Grant Edwards wrote:
On 2009-02-22, John Nagle <na...@animats.com> wrote:
I've been using PySerial on Windows (Win2000, amusingly) to
drive a Baudot teletype at 45.45 baud. Input and output work,
but there's a delay of about 1 second (!) on the input side
between receiving a character and reporting it to the program.
The UART you're using almost certainly has a receive FIFO.
Normally, the UART doesn't interrupt the CPU to tell it there's
receeve data ready until the FIFO is almost full (eg 12 bytes
present in a 16 byte FIFO).
If the UART has an empty receive FIFO, and it receives a single
character that character goes into the receive FIFO. If data
stops coming in before the rx FIFO threshold is reached, the
UART will wait 40 bit-times...
Ah, 40 bit times. That's the default. And that's the problem.
I thought the accumulation timer was a fixed timer of a few milliseconds.
There is a "disable FIFO" checkbox in Windows 2000. It's hard to
find.
- Log off as user.
- Log on as "administrator"
- Open Control Panel -> System
- Go to "Devices" tab and select "Device manager".
- Open "Ports" in the tree and click on desired COM1 port.
- Click "Advanced" button.
- Set "Receive buffer size" slider to 1.
- Click "Disable FIFO" checkbox.
- Close all the dialogs.
- Reboot. (Yes, it doesn't take effect until the next reboot.)
That fixed the problem. Thanks.
John Nagle
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