Figure 1. approx. 426 kHz Why so slow: Control by mbed-OS  2. Tested SPI error at very low speed 34 became 68:  34: 0010 0010 68: 0100 0100 Problem: clock did not align . 3. Develop corrected SPI and test its speed FAILED: With more than 75% error transmission, it will cost at least 4 times. Risk Evaluation: Continuing SPI development by directly setting registers will face two risks: It may take many days, even weeks, to learn and debug the low-level driver for Arduino-nRF register development due to the lack of documents. There is still a risk of the not aligned clock problem. (might make many efforts in vain) 4. Direct operate register NRF_P0 -> DIRSET = 0x FF ;  //P0 lower 8bit = Input Mode while ( 1 ){   NRF_P0 -> OUTSET = 0x FF ;  // P0 lower 8bit = Output High   NRF_P0 -> OUTCLR = 0x FF ;  // P0 lower 8bit = Output Low } Figure
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