altos: Use SYSTICK on STM32L

It's probably more power efficient than using one of the timers, and
it's certainly easier to configure.

Signed-off-by: Keith Packard <keithp@keithp.com>

4 files changed, 30 insertions, 31 deletions

diff --git a/src/stm/ao_arch.h b/src/stm/ao_arch.h
index 007f7e2e..27a942f2 100644
--- a/src/stm/ao_arch.h
+++ b/src/stm/ao_arch.h
@@ -99,6 +99,7 @@ extern const uint32_t ao_radio_cal;
 #define AO_HCLK		(AO_SYSCLK / AO_AHB_PRESCALER)
 #define AO_PCLK1	(AO_HCLK / AO_APB1_PRESCALER)
 #define AO_PCLK2	(AO_HCLK / AO_APB2_PRESCALER)
+#define AO_SYSTICK	(AO_HCLK / 8)
 
 #if AO_APB1_PRESCALER == 1
 #define AO_TIM23467_CLK		AO_PCLK1
diff --git a/src/stm/ao_timer.c b/src/stm/ao_timer.c
index 8b7c2327..5976eb3f 100644
--- a/src/stm/ao_timer.c
+++ b/src/stm/ao_timer.c
@@ -31,14 +31,9 @@ volatile __data uint8_t	ao_data_interval = 1;
 volatile __data uint8_t	ao_data_count;
 #endif
 
-void
-ao_debug_out(char c);
-
-
-void stm_tim6_isr(void)
+void stm_systick_isr(void)
 {
-	if (stm_tim6.sr & (1 << STM_TIM67_SR_UIF)) {
-		stm_tim6.sr = 0;
+	if (stm_systick.csr & (1 << STM_SYSTICK_CSR_COUNTFLAG)) {
 		++ao_tick_count;
 #if HAS_TASK_QUEUE
 		if (ao_task_alarm_tick && (int16_t) (ao_tick_count - ao_task_alarm_tick) >= 0)
@@ -81,33 +76,16 @@ ao_timer_set_adc_interval(uint8_t interval)
 
 #define TIMER_10kHz	((AO_PCLK1 * TIMER_23467_SCALER) / 10000)
 
+#define SYSTICK_RELOAD (AO_SYSTICK / 100 - 1)
+
 void
 ao_timer_init(void)
 {
-	stm_nvic_set_enable(STM_ISR_TIM6_POS);
-	stm_nvic_set_priority(STM_ISR_TIM6_POS, AO_STM_NVIC_CLOCK_PRIORITY);
-
-	/* Turn on timer 6 */
-	stm_rcc.apb1enr |= (1 << STM_RCC_APB1ENR_TIM6EN);
-
-	stm_tim6.psc = TIMER_10kHz;
-	stm_tim6.arr = 99;
-	stm_tim6.cnt = 0;
-
-	/* Enable update interrupt */
-	stm_tim6.dier = (1 << STM_TIM67_DIER_UIE);
-
-	/* Poke timer to reload values */
-	stm_tim6.egr |= (1 << STM_TIM67_EGR_UG);
-
-	stm_tim6.cr2 = (STM_TIM67_CR2_MMS_RESET << STM_TIM67_CR2_MMS);
-
-	/* And turn it on */
-	stm_tim6.cr1 = ((0 << STM_TIM67_CR1_ARPE) |
-			(0 << STM_TIM67_CR1_OPM) |
-			(1 << STM_TIM67_CR1_URS) |
-			(0 << STM_TIM67_CR1_UDIS) |
-			(1 << STM_TIM67_CR1_CEN));
+	stm_systick.rvr = SYSTICK_RELOAD;
+	stm_systick.cvr = 0;
+	stm_systick.csr = ((1 << STM_SYSTICK_CSR_ENABLE) |
+			   (1 << STM_SYSTICK_CSR_TICKINT) |
+			   (STM_SYSTICK_CSR_CLKSOURCE_HCLK_8 << STM_SYSTICK_CSR_CLKSOURCE));
 }
 
 void
diff --git a/src/stm/registers.ld b/src/stm/registers.ld
index 95a86e35..8318c75a 100644
--- a/src/stm/registers.ld
+++ b/src/stm/registers.ld
@@ -44,6 +44,8 @@ stm_tim4   = 0x40000800;
 stm_tim3   = 0x40000400;
 stm_tim2   = 0x40000000;
 
+stm_systick = 0xe000e010;
+
 stm_nvic   = 0xe000e100;
 
 stm_scb    = 0xe000ed00;
diff --git a/src/stm/stm32l.h b/src/stm/stm32l.h
index 1d636037..5c0748a6 100644
--- a/src/stm/stm32l.h
+++ b/src/stm/stm32l.h
@@ -811,6 +811,24 @@ extern struct stm_lcd stm_lcd;
 #define STM_LCD_CLR_UDDC		(3)
 #define STM_LCD_CLR_SOFC		(1)
 
+/* The SYSTICK starts at 0xe000e010 */
+
+struct stm_systick {
+	vuint32_t	csr;
+	vuint32_t	rvr;
+	vuint32_t	cvr;
+	vuint32_t	calib;
+};
+
+extern struct stm_systick stm_systick;
+
+#define STM_SYSTICK_CSR_ENABLE		0
+#define STM_SYSTICK_CSR_TICKINT		1
+#define STM_SYSTICK_CSR_CLKSOURCE	2
+#define  STM_SYSTICK_CSR_CLKSOURCE_HCLK_8		0
+#define  STM_SYSTICK_CSR_CLKSOURCE_HCLK			1
+#define STM_SYSTICK_CSR_COUNTFLAG	16
+
 /* The NVIC starts at 0xe000e100, so add that to the offsets to find the absolute address */
 
 struct stm_nvic {