UNI/O Library for STM32F103

• Author: Tom LeMense
• Toolchain: Keil uVision/MDK
• Target: STM32F103TB (CM3, 128K Flash, 20K RAM)
• Hardware: STM32F103 Blue Pull
• Repository: github.com/tomcircuit/STM32F103_UNIO

Description

The main (only?) purpose for this is to allow usage of the Microchip 11AAxxx family of UNI/O EEPROM devices with an STM32F103 device. This code is largely based upon that of NESFreak MSP430_UNIO. I was able to adapt towards the STM32F103 with only a very few changes. Here, briefly, are the key differences from the MSP430 version:

• I chose to configure the UNI/O bus GPIO as Open Drain. This allows the pin to be read/written without having to change pin direction.

• The MSP430 driver used software timed loops for bit timing. I chose to use TIM3, one of the STM32F103's General Purpose Timers in a polled fashion. I did not bother to disable interrupts because the STM32F103 is normally running quite a bit faster than the bit timing, so any well-behaved ISR should not affect the timing very much. YMMV.

• There is a fair amount of overhead in the bit functions. The target bit timing is 32us per bit, but in my testing this was closer to 36us/bit with a 24MHz sysclk. Because the 11AAxxx EEPROM bit timing accuracy is non-critical, I did not really work too hard to optimize this. From my observations, the timing stability is sufficient.

• I changed many of the the function names, in an effort to make it more apparent what they do. For example, the functions that transmit to the UNI/O device have "send" in the name, and the functions that receive from the device have "receive" in the name. I followed suit for the "send_byte" and "send_n_bytes" functions, again for clarity. The words "read" and "write" are reserved for the EEPROM high level operations with the same names. I did not rename the hgher-level level EEPROM access functions, to ease porting.

• I exposed the SETAL and ERAL commands to allow bulk set and builk erase of the EEPROM bits. These require a separate UNIO_enable_write() call immediately beforehand.

Usage

UNIO.h has hardware-specific defines in it that will need to be reviewed and perhaps changed prior to use.

/* macros for UNIO pin maniuplation - here, B0 is assumed */
/* assumes that GPIO is configured as Open Drain output */
#define UNIO_LOW  do { GPIOB->BRR = GPIO_Pin_0; } while (0)
#define UNIO_HIGH do { GPIOB->BSRR = GPIO_Pin_0; } while (0)
#define UNIO_INP (GPIOB->IDR & GPIO_IDR_IDR0)

/* macros for GPT maninpultion - here TIM3 is assumed */
/* assumes that GPT is set for 1us/tick and One Pulse Mode */
#define GPT_START do { TIM3->CR1 |= TIM_CR1_CEN; } while (0)
#define GPT_STOP  do { TIM3->CR1 &= ~(TIM_CR1_CEN); } while (0)
#define GPT_RELOAD(val) do { TIM3->ARR = (val); } while (0)
#define GPT_UPDATE do { TIM3->EGR |= TIM_EGR_UG ; } while (0)
#define GPT_RUNNING (TIM3->CR1 & TIM_CR1_CEN)
#define GPT_DELAY do { __NOP(); } while (GPT_RUNNING)

The UNI/O bus frequency is also configured in UNIO.h

/* UNIO bus timing - all derived from UNIO_BIT_US */
/* !!THIS TIMING IS NOT ACCURATE! ADJUST IF BITRATE IS CRITICAL!! */
#define UNIO_BIT_US (32u)
#define UNIO_HALF_BIT_US ((UNIO_BIT_US / 2u) - 1u)
#define UNIO_QUARTER_BIT_US ((UNIO_BIT_US / 4u) - 1u)

Prior to using any of the UNIO functions, the STM32F103 GPIO and GPT peripherals must be enabled and configured. The main.c file in this repro gives an example of this, using B0 and TIM3. The underpininngs of this main.c file are the ST Standard Peripheral Library.

Tested under Keil MDK using STM32F103 "Blue Pill" board and a 11AA080 EEPROM device.

Tom LeMense, March 2024