Nios/uartread

Write a function to read a string (terminated with character '\n', or 0x0d) from a UART device and writes that string into memory. You will need to poll the UART device to read each character as it becomes available. Replace the \n character with a null character in the output string. Return the length of the string.

unsigned int uartgets (char *output);

You are provided a function to read the status of the UART:

unsigned int read_uart();

The 32-bit word includes information about the state of the UART and the received character, if available:

bit [15]: 1 if the character in bits [7:0] is valid. If valid, the character is also dequeued from the UART so that the next read will return the next character, if available. If not valid, bits [7:0] in the word are undefined. You need to poll the device to read each character in the string.
bits [7:0]: The character received from the UART, if there was a character available.

To make this problem easier, read_uart only clobbers r2 (the return value) (and ra, of course).

Expected solution length: Around 20 lines.

Sample Input

"Hello world"

Sample Output

r2=11

.data
Out: .skip 256	# Reserve some space for output

.text
#read_uart:	# This may be useful for debugging
	movia r2, 0xff201000
	ldwio r2, 0(r2)
	ret

.global _start
_start:
	movia sp, 0x04000000    # Initialize SP for debugging.
	movia r4, Out    # Use Out as the output string
	call uartgets
1:	br 1b    # Done

uartgets:

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