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README
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Buffering Notes
===============
Hardware Flow Control
---------------------
Hardware flow control must be enabled in serial drivers in order to
prevent data overrun. However, in the most NuttX serial drivers, hardware
flow control only protects the hardware RX FIFO: Data will not be lost in
the hardware FIFO but can still be lost when it is taken from the FIFO.
We can still overflow the serial driver's RX buffer even with hardware
flow control enabled! That is probably a bug. But the workaround solution
that I have used is to use lower data rates and a large serial driver RX
buffer.
Those measures should be unnecessary if buffering and hardware flow
control are set up and working correctly.
RX Buffer Size
--------------
The Zmodem protocol supports a message that informs the file sender of
the maximum size of dat that you can buffer (ZRINIT). However, my
experience is that the Linux sz ignores this setting and always sends file
data at the maximum size (1024) no matter what size of buffer you report.
That is unfortunate because that, combined with the possibilities of data
overrun mean that you must use quite large buffering for Zmodem file
receipt to be reliable (none of these issues effect sending of files).
Buffer Recommendations
----------------------
Based on the limitations of NuttX hardware flow control and of the Linux
sz behavior, I have been testing with the following configuration
(assuming UART1 is the Zmodem device):
1) This setting determines that maximum size of a data packet frame:
CONFIG_SYSTEM_ZMODEM_PKTBUFSIZE=1024
2) Input Buffering. If the input buffering is set to a full frame, then
data overflow is less likely.
CONFIG_UART1_RXBUFSIZE=1024
3) With a larger driver input buffer, the Zmodem receive I/O buffer can be
smaller:
CONFIG_SYSTEM_ZMODEM_RCVBUFSIZE=256
4) Output buffering. Overrun cannot occur on output (on the NuttX side)
so there is no need to be so careful:
CONFIG_SYSTEM_ZMODEM_SNDBUFSIZE=512
CONFIG_UART1_TXBUFSIZE=256
Using NuttX Zmodem with a Linux Host
====================================
Sending Files from the Target to the Linux Host PC
--------------------------------------------------
The NuttX Zmodem commands have been verified against the rzsz programs
running on a Linux PC. To send a file to the PC, first make sure that
the serial port is configured to work with the board (Assuming you are
using 9600 baud for the data transfers -- high rates may result in data
overruns):
$ sudo stty -F /dev/ttyS0 9600 # Select 9600 BAUD
$ sudo stty -F /dev/ttyS0 crtscts # Enables CTS/RTS handshaking
$ sudo stty -F /dev/ttyS0 # Show the TTY configuration
Start rz on the Linux host (using /dev/ttyS0 as an example):
$ sudo rz </dev/ttyS0 >/dev/ttyS0
You can add the rz -v option multiple times, each increases the level
of debug output. If you want to capture the Linux rz output, then
re-direct stderr to a log file by adding 2>rz.log to the end of the
rz command.
NOTE: The NuttX Zmodem does sends rz\n when it starts in compliance with
the Zmodem specification. On Linux this, however, seems to start some
other, incompatible version of rz. You need to start rz manually to
make sure that the correct version is selected. You can tell when this
evil rz/sz has inserted itself because you will see the '^' (0x5e)
character replacing the standard Zmodem ZDLE character (0x19) in the
binary data stream.
If you don't have the rz command on your Linux box, the package to
install rzsz (or possibily lrzsz).
Then on the target (using /dev/ttyS1 as an example).
> sz -d /dev/ttyS1 <filename>
Where filename is the full path to the file to send (i.e., it begins
with the '/' character). /dev/ttyS1 or whatever device you select
*MUST* support Hardware flow control in order to throttle therates of
data transfer to fit within the allocated buffers.
Receiving Files on the Target from the Linux Host PC
----------------------------------------------------
To send a file to the target, first make sure that the serial port on the
host is configured to work with the board (Assuming that you are using
9600 baud for the data transfers -- high rates may result in data
overruns):
$ sudo stty -F /dev/ttyS0 9600 # Select 9600 BAUD
$ sudo stty -F /dev/ttyS0 crtscts # Enables CTS/RTS handshaking
$ sudo stty -F /dev/ttyS0 # Show the TTY configuration
Start rz on the on the target. Here, in this example, we are using
/dev/ttyS1 to perform the transfer
nsh> rz -d /dev/ttyS1
/dev/ttyS1 or whatever device you select *MUST* support Hardware flow
control in order to throttle therates of data transfer to fit within the
allocated buffers.
Then use the sz command on Linux to send the file to the target:
$ sudo sz <filename> t </dev/ttyS0 >/dev/ttyS0
Where <filename> is the file that you want to send.
The resulting file will be found where you have configured the Zmodem
"sandbox" via CONFIG_SYSTEM_ZMODEM_MOUNTPOINT.
You can add the az -v option multiple times, each increases the level
of debug output. If you want to capture the Linux rz output, then
re-direct stderr to a log file by adding 2>az.log to the end of the
rz command.
If you don't have the az command on your Linux box, the package to
install rzsz (or possibily lrzsz).
STATUS
2013-7-15: I have tested with the configs/olimex-lpc1766stk
configuration. I have been able to send large and small files with
the sz command. I have been able to receive small files, but there
are problems receiving large files: The Linux SZ does not obey the
buffering limits and continues to send data while rz is writing
the previously received data to the file and the serial driver's RX
buffer is overrun by a few bytes while the write is in progress.
As a result, when it reads the next buffer of data, a few bytes may
be missing (maybe 10). Either (1) we need a more courteous host
application, or (2) we need to greatly improve the target side
buffering capability!
My thought now is to implement the NuttX sz and rz commands as
PC side applications as well. Matching both sides and obeying
the handshaking will solve the issues. Another option might be
to fix the serial driver hardware flow control somehow.
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