从微控制器发送命令以通过SPI显示并接收结果

Question

Ok, this question might be a little wide as I don't really know where to start with all this. I'll try to be clear.

I have a mobile phone display with a known display driver for wich I have the data sheet. This display will communicate with a micro controller (msp430g type) over SPI.

Some of the commands sent to the display does not yield a response but some do, the response might be several "bytes" (9 bits of data).

I first thought that I should have a fifo buffer to which the microcontroller fed commands so that the micro could do other stuff while the command is being shifted out. But I get the feeling that would "disconnect" the command from the possible response in the case where there is a response. And I don't know how to deal with that.

My second thought was to have all commands as functions that did the (write->[read*x]) that the command in question would need. But that feels like I will have the micro standing around waiting for the SPI interface way to much.

What is the "normal" thing to do in this case? I guess there are many answers but I'm sure a lot of code has been written that uses some interface to communicate with some device but do other stuff while the interface is "working".

If there is anything vague about what I'm trying to do, please just let me know and I'll try to clarify.

Answer 1

SPI is master-slave, so to Rx from the slave (I'm assuming the display will be the slave) you need to transmit a dummy byte of data (so the master is waggling the clock line) and you should get the Rx data clocked in on your Rx (In/Rx/MISO) pin.

If there is a hardware SPI interface that can handle this autonomously then you can leave it all to work in the background & should get an interrupt when it's finished.

I can't speak for the MSP but on the Coldfire the SPI hardware can be loaded with some stuff to Tx/Rx and will go and do it, in your example you would append a dummy byte to the end of the Tx data and the reply byte would then be in the last slot in the RX buffer when the "ready" interrupt happened.

Answer 2

To schedule the reads and writes in an efficient way, I would recommend the use of interrupts. The MSP430 has an interrupt for both when a byte gets sent, and when a byte has been received. When the interrupt fires, load the next byte to be sent (for tx), or store the received byte (for rx). When your command has been sent, you can set a flag for getting a response if you expect one. When you have received a reply you can set a flag for your main loop to process the response.