Resource sharing and locking question

TinyCLR OS
1

Forgive my ignorance on this matter but I want to be sure I start out this project on the right foot.
Two questions:
-If I have multiple devices on an I2C bus (or SPI) and I want to access each those devices with different threads do I need to lock access to the i2c bus? Since TinyCLR is single-threaded, and I assume Read/Write functions block until completion is it necessary?

-Similar question as above but in regards to a memory buffer. I will have a large memory buffer, probably 4KB that will need to be shared by multiple threads. Various threads will be reading/writing data to it, does it need locking.

I guess the bigger question is does a thread always run to completion or Thread.Sleep() with no interrupts? (I guess that’s 3 questions.)

2

We are using locks within our drivers for I2C and SPI. The lock is only on the read/write calls, not on the entire methods.

public void Write(UInt32 data)
        {
            _data[0] = (Byte)(data >> 16);
            _data[1] = (Byte)(data >> 8);
            _data[2] = (Byte)data;
            lock (_socket.LockSpi)
            {
                _bargraph.Write(_data);
            }
        }

The lock is a “per socket” (or rather “per bus”) lock because not all sockets are using the same bus and the lock does not need to block all spi/i2c calls if buses are not the same.

SocketOne.LockSpi = new Object();
SocketTwo.LockSpi = SocketOne.LockSpi;
SocketThree.LockSpi = SocketOne.LockSpi;
SocketFour.LockSpi = new Object();
SocketFive.LockSpi = SocketFour.LockSpi;
SocketSix.LockSpi = SocketFour.LockSpi;

I think it would be safe to use lock as well for your shared memory.

I don’t understand your third question, though.

3

To clarify my 3rd question, or put it a different way. Is there anything that would interrupt a thread mid-process? So if I have a thread reading through an array of 100 elements are there any processes or tasks that would interrupt that before it’s done?

4

No: Unless your thread has sleep or yield somewhere in loop.
Yes: TinyCLR is Rtos OS so yes. But it won’t effect to your thread (software thread).

To be sure you can use lock {} statement and Disable Interrupt.

Disable Interrupt will lock switching task in native. But it is not recommended.
And remember Enable Interrupt back once you are done with the thread.

5

Does TinyClr have a 20ms thread time slice like MF did?

6

Are any of the buses, UART, SPI, I2C, CAN, buffered so that a Send() returns immediately while the underlying OS sends the data out? (I think UART might be but want to understand better.)

7

Correct. I do not think we have changed that but we have that with native threads so things can be slightly different

8

It is still there, I forgot about that, thanks to remind me :))

UART, CAN => Yes. Send() just put data to fifo buffer and return.
SPI, I2C => No.

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