stm32: ADC timing rework and fixes in stm32h7_adc.c

The stm32l412 doesn't have a PLLSAI1 clock and therefore the CKMODE
should not be set to zero.

The stm32h7 chips run the adc at 25mhz, so BOOST should be set to
0b10.

Improve timing comments.

Signed-off-by: Kevin O'Connor <[email protected]>

src/stm32/stm32h7_adc.c

@@ -12,21 +12,6 @@
 #include "internal.h" // GPIO
 #include "sched.h" // sched_shutdown
 
-#if CONFIG_MACH_STM32H7
-  #define ADC_CKMODE                          (0b11)
-  #define ADC_ATICKS                          (0b101)
-  #if CONFIG_MACH_STM32H723
-    #define PCSEL                               PCSEL_RES0
-  #endif
-#elif CONFIG_MACH_STM32L4
-  #define ADC_CKMODE                          (0)
-  #define ADC_ATICKS                          (0b100)
-#elif CONFIG_MACH_STM32G4
-  #define ADC_CKMODE                          (0b11)
-  #define ADC_ATICKS                          (0b100)
-  #define ADC_CCR_TSEN                        (ADC_CCR_VSENSESEL)
-#endif
-
 #define ADC_TEMPERATURE_PIN 0xfe
 DECL_ENUMERATION("pin", "ADC_TEMPERATURE", ADC_TEMPERATURE_PIN);
 
@@ -169,9 +154,20 @@ static const uint8_t adc_pins[] = {
 #endif
 };
 
+// ADC timing
+#define ADC_CKMODE 0b11
+#define ADC_ATICKS (CONFIG_MACH_STM32H7 ? 0b101 : 0b100)
+// stm32h7: clock=25Mhz, Tsamp=64.5, Tconv=71, total=2.84us
+// stm32h723 adc3: clock=50Mhz, Tsamp=92.5, Tconv=105, total=2.1us
+// stm32l4: clock=20Mhz, Tsamp=47.5, Tconv=60, total=3.0us
+// stm32g4: clock=37.5Mhz, Tsamp=47.5, Tconv=60, total=1.6us
 
-// ADC timing:
-// ADC clock=30Mhz, Tconv=6.5, Tsamp=64.5, total=2.3666us*OVERSAMPLES
+// Handle register name differences between chips
+#if CONFIG_MACH_STM32H723
+  #define PCSEL PCSEL_RES0
+#elif CONFIG_MACH_STM32G4
+  #define ADC_CCR_TSEN ADC_CCR_VSENSESEL
+#endif
 
 struct gpio_adc
 gpio_adc_setup(uint32_t pin)
@@ -185,9 +181,7 @@ gpio_adc_setup(uint32_t pin)
             break;
     }
 
-    // Determine which ADC block to use, enable peripheral clock
-    // (SYSCLK 480Mhz) /HPRE(2) /CKMODE divider(4) /additional divider(2)
-    // (ADC clock 30Mhz)
+    // Determine which ADC block to use and enable its clock
     ADC_TypeDef *adc;
     ADC_Common_TypeDef *adc_common;
 #ifdef ADC3
@@ -225,9 +219,9 @@ gpio_adc_setup(uint32_t pin)
         while (timer_is_before(timer_read_time(), end))
             ;
 
-        // Set Boost mode for 25Mhz < ADC clock <= 50Mhz
+        // Set boost mode on stm32h7 (adc clock is at 25Mhz)
 #ifdef ADC_CR_BOOST
-        MODIFY_REG(adc->CR, ADC_CR_BOOST_Msk, 0b11 << ADC_CR_BOOST_Pos);
+        MODIFY_REG(adc->CR, ADC_CR_BOOST_Msk, 0b10 << ADC_CR_BOOST_Pos);
 #endif
 
         // Calibration
@@ -250,19 +244,14 @@ gpio_adc_setup(uint32_t pin)
         while(!(adc->ISR & ADC_ISR_ADRDY))
            ;
 
-        // Set 64.5 ADC clock cycles sample time for every channel
-        // (Reference manual pg.940)
+        // Set ADC clock cycles sample time for every channel
         uint32_t aticks = ADC_ATICKS;
-        // Channel 0-9
-        adc->SMPR1 = (aticks        | (aticks << 3)  | (aticks << 6)
-                   | (aticks << 9)  | (aticks << 12) | (aticks << 15)
-                   | (aticks << 18) | (aticks << 21) | (aticks << 24)
-                   | (aticks << 27));
-        // Channel 10-19
-        adc->SMPR2 = (aticks        | (aticks << 3)  | (aticks << 6)
-                   | (aticks << 9)  | (aticks << 12) | (aticks << 15)
-                   | (aticks << 18) | (aticks << 21) | (aticks << 24)
-                   | (aticks << 27));
+        uint32_t av = (aticks           | (aticks << 3)  | (aticks << 6)
+                       | (aticks << 9)  | (aticks << 12) | (aticks << 15)
+                       | (aticks << 18) | (aticks << 21) | (aticks << 24)
+                       | (aticks << 27));
+        adc->SMPR1 = av;
+        adc->SMPR2 = av;
 
         // The stm32h7 chips need to be set to 12bit samples
 #if CONFIG_MACH_STM32H7