Merge #328

328: Prevent underflow when calling delay(n) with n<2 r=jonas-schievink a=ovidiusabou

Calling delay(1) causes a very long wait (freeze) otherwise.
86cd463788b97ca3894936101c6cf4f3512f0fbc introduced this behaviour by
changing the cycle count from n / 4 + 1 to n / 2 which forces an
underflow when n<2.

Co-authored-by: Ovidiu Sabou <ovidiu@sabou.org>
Co-authored-by: Jonas Schievink <jonasschievink@gmail.com>

15 files changed, 2 insertions, 1 deletions

diff --git a/asm/inline.rs b/asm/inline.rs
index ef203cd..5887baf 100644
--- a/asm/inline.rs
+++ b/asm/inline.rs
@@ -55,7 +55,8 @@ pub unsafe fn __delay(cyc: u32) {
     // The loop will normally take 3 to 4 CPU cycles per iteration, but superscalar cores
     // (eg. Cortex-M7) can potentially do it in 2, so we use that as the lower bound, since delaying
     // for more cycles is okay.
-    let real_cyc = cyc / 2;
+    // Add 1 to prevent an integer underflow which would cause a long freeze
+    let real_cyc = 1 + cyc / 2;
     asm!(
         // Use local labels to avoid R_ARM_THM_JUMP8 relocations which fail on thumbv6m.
         "1:",
diff --git a/bin/thumbv6m-none-eabi-lto.a b/bin/thumbv6m-none-eabi-lto.a
index 6506bd8..6136ec6 100644
--- a/bin/thumbv6m-none-eabi-lto.a
+++ b/bin/thumbv6m-none-eabi-lto.a
diff --git a/bin/thumbv6m-none-eabi.a b/bin/thumbv6m-none-eabi.a
index 48fe997..c42f579 100644
--- a/bin/thumbv6m-none-eabi.a
+++ b/bin/thumbv6m-none-eabi.a
diff --git a/bin/thumbv7em-none-eabi-lto.a b/bin/thumbv7em-none-eabi-lto.a
index ce6bd4c..c2c040a 100644
--- a/bin/thumbv7em-none-eabi-lto.a
+++ b/bin/thumbv7em-none-eabi-lto.a
diff --git a/bin/thumbv7em-none-eabi.a b/bin/thumbv7em-none-eabi.a
index 637a884..660360f 100644
--- a/bin/thumbv7em-none-eabi.a
+++ b/bin/thumbv7em-none-eabi.a
diff --git a/bin/thumbv7em-none-eabihf-lto.a b/bin/thumbv7em-none-eabihf-lto.a
index 6f7edb3..eba1984 100644
--- a/bin/thumbv7em-none-eabihf-lto.a
+++ b/bin/thumbv7em-none-eabihf-lto.a
diff --git a/bin/thumbv7em-none-eabihf.a b/bin/thumbv7em-none-eabihf.a
index f25d0ef..1561fa4 100644
--- a/bin/thumbv7em-none-eabihf.a
+++ b/bin/thumbv7em-none-eabihf.a
diff --git a/bin/thumbv7m-none-eabi-lto.a b/bin/thumbv7m-none-eabi-lto.a
index 485219b..d964314 100644
--- a/bin/thumbv7m-none-eabi-lto.a
+++ b/bin/thumbv7m-none-eabi-lto.a
diff --git a/bin/thumbv7m-none-eabi.a b/bin/thumbv7m-none-eabi.a
index d3a1213..f541274 100644
--- a/bin/thumbv7m-none-eabi.a
+++ b/bin/thumbv7m-none-eabi.a
diff --git a/bin/thumbv8m.base-none-eabi-lto.a b/bin/thumbv8m.base-none-eabi-lto.a
index bd79b05..8a6ed42 100644
--- a/bin/thumbv8m.base-none-eabi-lto.a
+++ b/bin/thumbv8m.base-none-eabi-lto.a
diff --git a/bin/thumbv8m.base-none-eabi.a b/bin/thumbv8m.base-none-eabi.a
index 130e413..33cd908 100644
--- a/bin/thumbv8m.base-none-eabi.a
+++ b/bin/thumbv8m.base-none-eabi.a
diff --git a/bin/thumbv8m.main-none-eabi-lto.a b/bin/thumbv8m.main-none-eabi-lto.a
index 4be0c0d..8e6ff0a 100644
--- a/bin/thumbv8m.main-none-eabi-lto.a
+++ b/bin/thumbv8m.main-none-eabi-lto.a
diff --git a/bin/thumbv8m.main-none-eabi.a b/bin/thumbv8m.main-none-eabi.a
index 74a5786..898fea7 100644
--- a/bin/thumbv8m.main-none-eabi.a
+++ b/bin/thumbv8m.main-none-eabi.a
diff --git a/bin/thumbv8m.main-none-eabihf-lto.a b/bin/thumbv8m.main-none-eabihf-lto.a
index 2920ea4..d9a636a 100644
--- a/bin/thumbv8m.main-none-eabihf-lto.a
+++ b/bin/thumbv8m.main-none-eabihf-lto.a
diff --git a/bin/thumbv8m.main-none-eabihf.a b/bin/thumbv8m.main-none-eabihf.a
index b547b0f..b0513b7 100644
--- a/bin/thumbv8m.main-none-eabihf.a
+++ b/bin/thumbv8m.main-none-eabihf.a