Make more ringbufs zero-initialized, saving flash

To simplify its implementation, ringbuf currently requires every ringbuf
to be declared with an initialization element. It creates a static array
containing that element.

If that element is represented as zero, that goes in BSS and is
zero-initialized with the rest of BSS.

If that element is represented as anything other than zero, the compiler
creates a full-sized "initialization image" copy of the ringbuf _in
flash_ that it can then memcpy into RAM on startup.

Using the default Rust enum representation, the easiest way to get a
ringbuf initialized to non-zero bytes is to put its initialization
sentinel value (e.g. None) as the last variant in the enum.
Unfortunately, this is super common.

This commit moves all the ones I could find, which should reduce flash
usage in a bunch of cases.

Author: cbiffle

app/cosmo/src/tracing.rs

@@ -27,8 +27,8 @@ enum Event {
 
 #[derive(Copy, Clone, PartialEq)]
 enum Trace {
-    Event(Event),
     None,
+    Event(Event),
 }
 
 ringbuf!(Trace, 128, Trace::None);

app/gimlet/src/tracing.rs

@@ -27,8 +27,8 @@ enum Event {
 
 #[derive(Copy, Clone, PartialEq)]
 enum Trace {
-    Event(Event),
     None,
+    Event(Event),
 }
 
 ringbuf!(Trace, 128, Trace::None);

drv/cosmo-seq-server/src/main.rs

@@ -38,6 +38,8 @@ task_slot!(PACKRAT, packrat);
 
 #[derive(Copy, Clone, PartialEq, Count)]
 enum Trace {
+    #[count(skip)]
+    None,
     FpgaInit,
     StartFailed(#[count(children)] SeqError),
     ContinueBitstreamLoad(usize),
@@ -78,8 +80,6 @@ enum Trace {
         sp5r3: bool,
         sp5r4: bool,
     },
-    #[count(skip)]
-    None,
 }
 counted_ringbuf!(Trace, 128, Trace::None);
 

drv/gimlet-seq-server/src/main.rs

@@ -67,6 +67,8 @@ enum I2cTxn {
 
 #[derive(Copy, Clone, PartialEq, Count)]
 enum Trace {
+    #[count(skip)]
+    None,
     Ice40Rails(bool, bool),
     IdentValid(#[count(children)] bool),
     ChecksumValid(#[count(children)] bool),
@@ -150,8 +152,6 @@ enum Trace {
         retries_remaining: u8,
     },
     StartFailed(#[count(children)] SeqError),
-    #[count(skip)]
-    None,
 }
 
 counted_ringbuf!(Trace, 128, Trace::None);

drv/gimlet-seq-server/src/vcore.rs

@@ -41,6 +41,7 @@ pub struct VCore {
 
 #[derive(Copy, Clone, PartialEq)]
 enum Trace {
+    None,
     Initializing,
     Initialized,
     LimitLoaded,
@@ -49,7 +50,6 @@ enum Trace {
     Fault,
     Reading { timestamp: u64, volts: units::Volts },
     Error(ResponseCode),
-    None,
 }
 
 ringbuf!(Trace, 120, Trace::None);

drv/grapefruit-seq-server/src/main.rs

@@ -22,11 +22,11 @@ task_slot!(LOADER, spartan7_loader);
 
 #[derive(Copy, Clone, PartialEq, Count)]
 enum Trace {
-    MacsAlreadySet(MacAddressBlock),
-    IdentityAlreadySet(VpdIdentity),
-
     #[count(skip)]
     None,
+
+    MacsAlreadySet(MacAddressBlock),
+    IdentityAlreadySet(VpdIdentity),
 }
 
 counted_ringbuf!(Trace, 128, Trace::None);

drv/i2c-devices/src/adm1272.rs

@@ -81,10 +81,10 @@ impl core::fmt::Display for Adm1272 {
 
 #[derive(Copy, Clone, PartialEq)]
 enum Trace {
+    None,
     Coefficients(pmbus::Coefficients),
     Config(adm1272::PMON_CONFIG::CommandData),
     WriteConfig(adm1272::PMON_CONFIG::CommandData),
-    None,
 }
 
 ringbuf!(Trace, 8, Trace::None);

drv/i2c-devices/src/ds2482.rs

@@ -67,11 +67,11 @@ pub enum Error {
 
 #[derive(Copy, Clone, PartialEq)]
 enum Trace {
+    None,
     Read(Register, u8),
     ReadError(Register, ResponseCode),
     Command(Command),
     CommandError(Command, ResponseCode),
-    None,
 }
 
 ringbuf!(Trace, 196, Trace::None);

drv/i2c-devices/src/emc2305.rs

@@ -216,10 +216,10 @@ fn write_reg16(
 
 #[derive(Copy, Clone, PartialEq)]
 enum Trace {
+    None,
     ZeroTach(Fan),
     TachOverflow(u32),
     BadFanCount(u8),
-    None,
 }
 
 ringbuf!(Trace, 6, Trace::None);

drv/i2c-devices/src/lm5066.rs

@@ -101,10 +101,10 @@ impl core::fmt::Display for Lm5066 {
 
 #[derive(Copy, Clone, PartialEq)]
 pub enum Trace {
+    None,
     CurrentCoefficients(pmbus::Coefficients),
     PowerCoefficients(pmbus::Coefficients),
     DeviceSetup(lm5066::DEVICE_SETUP::CommandData),
-    None,
 }
 
 ringbuf!(Trace, 8, Trace::None);