## Summary

SPI Poll Send `bl602_spi_poll_send()` doesn't send any SPI Data because it doesn't enable SPI Master and it doesn't clear the SPI FIFO. Also it hangs because it loops forever waiting for the FIFO.

We fix this problem by moving the code that enables SPI Master and clears the FIFO, from SPI Poll Exchange `bl602_spi_poll_exchange()` to SPI Poll Send. (Note that SPI Poll Exchange calls SPI Poll Send)

[More Details Here](https://github.com/lupyuen/st7789-nuttx#fix-spi-send)

## Impact

This problem affects all NuttX Drivers that call `SPI_SEND()` on BL602, including the ST7789 Display Driver.

Previously `SPI_SEND()` didn't send any SPI Data and never returns, because it loops forever waiting to receive data.

Now `SPI_SEND()` sends data and returns correctly.

[More Details Here](https://github.com/lupyuen/st7789-nuttx#fix-spi-send)

## Testing

We tested the modified SPI Poll Send with NuttX ST7789 Driver and a Logic Analyser on PineCone BL602:

-  [Testing with Logic Analyser](https://github.com/lupyuen/st7789-nuttx#fix-spi-send)

We also tested LVGL with ST7789 on PineCone BL602:

-  [Testing with LVGL](https://github.com/lupyuen/st7789-nuttx#run-lvgl-demo)

As for the modified SPI Poll Exchange, we tested with Semtech SX1262 SPI Transceiver on PineCone BL602:

-  [Testing SPI Poll Exchange](https://github.com/lupyuen/incubator-nuttx/releases/tag/release-2022-03-25)