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mod-spi.md

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SPI Controller

The SPI peripheral of the EZRadioPRO handles the SPI API communication:

  • Receiving argument stream
  • Controlling CTS status and pin
  • Sending the reply stream

The SPI peripheral handles the following SPI API commands autonomously without invoking the 8051 MCU:

  • cmd:READ_CMD_BUFF to send reply stream
  • cmd:FRR_A_READ - cmd:FRR_D_READ to read fast response registers (FRR) A-D
  • cmd:WRITE_TX_FIFO to write bytes into the transmit FIFO
  • cmd:READ_RX_FIFO to read bytes from the receive FIFO

SPI communication

After receiving a SPI API command that is not handled by the SPI peripheral itself, the MCU will receive a COMMAND interrupt (vector INT_COMMAND, 0x001F).

The SPI API argument stream is passed to the 8051 in the registers reg:CMD_BUFF0 - reg:CMD_BUFF15, starting with CMD in reg:CMD_BUFF0. The length of the argument stream is available in reg:SPI_CMD_STATUS:CMD_COUNT.

The reply stream is also passed through reg:CMD_BUFF0 - reg:CMD_BUFF15, excluding the CTS byte. I.e. index 0x01 of the reply stream is written to reg:CMD_BUFF0.

The 8051 indicates completion of an SPI API command by setting reg:SPI_CMD_STATUS:CMD_BUF_CLEAN.

Command error conditions are signaled by setting reg:SPI_CMD_STATUS:CMD_ERROR.

The register reg:CTS is set to 0xff when the 8051 completed processing of a command and/or is ready for a new command. This is likely the CTS field in the SPI response.

Fast read registers (FRR)

The SPI API commands cmd:FRR_A_READ through cmd:FRR_D_READ provide fast access to arbritrary variables. The 8051 sets the content of FRR A through D by writing to reg:FAST_RES_A through reg:FAST_RES_D.

RX and TX FIFOs

The SPI peripheral processes the commands cmd:READ_RX_FIFO and cmd:WRITE_TX_FIFO without invoking the 8051. The FIFOs are located in RAM and processed by DMA. See mod:SPI_DMA for more information.

EZRadioPRO firmware implementation

In the EZRadioPRO firmware, most commands are processed synchronously within the INT_COMMAND interrupt service routine. The exceptions are cmd:GET_ADC_READING, cmd:IRCAL, cmd:PROTOCOL_CFG and undocumented cmd:WAIT_PROPERTY_PROCESSED (0x1b), which run asynchronously within the main loop.

Custom commands can be added by hooking map.spi_unknown_cmd (0x0132) for synchronous or map.main_loop_unknown_cmd (0x0213) for asynchronous processing (revision C2A/A2A).

If reg:SPI_CMD_STATUS:CMD_ERROR is set when done processing a SPI API command, the firmware will report the CMD_ERROR_COMMAND_BUSY error.