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authorMatthijs Kooijman <matthijs@stdin.nl>2014-04-23 19:23:58 +0200
committerMatthijs Kooijman <matthijs@stdin.nl>2015-01-26 17:03:25 +0100
commit0a6072dccb5e8c278620ce8ae23fdf420dc807f1 (patch)
treece6c8e05905749de2e94d812a40c13b69c8bc6ae /libraries/Wire/examples/SFRRanger_reader/SFRRanger_reader.ino
parent08c3bfdc9fd5da81932ec9e4df0b645c93f2ebdc (diff)
Fix SoftwareSerial timings
Instead of using a lookup table with (wrong) timings, this calculates the timings in SoftwareSerial::begin. This is probably a bit slower, but since it typically happens once, this shouldn't be a problem. Additionally, since the lookup tables can be removed, this is also a lot smaller, as well as supporting arbitrary CPU speeds and baudrates, instead of the limited set that was defined before. Furthermore, this switches to use the _delay_loop_2 function from avr-libc instead of a handcoded delay function. The avr-libc function only takes two instructions, as opposed to four instructions for the old one. The compiler also inlines the avr-libc function, which makes the timings more reliable. The calculated timings directly rely on the instructions generated by the compiler, since a significant amount of time is spent processing (compared to the delays, especially at higher speeds). This means that if the code is changed, or a different compiler is used, the calculations might need changing (though a few cycles more or less shouldn't cause immediate breakage). The timings in the code have been calculated from the assembly generated by gcc 4.8.2 and gcc 4.3.2. The RX baudrates supported by SoftwareSerial are still not unlimited. At 16Mhz, using gcc 4.8.2, everything up to 115200 works. At 8Mhz, it works up to 57600. Using gcc 4.3.2, it also works up to 57600 at 16Mhz and up to 38400 at 8Mhz. Note that at these highest speeds, communication works, but is still quite sensitive to other interrupts (like the millis() interrupts) when bytes are sent back-to-back, so there still are corrupted bytes in RX. TX works up to 115200 for all combinations of compiler and clock rates. This fixes #2019
Diffstat (limited to 'libraries/Wire/examples/SFRRanger_reader/SFRRanger_reader.ino')
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