UARTkstr

Purpose

String IO procedures
HW-buffered (FIFO)

Notes

Kernel is required.

Description

GetString

Uses interrupts to read the received data into the string buffer provided to GetString.¹
Since the RPx MCUs only provide one interrupt wired to the NVIC for all UART interrupts, there’s one handler for two interrupts:
- as soon as the receive FIFO level has reached its trigger level, its contents are copied to the string buffer;
- if no data is received for a specific amount of clock cycles, the timeout interrupt handling copies the remaining data to the string buffer.
The interrupt handler disables both interrupts when done.
The kernel thread initiates the above mechanics, and then awaits the disabling of the interrupts.
Since we’re using kernel-v1 here, the interrupt handler cannot put the waiting thread directly onto the run-queue.

FIFO Threshold

Depending on the overall interrupt set-up and configuration of the program, the FIFO threshold that triggers the corresponding interrupt can be chosen differently. Either we opt for more frequent interrupts, but with a shorter run-time using a lower threshold, or less frequent ones with a longer run-time with a higher threshold.

The default is 4/8, ie. 16 FIFO entries. With this configuration, input up to 15 characters, eg. for numbers, is handled exclusively by the timeout interrupt.

Repository

UARTkstr.mod