From 08df288985425390cf803b5384dac9fd102a86ab Mon Sep 17 00:00:00 2001
From: Karl Fessel <karl.fessel@ml-pa.com>
Date: Fri, 23 Jan 2026 15:54:49 +0100
Subject: [PATCH] cpu/samd5x: support for using ext_osc + xosc + fdpll

---
 cpu/samd5x/cpu.c | 54 +++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 46 insertions(+), 8 deletions(-)

diff --git a/cpu/samd5x/cpu.c b/cpu/samd5x/cpu.c
index 379471251f18..d30bbaca14af 100644
--- a/cpu/samd5x/cpu.c
+++ b/cpu/samd5x/cpu.c
@@ -74,7 +74,9 @@ the CPU frequency can't exceed it's frequency.
 /* Main clock > 48 MHz -> use DPLL, otherwise use DFLL */
 #  define USE_DPLL (CLOCK_CORECLOCK > SAM0_DFLL_FREQ_HZ)
 #  define USE_DFLL 1
+#ifndef USE_XOSC
 #  define USE_XOSC 0
+#endif
 
 #  ifndef GCLK_TIMER_HZ
 #    define GCLK_TIMER_HZ MHZ(8)
@@ -115,9 +117,18 @@ static void xosc32k_init(void)
     while (!(OSC32KCTRL->STATUS.reg & OSC32KCTRL_STATUS_XOSC32KRDY)) {}
 }
 
+#ifndef XOSC0_EXT_OSC
+#  define XOSC0_EXT_OSC (0)
+#endif
+
+#ifndef XOSC1_EXT_OSC
+#  define XOSC1_EXT_OSC (0)
+#endif
+
 static void xosc_init(uint8_t idx)
 {
     uint32_t freq;
+    bool xtal;
 
     if (!USE_XOSC ||
             (idx == 0 && XOSC0_FREQUENCY == 0) ||
@@ -130,9 +141,17 @@ static void xosc_init(uint8_t idx)
 
     if (idx == 0) {
         freq = XOSC0_FREQUENCY;
+        xtal = !XOSC0_EXT_OSC;
     }
     else if (idx == 1) {
         freq = XOSC1_FREQUENCY;
+        xtal = !XOSC1_EXT_OSC;
+    }
+
+    if (xtal) {
+        OSCCTRL->XOSCCTRL[idx].reg = OSCCTRL_XOSCCTRL_ENABLE;
+        while (!(OSCCTRL->STATUS.vec.XOSCRDY & (idx + 1))) {}
+        return;
     }
 
     uint32_t reg = OSCCTRL_XOSCCTRL_XTALEN
@@ -204,6 +223,10 @@ static void fdpll_init_nolock(uint8_t idx, uint32_t f_cpu, uint8_t flags)
     OSCCTRL->Dpll[idx].DPLLCTRLA.reg = 0;
     while (OSCCTRL->Dpll[idx].DPLLSYNCBUSY.reg) {}
 
+     /* holds LDR 13 bit integer and 5 bit fractional part:
+      * - integer part: ldr13_5 >> 5
+      * - fractional part: ldr13_5 & 0x1f */
+    uint32_t ldr13_5;
     uint32_t ctrlb = 0;
 
     /* HW revision before F  (A and D) might false unlock -> LBYPASS and WUF */
@@ -217,12 +240,25 @@ static void fdpll_init_nolock(uint8_t idx, uint32_t f_cpu, uint8_t flags)
      * (critical for some application not so much for other)*/
     if (EXTERNAL_OSC32_SOURCE) {
         /* Source the DPLL from 32kHz XOSC32 ( equivalent to ((f_cpu << 5) / 32768) ) */
-        const uint32_t LDR = (f_cpu >> 10);
-        OSCCTRL->Dpll[idx].DPLLRATIO.reg = OSCCTRL_DPLLRATIO_LDRFRAC(LDR & 0x1F)
-                                         | OSCCTRL_DPLLRATIO_LDR((LDR >> 5) - 1);
-
+        ldr13_5  = (f_cpu >> 10);
         ctrlb |= OSCCTRL_DPLLCTRLB_REFCLK_XOSC32;
-        OSCCTRL->Dpll[idx].DPLLCTRLB.reg = ctrlb;
+    }
+    else if (XOSC1_FREQUENCY) {
+        /* Source the DPLL from XOSC1 equivalent to ((f_cpu << 5) / 32768) ) */
+        /* fCLK_DPLLn = fCKR × (LDR + 1 + LDRFRAC/32)*/
+        /* fDIV = fXOSC / 2 * ( DIV + 1) */
+        /* divide to 1 MHz then multiply to fcpu  */
+        const uint32_t div = (XOSC1_FREQUENCY / MHZ(1) / 2) -1;
+        ldr13_5 = (f_cpu / MHZ(1)) << 5;
+        ctrlb |= OSCCTRL_DPLLCTRLB_DIV(DIV) | OSCCTRL_DPLLCTRLB_REFCLK_XOSC1;
+    }
+    else if (XOSC0_FREQUENCY) {
+        /* Source the DPLL from XOSC0 /* divide to 1 MHz then multiply to fcpu  */
+        /* fCLK_DPLLn = fCKR × (LDR + 1 + LDRFRAC/32)*/
+        /* fDIV = fXOSC / 2 * ( DIV + 1) */
+        const uint32_t div = (XOSC0_FREQUENCY / MHZ(1) / 2) -1;
+        ldr13_5 = (f_cpu / MHZ(1)) << 5;
+        ctrlb |= OSCCTRL_DPLLCTRLB_DIV(div) | OSCCTRL_DPLLCTRLB_REFCLK_XOSC0;
     }
     else {
         /* TODO find a better fallback source (eg 48MCLK routed though gclk divided down to 1MHz)
@@ -232,11 +268,13 @@ static void fdpll_init_nolock(uint8_t idx, uint32_t f_cpu, uint8_t flags)
         while (!(GCLK->PCHCTRL[OSCCTRL_GCLK_ID_FDPLL0 + idx].reg & GCLK_PCHCTRL_CHEN)) {}
         /* Source the DPLL from 32kHz GCLK1 ( equivalent to ((f_cpu << 5) / 32768) )
          * avoid the routing through gclk when XOSC32 is the source */
-        const uint32_t LDR = (f_cpu >> 10);
-        OSCCTRL->Dpll[idx].DPLLRATIO.reg  = OSCCTRL_DPLLRATIO_LDRFRAC(LDR & 0x1F)
-                                            | OSCCTRL_DPLLRATIO_LDR((LDR >> 5) - 1);
+        ldr13_5 = (f_cpu >> 10);
         ctrlb |= OSCCTRL_DPLLCTRLB_REFCLK_GCLK;
     }
+
+    OSCCTRL->Dpll[idx].DPLLRATIO.reg = OSCCTRL_DPLLRATIO_LDRFRAC(ldr13_5 & 0x1F)
+                                     | OSCCTRL_DPLLRATIO_LDR((ldr13_5 >> 5) - 1);
+
     OSCCTRL->Dpll[idx].DPLLCTRLB.reg = ctrlb;
     OSCCTRL->Dpll[idx].DPLLCTRLA.reg = OSCCTRL_DPLLCTRLA_ENABLE | flags;