3737use cast:: u32;
3838use cortex_m:: peripheral:: syst:: SystClkSource ;
3939use cortex_m:: peripheral:: SYST ;
40-
41- use crate :: nb:: block;
42- use crate :: rcc:: CoreClocks ;
43- use crate :: time:: { Hertz , U32Ext } ;
4440use embedded_hal:: {
4541 blocking:: delay:: { DelayMs , DelayUs } ,
4642 timer:: CountDown ,
4743} ;
44+ use void:: Void ;
45+
46+ use crate :: nb:: block;
47+ use crate :: rcc:: CoreClocks ;
48+ use crate :: time:: { Hertz , U32Ext } ;
4849
4950pub trait DelayExt {
5051 fn delay ( self , clocks : CoreClocks ) -> Delay ;
@@ -62,6 +63,88 @@ pub struct Delay {
6263 syst : SYST ,
6364}
6465
66+ /// Implements [CountDown](embedded_hal::timer::CountDown) for the System timer (SysTick).
67+ pub struct Countdown < ' a > {
68+ clocks : CoreClocks ,
69+ syst : & ' a mut SYST ,
70+ total_rvr : u64 ,
71+ finished : bool ,
72+ }
73+
74+ impl < ' a > Countdown < ' a > {
75+ /// Create a new [CountDown] measured in microseconds.
76+ pub fn new ( syst : & ' a mut SYST , clocks : CoreClocks ) -> Self {
77+ Self {
78+ syst,
79+ clocks,
80+ total_rvr : 0 ,
81+ finished : true ,
82+ }
83+ }
84+
85+ /// start a wait cycle and sets finished to true if [CountdownUs] is done waiting.
86+ fn start_wait ( & mut self ) {
87+ // The SysTick Reload Value register supports values between 1 and 0x00FFFFFF.
88+ const MAX_RVR : u32 = 0x00FF_FFFF ;
89+
90+ if self . total_rvr != 0 {
91+ self . finished = false ;
92+ let current_rvr = if self . total_rvr <= MAX_RVR . into ( ) {
93+ self . total_rvr as u32
94+ } else {
95+ MAX_RVR
96+ } ;
97+
98+ self . syst . set_reload ( current_rvr) ;
99+ self . syst . clear_current ( ) ;
100+ self . syst . enable_counter ( ) ;
101+
102+ self . total_rvr -= current_rvr as u64 ;
103+ } else {
104+ self . finished = true ;
105+ }
106+ }
107+ }
108+
109+ impl < ' a > CountDown for Countdown < ' a > {
110+ type Time = fugit:: MicrosDurationU32 ;
111+
112+ fn start < T > ( & mut self , count : T )
113+ where
114+ T : Into < Self :: Time > ,
115+ {
116+ let us = count. into ( ) . ticks ( ) ;
117+
118+ // With c_ck up to 480e6, we need u64 for delays > 8.9s
119+
120+ self . total_rvr = if cfg ! ( not( feature = "revision_v" ) ) {
121+ // See errata ES0392 §2.2.3. Revision Y does not have the /8 divider
122+ u64:: from ( us) * u64:: from ( self . clocks . c_ck ( ) . 0 / 1_000_000 )
123+ } else if cfg ! ( feature = "cm4" ) {
124+ // CM4 dervived from HCLK
125+ u64:: from ( us) * u64:: from ( self . clocks . hclk ( ) . 0 / 8_000_000 )
126+ } else {
127+ // Normally divide by 8
128+ u64:: from ( us) * u64:: from ( self . clocks . c_ck ( ) . 0 / 8_000_000 )
129+ } ;
130+
131+ self . start_wait ( ) ;
132+ }
133+
134+ fn wait ( & mut self ) -> nb:: Result < ( ) , Void > {
135+ if self . finished {
136+ return Ok ( ( ) ) ;
137+ }
138+
139+ if self . syst . has_wrapped ( ) {
140+ self . syst . disable_counter ( ) ;
141+ self . start_wait ( ) ;
142+ }
143+
144+ Err ( nb:: Error :: WouldBlock )
145+ }
146+ }
147+
65148impl Delay {
66149 /// Configures the system timer (SysTick) as a delay provider
67150pub fn new ( mut syst : SYST , clocks : CoreClocks ) -> Self {
@@ -105,7 +188,7 @@ impl DelayUs<u32> for Delay {
105188 // See errata ES0392 §2.2.3. Revision Y does not have the /8 divider
106189 u64:: from ( us) * u64:: from ( self . clocks . c_ck ( ) . 0 / 1_000_000 )
107190 } else if cfg ! ( feature = "cm4" ) {
108- // CM4 dervived from HCLK
191+ // CM4 derived from HCLK
109192 u64:: from ( us) * u64:: from ( self . clocks . hclk ( ) . 0 / 8_000_000 )
110193 } else {
111194 // Normally divide by 8
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