From f0b7f43c4104ea15c860d557c4a507681cba0d0d Mon Sep 17 00:00:00 2001
From: Daniel Bevenius <daniel.bevenius@gmail.com>
Date: Fri, 9 Sep 2022 14:15:19 +0200
Subject: [PATCH] Use wrapping_sub in update_credit
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
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This commit uses wrapping_sub for subtraction in update_credit.

The motivation for this is that currently the rpi-pico-w example panics
(at least for me) with the following error:

3.825277 INFO  init done
└─ cyw43::{impl#4}::init::{async_fn#0} @ /embassy/cyw43/src/fmt.rs:138
3.825486 INFO  Downloading CLM...
└─ cyw43::{impl#2}::init::{async_fn#0} @ /embassy/cyw43/src/fmt.rs:138
3.841328 WARN  TX stalled
└─ cyw43::{impl#4}::run::{async_fn#0} @ /embassy/cyw43/src/fmt.rs:151
3.845549 ERROR panicked at 'attempt to subtract with overflow', /embassy/cyw43/src/lib.rs:919:16
└─ panic_probe::print_defmt::print @ .cargo/registry/src/github.com-1ecc6299db9ec823/panic-probe-0.3.0/src/lib.rs:91
────────────────────────────────────────────────────────────────────────────────
stack backtrace:
   0: HardFaultTrampoline
      <exception entry>
   1: lib::inline::__udf
        at ./asm/inline.rs:181:5
   2: __udf
        at ./asm/lib.rs:51:17
   3: cortex_m::asm::udf
        at .cargo/registry/src/github.com-1ecc6299db9ec823/cortex-m-0.7.6/src/asm.rs:43:5
   4: rust_begin_unwind
        at .cargo/registry/src/github.com-1ecc6299db9ec823/panic-probe-0.3.0/src/lib.rs:72:9
   5: core::panicking::panic_fmt
        at rustc/1c7b36d4db582cb47513a6c7176baaec1c3346ab/library/core/src/panicking.rs:142:14
   6: core::panicking::panic
        at /rustc/1c7b36d4db582cb47513a6c7176baaec1c3346ab/library/core/src/panicking.rs:48:5
   7: cyw43::Runner<PWR,SPI>::update_credit
        at /embassy/cyw43/src/lib.rs:919:16
   8: cyw43::Runner<PWR,SPI>::rx
        at /embassy/cyw43/src/lib.rs:808:9
   9: cyw43::Runner<PWR,SPI>::run::{{closure}}
        at /embassy/cyw43/src/lib.rs:727:21
  10: <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll
        at /rustc/1c7b36d4db582cb47513a6c7176baaec1c3346ab/library/core/src/future/mod.rs:91:19
  11: cyw43_example_rpi_pico_w::__wifi_task_task::{{closure}}
        at src/main.rs:32:17
---
 src/lib.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/lib.rs b/src/lib.rs
index 21b8b2d8..d9a21f4b 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -916,7 +916,7 @@ where
     fn update_credit(&mut self, sdpcm_header: &SdpcmHeader) {
         if sdpcm_header.channel_and_flags & 0xf < 3 {
             let mut sdpcm_seq_max = sdpcm_header.bus_data_credit;
-            if sdpcm_seq_max - self.sdpcm_seq > 0x40 {
+            if sdpcm_seq_max.wrapping_sub(self.sdpcm_seq) > 0x40 {
                 sdpcm_seq_max = self.sdpcm_seq + 2;
             }
             self.sdpcm_seq_max = sdpcm_seq_max;