fix for flash boot (ROM changes defaults)

examples/nxp/rt1060-evk-make-baremetal-builtin/sysinit.c

@@ -10,14 +10,18 @@
 uint32_t SystemCoreClock = SYS_FREQUENCY;
 
 // - 14.4, Figure 14-2: clock tree
-// - 14.7.4: ARM_PODF defaults to /2
+// - 14.7.4: ARM_PODF defaults to /2; 9.5.3 Table 9-7: ROM agrees
 // - 14.7.5: AHB_PODF defaults to /1; IPG_PODF defaults to /4; PERIPH_CLK_SEL
 // defaults to derive clock from pre_periph_clk_sel
-// - 14.7.6: PRE_PERIPH_CLK_SEL defaults to derive clock from divided PLL1.
-// - (For 528MHz operation, we need to set it to derive clock from PLL2).
+//   - 9.5.3 Table 9-7: ROM changes IPG_PODF to /3
+// - 14.7.6: PRE_PERIPH_CLK_SEL defaults to derive clock from divided
+// PLL1; 9.5.3 Table 9-7: ROM agrees
+// - (For 528MHz operation, we need to set it to derive clock from PLL2)
+// - 14.7.7: PER_CLK defaults to IPG/1; 9.5.3 Table 9-7: ROM changes it to IPG/2
 // - 14.6.1.3.1 ARM PLL (PLL1); 13.3.2.2 PLLs
 // - 14.8.1: PLL1 is powered off and bypassed to 24MHz. Fout = 24MHz *
 // div_select/2
+//   - 9.5.3 Table 9-7: ROM enables this PLL and sets it up
 // - For 600MHz operation, we need to set PLL1 on
 // - Datasheet 4.1.3: System frequency/Bus frequency max 600/150MHz respectively
 // (AHB/IPG)
@@ -42,9 +46,15 @@ void SystemInit(void) {  // Called automatically by startup code (ints masked)
   SETBITS(DCDC->REG3, DCDC_REG3_TRG_MASK, DCDC_REG3_TRG(0x12));
   while ((DCDC->REG0 & DCDC_REG0_STS_DC_OK_MASK) == 0)
     spin(1);  // Wait for DCDC_STS_DC_OK
+  // ROM fiddles with AHB divider, wait and then keep bits at 0 (expected)
+  while (CCM->CDHIPR & CCM_CDHIPR_AHB_PODF_BUSY_MASK) spin(1);
+  SETBITS(CCM->CBCDR, CCM_CBCDR_IPG_PODF_MASK | CCM_CBCDR_AHB_PODF_MASK,
+          CCM_CBCDR_IPG_PODF(3)); // keep AHB, set IPG divider /4 (150MHz)
   SETBITS(CCM->CSCMR1, CCM_CSCMR1_PERCLK_PODF_MASK,
           CCM_CSCMR1_PERCLK_PODF(1));  // Set PERCLK divider /2 (75MHz)
-  // Set clock to 600 MHz. Power PLL on and configure divider
+  // Set clock to 600 MHz. Power PLL on and configure divider (ROM boot code
+  // fiddles with the PLL, bypass first)
+  CCM_ANALOG->PLL_ARM |= CCM_ANALOG_PLL_ARM_BYPASS_MASK;
   SETBITS(CCM_ANALOG->PLL_ARM,
           CCM_ANALOG_PLL_ARM_POWERDOWN_MASK |
               CCM_ANALOG_PLL_ARM_SET_DIV_SELECT_MASK,
@@ -61,7 +71,8 @@ void SystemInit(void) {  // Called automatically by startup code (ints masked)
     spin(1);  // wait until it is stable
   CCM_ANALOG->PLL_USB1 &=
       ~CCM_ANALOG_PLL_USB1_BYPASS_MASK;  // Disable Bypass (switch to PLL)
-  CCM->CSCDR1 &= ~(CCM_CSCDR1_UART_CLK_SEL_MASK | CCM_CSCDR1_UART_CLK_PODF_MASK);
+  CCM->CSCDR1 &=
+      ~(CCM_CSCDR1_UART_CLK_SEL_MASK | CCM_CSCDR1_UART_CLK_PODF_MASK);
   rng_init();  // Initialise random number generator
   // NXP startup code calls SystemInit BEFORE initializing RAM...
   SysTick_Config(SYS_FREQUENCY / 1000);  // Sys tick every 1ms