Without free-up of peripheral pins, peripheral pins of the same peripheral may
share by multiple ports after port iteration, and this peripheral may fail with
pin interference.
Better IP initialization sequence:
1. Configure IP pins
2. Select IP clock source and then enable it
3. Reset the IP (SYS_ResetModule)
NOTE1: IP reset takes effect regardless of IP clock. So it doesn't matter if
IP clock enable is before IP reset.
NOTE2: Non-configured pins may disturb IP's state, so IP pinout first and then
IP reset.
NOTE3: IP reset at the end of IP initialization sequence can cover unexpected
situation.
With support for checking H/W UART initialized or not, we can simplify stdio management:
1. When serial_init(&stdio_uart) calls in, just set the 'stdio_uart_inited' flag.
2. When serial_free(&stdio_uart) calls in, just clear the 'stdio_uart_inited' flag.
Except above, we needn't make special handling with 'stdio_uart'.
The same H/W UART may be shared by multiple serial_t objects. This fix tries to avoid
re-configuring the same H/W UART in serial_init() when there are multiple serial_t
objects constructed. To re-configure UART, call serial_baud() and serial_format()
explicitly. This can avoid confusion when e.g. a newly constructed serial_t object
changes baudrate unexpectedly in serial_init().
Serial implementation uses different vector handlers for sync/async calls respectively. The issue can be reproduced with the following flow:
1. Register sync mode callback with Serial.attach().
2. Sync call with Serial.putc()/getc().
3. Change to async call with Serial.write()/read().
4. Change back to sync call with Serial.putc()/getc().
Now, vector handller is still for async mode, not for sync mode.
To fix it:
1. Introduce internal function serial_enable_interrupt() for both sync/async vector handler enable/disable.
Original HAL function serial_irq_set() is reduced to call it for sync mode vector handler enable/disable.
2. Introduce internal function serial_rollback_interrupt() to roll back sync mode vector handler at end of async transfer.
Chun-Chieh Li
Russ Butler