https:\/\/github.com\/greiman\/ChibiOS-Arduino<\/a>).\n The point is that only the kernel has been ported, not the HAL \n(Hardware Abstraction Layer) part, thus my guess was that a blocking I\/O\n operation would block other tasks, and in particular that it wouldn’t \nbe feasible to read on multiple serial ports.\n<\/p>\n\n\n\nIt turns out this is not the case (for reading multiple serial ports).\n<\/p>\n\n\n\n
First, I should have been more clever, since Serial API (the Serial.read()) has a non-blocking<\/em> semantics (it returns -1 if there is nothing to read).\n<\/p>\n\n\n\nSecond, by examining the Teensy Serial code, I got that (in HardwareSerial.h):\n<\/p>\n\n\n\n
int serial_getchar(void) { \n uint32_t head, tail;\n int c;\n\n head = rx_buffer_head;\n tail = rx_buffer_tail;\n if (head == tail) return -1; \n if (++tail >= RX_BUFFER_SIZE) tail = 0;\n c = rx_buffer[tail];\n rx_buffer_tail = tail;\n return c; \n} <\/code><\/pre>\n\n\n\nAs we can see, there’s nothing blocking there, we’re just making some\n in-memory operations, no loop, nothing. But where does the character in\n the buffer come from ? \n<\/p>\n\n\n\n
The answer is in the uart0_status_isr interrupt routine. I won’t \ncopy it there, but in short, the ISR is called (by the hardware) when \nthere is something to read in the UART, read it bit by bit and returns. \nThe point is there is no polling, nowhere, and a short interrupt masking\n during the reading of the UART data register.\n<\/p>\n\n\n\n
What about writing ? First, after all, writing to the UART \ndoesn’t need to be blocking (if the receiver isn’t ready, that’s its \nbusiness). Furthermore, there are generous yield<\/strong> spreaded through the code, but since I’m not sure yet how it translates with ChibiOs, I’ll have to investigate further.\n<\/p>\n\n\n\n2015-05-13: Is delay a busy loop ?<\/h1>\n\n\n\n
However, using a loop with delay in one task blocks the other one, in spite of a yield in the implementation of delay.\n<\/p>\n\n\n\n
Actually, if two tasks have the same priority, they don’t block \neach other. It means however (with ChibiOs), that a task executing delay\n blocks tasks with lower priority (unlike chThreadSleep).\n<\/p>\n\n\n\n