I am trying to set up ADC1 on STM32F103C6 "bare metal" (no HAL or LL). I've successfully done this on F0 series without difficulty, but this has me stumped. I've also referred to source code generated by STM32CubeMX (for just this device on this target) but it appears that is not succeeding.
Below is relevant code and some print statements generated by that code (the CPU is set for 24 MHz, ADC prescaler is divide-by-2, so ADC clock is at 12 MHz and proceeds from there):
// STM32F103C6
// CPU clock 24 MHz
// Initialize ADC1
// Single reading from mux 17 (Vrefint)
// ADC1 prescaler set to divide-by-2:
// RCC->CFGR ADCPRE[1:0] = 00: PCLK2 divided by 2
// ADC1 clock frequency = 12 MHz
Before initialization
ADC1 Base: 40012400
ADC1->CR1: 00000000
ADC1->CR2: 00000000
ADC1->SQR1: 00000000
ADC1->SQR2: 00000000
ADC1->SQR3: 00000000
// STM32F103: Initialize ADC1 for single software-initiated conversions
RCC->APB2ENR |= RCC_APB2ENR_ADC1EN; // Turn on ADC1 clock
for (uint16_t volatile i = 0; i < 1000; i++); // time delay --- wait for turn-on to complete
ADC1->CR2 |= ADC_CR2_TSVREFE; // Turn on temperature sensor, refint channels
ADC1->CR2 |= ADC_CR2_EXTSEL_2 | ADC_CR2_EXTSEL_1 | ADC_CR2_EXTSEL_0; // Regular group SWSTART only
ADC1->CR2 |= ADC_CR2_ADON; // Turn on ADC1
for (uint16_t volatile i = 0; i < 1000; i++); // time delay --- wait for turn-on to complete
ADC1->SQR1 = 0; // Single channel in regular group
ADC1->SQR2 = 0; // Single channel in regular group
ADC1->SQR3 = 0x11; // Single channel in regular group - Channel 0x11 - Vrefint
After initialization, before first conversion
ADC1 Base: 40012400
ADC1->CR1: 00000000
ADC1->CR2: 008E0001
ADC1->SQR1: 00000000
ADC1->SQR2: 00000000
ADC1->SQR3: 00000011
// STM32F103: Perform one conversion from channel 0x11 (Vrefint)
ADC1->CR2 |= ADC_CR2_SWSTART; // Start conversion
// Before ADC_CR2_SWSTART is set
ADC1->SR.EOC: 0
// After ADC_CR2_SWSTART is set
ADC1->SR.EOC: 0
// After time delay (EOC never appears)
ADC1->SR.EOC: 0
ADC1->DR: 00000000
