SPISettings is set with wrong value for SPI clock speed

[Rotzbua]

Step 1: Describe your environment

• OS version: all
• Arduino IDE version: all
• MFRC522 Library version: 1.1.5 <= x <=1.4.7
• Arduino device: all
• MFRC522 device: all

Step 2: Describe the problem

Observed Results:

• SPI clock speed is not set correctly

Expected Results:

• Do it right.

Relevant Code:

SPI.beginTransaction(SPISettings(SPI_CLOCK_DIV4, MSBFIRST, SPI_MODE0)); // Set the settings to work with SPI bus

Introduces with commit 3c3ffa0 . There are many wrong examples with this code in the internet.

Required is:

SPISettings(uint32_t clock, uint8_t bitOrder, uint8_t dataMode)

SPI_CLOCK_DIV4 does not represent the clock speed. Just a number (between ~0-100). So can not be used for clock.

References

Seems to be measured here: #269 (comment)

Initial #544

Reason arduino/ArduinoCore-mbed#113 (comment)