Unexpected .in_waiting and .written values #13
Description
code.py:
import time ; time.sleep(3) # wait for serial after reset
import board
import adafruit_pio_uart
def write(size, ch):
print(f'writing {size} bytes of {ch}...', end=" ")
written = u1.write(f'{size * ch}')
time.sleep(1)
print(f'{written=} {} {u2.in_waiting=}')
# two PIO UARTs, connected to each other
# PIO uart rx buffer 8-9 bytes
# u1 will write, u2 will check in_waiting
print("\nWITHOUT hardware flow control\n")
u1 = adafruit_pio_uart.UART(tx=board.GP0, rx=board.GP1)
u2 = adafruit_pio_uart.UART(tx=board.GP4, rx=board.GP5)
# write a chunk of bytes all at once
for size in (4, 5, 6, 7, 8, 9, 10):
# clear the read buffer for each new test
u2.reset_input_buffer()
print(f'busio initial {u2.in_waiting=}')
write(size, "Z")
print(f"{u2.read(16)=}")
print()
# write bytes one at a time
# clear the read buffer for each new test
u2.reset_input_buffer()
print(f'busio initial {u2.in_waiting=}')
write(4, "Y")
write(1, "X")
write(1, "W")
write(1, "V")
write(1, "U")
write(1, "T") # 9th byte
write(1, "S") # 10th byte
write(1, "R") # 11th byte
write(1, "Q") # 12th byte
print(f"{u2.read(16)=}")
u1.deinit()
u2.deinit()
print("\nWITH hardware flow control\n")
u1 = adafruit_pio_uart.UART(tx=board.GP0, rx=board.GP1, cts=board.GP2, rts=board.GP3)
u2 = adafruit_pio_uart.UART(tx=board.GP4, rx=board.GP5, cts=board.GP6, rts=board.GP7)
# write a chunk of bytes all at once
for size in (4, 5, 6, 7, 8): # 9 bytes would block
# clear the read buffer for each new test
u2.reset_input_buffer()
print(f'busio initial {u2.in_waiting=}')
write(size, "A")
print(f"{u2.read(16)=}")
print()
# write bytes one at a time
# clear the read buffer for each new test
u2.reset_input_buffer()
print(f'busio initial {u2.in_waiting=}')
write(4, "B")
write(1, "C")
write(1, "D")
write(1, "E")
write(1, "F")
# write(1, "G") # 9th byte would block
print(f"{u2.read(16)=}")code.py output:
WITHOUT hardware flow control
busio initial u2.in_waiting=0
writing 4 bytes of Z... written=None () u2.in_waiting=4
busio initial u2.in_waiting=0
writing 5 bytes of Z... written=None () u2.in_waiting=5
busio initial u2.in_waiting=0
writing 6 bytes of Z... written=None () u2.in_waiting=6
busio initial u2.in_waiting=0
writing 7 bytes of Z... written=None () u2.in_waiting=7
busio initial u2.in_waiting=0
writing 8 bytes of Z... written=None () u2.in_waiting=8
busio initial u2.in_waiting=0
writing 9 bytes of Z... written=None () u2.in_waiting=8
busio initial u2.in_waiting=1
writing 10 bytes of Z... written=None () u2.in_waiting=8
u2.read(16)=bytearray(b'ZZZZZZZZZ')
busio initial u2.in_waiting=0
writing 4 bytes of Y... written=None () u2.in_waiting=4
writing 1 bytes of X... written=None () u2.in_waiting=5
writing 1 bytes of W... written=None () u2.in_waiting=6
writing 1 bytes of V... written=None () u2.in_waiting=7
writing 1 bytes of U... written=None () u2.in_waiting=8
writing 1 bytes of T... written=None () u2.in_waiting=8
writing 1 bytes of S... written=None () u2.in_waiting=8
writing 1 bytes of R... written=None () u2.in_waiting=8
writing 1 bytes of Q... written=None () u2.in_waiting=8
u2.read(16)=bytearray(b'YYYYXWVUT')
WITH hardware flow control
busio initial u2.in_waiting=0
writing 4 bytes of A... written=None () u2.in_waiting=4
busio initial u2.in_waiting=0
writing 5 bytes of A... written=None () u2.in_waiting=5
busio initial u2.in_waiting=0
writing 6 bytes of A... written=None () u2.in_waiting=6
busio initial u2.in_waiting=0
writing 7 bytes of A... written=None () u2.in_waiting=7
busio initial u2.in_waiting=0
writing 8 bytes of A... written=None () u2.in_waiting=7
u2.read(16)=bytearray(b'AAAAAAAA')
busio initial u2.in_waiting=0
writing 4 bytes of B... written=None () u2.in_waiting=4
writing 1 bytes of C... written=None () u2.in_waiting=5
writing 1 bytes of D... written=None () u2.in_waiting=6
writing 1 bytes of E... written=None () u2.in_waiting=7
writing 1 bytes of F... written=None () u2.in_waiting=7
u2.read(16)=bytearray(b'BBBBCDEF')
Observations:
- Without flow control, 9 bytes can be written then read, even though
in_waitingnever goes above 8. Anything written after 9 bytes is lost. - With flow control, only 8 bytes can be written then read before write blocks, even though
in_waitingnever goes above 7. Any attempt to write after 8 bytes is blocked. - Other ports also have perhaps unexpected
in_waitingbehavior, but those behave consistently and are probably attributable to SDK or hardware buffers. .writtenalways returnsNoneinstead of the number of bytes written.- Unlike
raspberrypiandespressifbusio.UART, PIO UART with flow control does not hang the serial console when write is blocked. Control-c will interrupt the code. - Unlike some other ports'
busio.UART, PIO UART read will drop extra bytes written when the buffer is full, rather than FIFO-ing the bytes in and dropping older bytes.