From 83532a157bdec93d08a16ea8c69ba7dde4095cbd Mon Sep 17 00:00:00 2001
From: Benjamin Koch <bbbsnowball@gmail.com>
Date: Sat, 13 May 2023 06:53:47 +0200
Subject: [PATCH] implement recovery for bus errors
I don't expect that we will need it but it is good practice to do it.
---
firmware/rust1/src/bin/heizung.rs | 31 +++++++++++++++++++++++++++++--
1 file changed, 29 insertions(+), 2 deletions(-)
diff --git a/firmware/rust1/src/bin/heizung.rs b/firmware/rust1/src/bin/heizung.rs
index 2ce1775..bb32d66 100644
--- a/firmware/rust1/src/bin/heizung.rs
+++ b/firmware/rust1/src/bin/heizung.rs
@@ -151,8 +151,35 @@ async fn i2c_write_zero_bytes<SCL: gpio::Pin, SDA: gpio::Pin, const FREQ : u64>(
scl.set_low();
Timer::after(delay).await;
- if sda.is_low() || scl.is_low() {
- return Err(Abort(ArbitrationLoss))
+
+ // abort if SCL is stuck low
+ handle_clock_stretching(&mut scl).await?;
+
+ // handle SDA being stuck low
+ // (This can happen for very simple I2C devices that only use SCL and don't have any other clocks that
+ // they can use to handle timeouts, e.g. simple port expanders.)
+ if sda.is_low() {
+ // I think I have read that DW_apb_i2c does nine clocks. This seems resonable so let's do the same.
+ for _ in 0..9 {
+ scl.set_as_output();
+ Timer::after(delay).await;
+ scl.set_as_input();
+ Timer::after(delay).await;
+
+ if sda.is_high() {
+ break;
+ }
+ }
+
+ if sda.is_low() || scl.is_low() {
+ // There is isn't much that we can do here. A start condition would reset the state but we cannot
+ // generate it while one of the lines is stuck low.
+ return Err(Abort(ArbitrationLoss))
+ }
+
+ // SDA is high, again. Good. We will generate a start condition soon. This should abort any
+ // partial transfers that some devices might think are ongoing. We have already waited for half
+ // a clock so we are good to go.
}
let result = i2c_write_zero_bytes_middle_part::<_, _, FREQ>(addr, delay, &mut scl, &mut sda).await;
--
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