fix and improve e220 driver #1
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変更いただいた箇所は一旦取り込むことでよいと考えたため、 merge します。 |
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以下はコメントで TODO として積んだ。
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akif999
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Jul 7, 2023
This is implemented in inline assembly using machine.CPUFrequency() to
know how long a single CPU cycle takes. As long as it is called with a
constant duration, it should be fully inlined and all values can be
const-propagated resulting in very tight inline assembly.
For example, when I convert i2csoft to use this delay function, the
entire delay function compiles to something like this:
8784: movs r6, tinygo-org#100
8786: mov r0, r6
8788: nop
878a: nop
878c: nop
878e: nop
8790: nop
8792: subs r0, #1
8794: bne 0x8788
That means that all the math to calculate the number of cycles is
entirely optimized away (in this case, to 100 loops).
I ran the example on a few boards to see how well it works:
| board | 100ms wait | CPU core
|-----------------------|------------|------
| microbit | 121.6ms | Cortex-M0 so it has 12% overhead
| circuitplay-express | 100.1ms | Cortex-M0+ so it is cycle accurate
| pico | 100.2ms | Cortex-M0+
| pyportal | 100.3ms | Cortex-M4
| circuitplay-bluefruit | 125.8ms | Cortex-M4
| esp8266 | 125.1ms |
This shows that there is some loop overhead because of conservative
estimates, but note that even though there may be a 25% overhead, the
actual overhead per `delay.Sleep()` call is very small. It should be
good enough for software I2C at least, and can potentially be improved
in the future.
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ざっと変更提案を作ってみた。
正しいかは不明。
merge しなくてもよいので、適当に処理してください。
※PR 作ったほうがわかりやすいかな、という事で PR にしています
変更箇所は以下。
あと、残り気づいたところは以下。