Now we shouldn't experience wait cycles in i2c_write() during
typical display writes any longer. It should also distribute CPU
load of display writes a lot better.
Previously writing a line of text to the display would take
almost as long as it took to actually send it to the display,
because the I2C queue could hold only one transmission, which
effectively meant only one character. This could hold the main
loop for several milliseconds.
Now we queue characters, send them one by one, and return to the
main loop in between.
This costs 160 bytes program memory. Only 18 bytes RAM, because
the I2C queue was reduced accordingly. Now:
Program: 24456 bytes
Data: 1543 bytes
EEPROM: 32 bytes
As we usually talk to one device only, there's not much point in
carrying around the address all the time. Surprise, this saves
only 16 bytes binary size despite of heavy usage.
This removes the need to write in full blocks, so data can be
sent from loops and/or program memory.
This capability allows to clear the screen without too much
effort, see i2c_test.c.
Still two weaknesses left:
- Transmission end is currently detected by ringbuffer becoming
empty, so delays are needed to make sure a transmission is
completed before the next one is sent to the buffer.
- Error handling is still only half existent. Any error on the
bus will stop I2C entirely. A recovery strategy is required.
Sizes show, taking into account the additional screen clearing
code, no significant change:
FLASH : 23216 bytes
RAM : 2052 bytes
EEPROM : 32 bytes
Naively restarting I2C immediately is certainly not the solution
and just leads to an interrupt flood. As I2C is currently meant
to drive displays, where successful data transmission isn't
crucial, we now simply stop transmission on errors.
This saves another 80 bytes binary size:
FLASH : 23094 bytes
RAM : 2051 bytes
EEPROM : 32 bytes
This commit squashes in some fixes found after debugging on the
topic branch. Test code by Traumflug, collected from Ruslan's
code on the topic branch.
Before, same as now without I2C:
FLASH : 22408 bytes
RAM : 1393 bytes
EEPROM : 32 bytes
Now with I2C:
FLASH : 23224 bytes
RAM : 2057 bytes
EEPROM : 32 bytes
This totals to some 800 bytes with a whole lot of test code, so
implementation is pretty small :-)
Markus Hitter
Ruslan Popov