Firmware - PeraZver/Microwavino GitHub Wiki

Firmware is based on Arduino/C++ code that can be found in SW/Firmware.

'Microwavino-basic' example contains basic, user configurable, functionality of the synthesizer. In it, the user can choose multiple options: adjust PLL parameters of MAX2871, control output power, activate/deactivate RF port etc. User can also read out settings of MAX2871. Library written for this example, MAX2871.h contains everything related to MAX2871 operations.

The firmware is made for Teensy LC but is also compatible with Teensy 3.1/3.2.

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Initialization

The code begins with initialization of SPI port and pin mode settings of the Teensy. It makes sure that that all output and input pins are set properly and all chip-enable signals active. Function MAX2871_Init () initializes MAX2871 chip by writing registers 5 to 0, twice. Registers of MAX2871 are 32 bits long, so we need 4 times 8-bit SPI transmission for one register transmission. Function MAX2871_SPI_tx(uint32_t data) handles this transmission.

User interface

When the initialization is completed, program enters the loop mode where it waits for user input from serial terminal. Depending on received character, various functions are executed. For instance, functions where only one character is required, like e, d or g will do simple tasks: enable/disable RF output and read out register content of MAX2871. Other function require more characters to proceed. For instance, rv, rt, or px, where different ADC settings or power outputs are selected. And finally, there are functions that require numbers to be entered, such as Nxa, Fxa, Mxa, Rxa, and Dx. These functions are setting PLL parameters of MAX2871 and output divider. Since the number x can have between 1 to 5 digits, it is necessary to create serial buffer that will store the number from serial input and convert it to integer. This is done in function String2Int(). To avoid large buffers and memory space waste, it is necessary to terminate input with character 'a'. This is how function String2Int() knows user entered desired value. Keep in mind that this doesn't apply to function Dx. This is because divider can only have 1-digit input (from 0 to 7) and serial buffer is not needed there.

Sweep

If Microwave Transmitter is ever going to be used in some real application, frequency sweep functionality is a must-have feature. Frequency is swept by two parameters, N and F. This is implemented in function MAX2871_Sweep(char divider_type, uint16_t a, uint16_t b, uint16_t dt). Function takes arguments divider_type that may be 'N' or 'F', 'a' and 'b' that are lower and upper sweep values, and 'dt' that is time step in milliseconds. From user interface, this function is selected by command s. As before, values for 'a', 'b' and 'dt' must be terminated with character 'a'. For example to sweep paramter F from 100 to 200 in 10ms steps, user must enter 'sF100a200a10a'.