From b53dd752258b14a2449681e4c572d83dafb805ca Mon Sep 17 00:00:00 2001
From: Matt Johnston <matt@ucc.asn.au>
Date: Sat, 1 Oct 2022 19:34:46 +0800
Subject: [PATCH] finished ascii art
---
examples/rp/src/bin/usb_serial.rs | 51 ++++++++++++++++++++-----------
1 file changed, 34 insertions(+), 17 deletions(-)
diff --git a/examples/rp/src/bin/usb_serial.rs b/examples/rp/src/bin/usb_serial.rs
index 17dc04f4..c976bbec 100644
--- a/examples/rp/src/bin/usb_serial.rs
+++ b/examples/rp/src/bin/usb_serial.rs
@@ -107,25 +107,42 @@ async fn run<'d, P: Pin>(pin: &mut Flex<'d, P>, syst: &mut SYST) -> Result<(), D
cortex_m::asm::delay(1200);
pin.set_as_input();
pin.set_pull(Pull::Down);
+ // Get it near the threshold to begin.
while pin.is_high() {}
});
let mut up_x = 1u32;
let mut down_x = 1u32;
-
/*
- |prev | |
- |iter | |
- | | |
- . |
- . . | .
- . . | . .
- . . | . .
+ _ still pullup, =up_x
+ t3 t4 t1 t2 /
+ |prev |pulldn |still | pullup| /
+ |iter |active |pulldn,| active| / | pulldn active, etc
+ | |=t_down|=down_x| =t_up | o | measuring next t_down, etc...
+ | . | | | |
+ . . | | | .
+ . . | | | . .
+ . . | | | . .
.---------------.---------------.-----------.------ GPIO threshold. Probably isn't really flat.
. . .
. .
. .
.
+
+ The GPIO pin is attached to a capacitor to ground. 0.1uF used for experiment.
+
+ The GPIO pin is left as input and is driven low/high with pulldown/pullup
+ resistors. The time taken to reach logical low/high is measured. The pulldown/pullup
+ resistor is left on for a further time down_x/up_x, which intends to drive
+ the voltage further so that a useful time can be measured for the next t_up/t_down
+ cycle.
+
+ The down_x/up_x overshoot cycle times are doubled each iteration and add in the measured time,
+ amplifying noise captured in t_down/t_up measurements.
+
+ down_x/up_x time is kept within a sensible range with modulo.
+
+ The random output is t_down and t_up time.
*/
loop {
@@ -162,15 +179,15 @@ async fn run<'d, P: Pin>(pin: &mut Flex<'d, P>, syst: &mut SYST) -> Result<(), D
// It calculates the next overshoot #cycles.
// `prev` is the #cycles returned from last step(), `meas` is the time
// taken for the return to centre value (which is targetting `T`).
- // eg `up_x = step(up_x, down);`
+ // eg `up_x = step(up_x, t_down);`
let step = |prev: u32, meas: u32| {
- // doubling step.
+ // Doubling step.
// x[n] = 2*x[n-1] + meas
let v = prev*2 + meas;
// modulo to sensible range
- if v > UPRANGE {
- LOWRANGE + (v % (UPRANGE - LOWRANGE))
+ if v > HIGH_OVER {
+ LOW_OVER + (v % (HIGH_OVER - LOW_OVER))
} else {
v
}
@@ -192,24 +209,24 @@ async fn run<'d, P: Pin>(pin: &mut Flex<'d, P>, syst: &mut SYST) -> Result<(), D
if i % 2 == 0 {
down_x = step(down_x, t_up);
} else {
- // TODO: keep `up` as our random output
+ // TODO: keep `t_up` as our random output
}
cortex_m::asm::delay(up_x);
pin.set_pull(Pull::Down);
syst.clear_current();
- let t1 = SYST::get_current();
+ let t3 = SYST::get_current();
while pin.is_high() {}
- let t2 = SYST::get_current();
+ let t4 = SYST::get_current();
let t_down = t1 - t2;
if i % 2 == 0 {
up_x = step(up_x, t_down);
} else {
- // TODO: keep `down` as our random output
+ // TODO: keep `t_down` as our random output
}
cortex_m::asm::delay(down_x);
- if (BUF_START..BUF_START+BUF).contains(i) {
+ if (BUF_START..BUF_START+BUF).contains(&i) {
let n = i - BUF_START;
ups[n] = t_up;
upx[n] = up_x;
--
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