If don't know if this is an issue that anyone cares about. I am also
not sure what the best way to solve it is either. I just thought I
would issue a pull request with this commit to bring the issue to light
and show a possible solution that I have tested on my mbed-1768 device.
Previously the serial_putc() API didn't make any use of the Tx FIFO
since the serial_writable() API it utilizes only returns true when the
FIFO is completely empty. This is due to the fact that the THRE bit of
the UART's LSR (Line Status Register) only goes high when the whole
FIFO is empty.
I noticed this when doing some performance testing with the network
stack. I went from calling printf() to output 3 bytes every 10 seconds
(with packet drop stats) to instead output 4 bytes every 10 seconds.
I thought these should easily fit in the 16 byte FIFO but outputting
one extra byte caused an additional three 550 byte UDP packets to be
dropped. This should only happen if the additional character being
sent to the UART was taking away extra CPU cycles from the network
stack.
My solution is to keep track of the number of bytes that have been
placed in the Tx FIFO since it was last detected as being completely
empty (via the THRE bit). Only once this count hits 16 does the code
then block, waiting for the THRE bit to go high. Each time the THRE
bit does go high, the count is reset to 0 again and it is incremented
for each byte that is loaded into the THR.
Because the LPC81X HAL implementation calls error(), which in turn calls
fprintf(), quite a bit of code is added to the image, which is not a good
idea on such resource constrained targets.
The new RawSerial class is a simple wrapper over the serial HAL that can
be safely used from an interrupt handler.
Interrupt chaining code was removed from InterruptIn, Serial and Ticker
because it caused lots of issues with the RTOS. Interrupt chaining is
still possible using the InterruptManager class.
Because CT32B1 (P1_1, P1_2 and P1_3) is used by us_ticker.c for wait and ticker function. Since wait/ticker is commonly used by mbed code and I decided CT32B1 of LPC11XX should only be used for this function, not for PwmOut.
P1_6 and P1_7 are used by UART (USBTX/USBRX) and I think they should not be assigned to other function.
DEVICE_STDIO_MESSAGES is the only #define in device.h that is being used in the library as #ifdef rather than #if. This is misleading since setting it to 0 will not disable including the <stdio.h> libraries.
A recent commit, 43acaa4166, to get _sbrk() to build successfully for
LPC2368 broke the Cortex-M implementation. __get_MSP() isn't ever
defined as a macro, it is an inline function. This means that the
code would always be compiled to use SP instead of MSP on Cortex-M
parts. I switched the code to instead use the TARGET_ARM7 define
to choose which stack pointer to utilize.
I tested this fix by making sure that the LPC2368 version of the mbed
SDK would still build successfully with the Python scripts and that the
NET1 test still built and ran successfully on my mbed-LPC1768 device.
Bogdan Marinescu
Joris Aerts
0xc0170
Andreas Rebert
pbrier
Emilio Monti
Bogdan Marinescu
Adam Green
Joe Turner
Bogdan Marinescu
Michael Conners
Toyomasa Watarai
dinau