MAX17851 no-OS driver
Supported Devices
Overview
The MAX17851 SPI to UART safety monitoring bridge translates communication from SPI format to universal asynchronous receiver transmitter (UART) format specially designed to interface with Maxim's Battery Management Data Acquisition System.
The safety monitoring bridge enables robust communication with baud rates extending up to 4Mbps in both single and dual daisy-chain system architectures. High throughput, dual UART systems can read 96 cells of battery voltages within 1173us.
THIS Uart Device is meant to be used alongside devices using Maxim's Battery Management System UART Protocol!
Applications
Battery Management Systems (BMS)
Electric and Hybrid Electric Vehicles (EV/HEV)
Energy Storage Systems (ESS)
Maxim Battery Management System UART Protocol
A message is defined as a sequence of UART characters. The message starts with a preamble character, followed by data characters, and ending with a stop character.
Each character consists of the following 12 bits: * One START bit * Eight data bits (LSB first) * One parity bit (even) * Two STOP bits
More than this, every data byte is transmitted and received as two separate characters (separated from one byte to two bytes), since every nibble is Manchester Encoded. Therefore each nibble becomes a byte (the bit number doubles), so a data byte splits into two characters.
Driver Initialization
In order to be able to use the device, you will have to provide the support for the communication protocol (SPI).
The first API to be called is max17851_init. Make sure that it returns 0, which means that the driver was initialized correctly.
Usually, this function is to be called from no_os_uart_init function, since max17851 can also be seen as a UART peripheral inside no-OS infrastructure.
For more details regarding UART API, please see No-OS UART API.
General Configuration
Baud Rate, Single/Dual UART and Operation Mode are properties that should be set at the initialization of the device, therefore they are found in the max17851_init function, although other configurations can be found there such as the : * Alert Debounce (max17851_set_alert_debounce). * GPIO Recovery Delay (max17851_reg_write to CONFIG_SAFEMON0 Register). * Contact Timer Delay (max17851_reg_write to CONFIG_SAFEMON1 Register). * Communication Timeout Retry Count (max17851_set_comm). * Safemon Delay (max17851_set_safemon_dly).
But more than this, the MAX17851 no-OS driver also provides access to UART related general configuration, that can be performed at run-time, such as : * MAX17851_TX_NOPREAMBLE_SEL - Transmits Message with no Preamble Byte. * MAX17851_TX_NOSTOP_SEL - Disables Stop Character from UART TX packages. * MAX17851_TX_PAUSE_SEL - Puts TX in idle state. * MAX17851_TX_ODDPARITY_SEL - Selects ODD parity for UART bits instead of EVEN. * MAX17851_TX_QUEUE_SEL - Enables transmission of the message from the queue. * MAX17851_TX_PREAMBLES_SEL - Transmits preambles continuously. * MAX17851_TX_RAW_DATA_SEL - Disables Manchester encoding from transmitted data. * MAX17851_RX_RAW_DATA_SEL - Disables Manchester encoding from received data.
Alert Packet Configuration
MAX17851 also comes with the Alert Packet feature, therefore ALERT pins can be initialized from the Slave BMS chip used alongside MAX17851 and receive an alert packet. MAX17851 gives the chance to monitor the specific alerts or enable/disable them, so an interrupt inside the MCU host unit can be performed in case of failures.
max17851_set_alrtpckt_time Sets the time for generating Alert Packets or sending keep-alive (stop) characters throughout UART.
max17851_set_alert and max17851_get_alert enable/disable specific alerts, respectively checks if a specific alert is triggered.
Read/Writing Messages Configuration
In order to send/receive UART messages using the MAX17851, a specific routine has to be performed for each operation.
Transmitting Messages:
For transmitting messages there are 4 queues, each one of them consisting of 32 bytes, first byte being the length of the message, rest of them being the data bytes need to be sent over UART (can or cannot be encoded, default settings require them not to be encoded, since the IC is taking care of the Mancheste Encoding).
Therefore the user can select wich queue is to be loaded (written to inside the IC memory) and which one to be sent over UART using the max17851_select_queue, each one being able to be seleted as the transmitt/load queue in case of manual message sending.
max17851_write_msg handles the whole transmitting of the message, using the first queue, therefore in this case the message can not be grater than 31 bytes.
Receving Messages:
max17851_read_msg is the API to be used in order to read the received buffer over UART.
For both transmitting and receiving messages, the read/write message API's handle the buffer clearance after the buffers are properly written/read.
Register Access
In case the user wants to use even more specific functionalities of the MAX17851 such as using the Continuously Preambles mode, or no STOP characters mode, etc. in order for a Hardware-In-The-Loop test or such, register access is provided as well as the whole register map being defined in the header file.
max17851_reg_write - Is to be used for register writing. max17851_reg_read - Is to be used for register reading.
No-OS platform operations
Since the MAX17851 is to be used as a UART peripheral in order to communicate with other BMS chips, it can be used as such inside the No-OS infrastructure and having specific platform ops, therefore a no-OS uart descriptor can be used and parsed for initialization in other BMS device drivers.
max17851_uart_init - Initializes the UART descriptor. max17851_uart_read - Reads data over the UART. max17851_uart_write - Writes data over the UART. max17851_uart_get_errors - Gets errors from the Alert Loop. max17851_uart_remove - Removes the UART descriptor.
MAX17851 Driver Initialization Example
struct max17851_desc *max17851_desc;
struct no_os_spi_init_param max17851_spi_ip = {
.device_id = 4,
.extra = &max17851_spi_extra,
.mode = NO_OS_SPI_MODE_0,
.max_speed_hz = 100000,
.platform_ops = &max_spi_ops,
.chip_select = 0,
};
struct max17851_init_param max17851_ip = {
.spi_param = &max17851_spi_ip,
.gpio1_param = NULL,
.gpio2_param = NULL,
.op_mode = MAX17851_MASTER_DUAL_UART,
.baud_rate = MAX17851_UART_BAUD_500K,
.no_dev = 1,
.single = false,
.contact_tmr_dly_4xmin = MAX17851_CONTACT_TIMER_DELAY_INFINITE,
.gpio_rec_dly_csec = MAX17851_GPIO_RECOVERY_DELAY_DISABLED,
.safemon_dly = MAX17851_SAFEMON_DLY_500MS,
};
ret = max17851_init(&max17851_desc, &max17851_ip);
if (ret)
return ret;
MAX17851 UART Descriptor Initialization Example
struct no_os_uart_desc *uart_desc;
struct max_spi_init_param max17851_spi_extra = {
.num_slaves = 1,
.polarity = SPI_SS_POL_LOW,
.vssel = MXC_GPIO_VSSEL_VDDIOH
};
struct no_os_spi_init_param max17851_spi_ip = {
.device_id = 4,
.extra = &max17851_spi_extra,
.mode = NO_OS_SPI_MODE_0,
.max_speed_hz = 100000,
.platform_ops = &max_spi_ops,
.chip_select = 0,
};
struct max17851_init_param uart_extra = {
.spi_param = &max17851_spi_ip,
.gpio1_param = NULL,
.gpio2_param = NULL,
.op_mode = MAX17851_MASTER_DUAL_UART,
.baud_rate = MAX17851_UART_BAUD_500K,
.no_dev = 1,
.single = false,
.contact_tmr_dly_4xmin = MAX17851_CONTACT_TIMER_DELAY_INFINITE,
.gpio_rec_dly_csec = MAX17851_GPIO_RECOVERY_DELAY_DISABLED,
.safemon_dly = MAX17851_SAFEMON_DLY_500MS,
};
struct no_os_uart_init_param uart_ip = {
.device_id = 0,
.irq_id = NULL,
.baud_rate = 500000,
.size = NO_OS_UART_CS_8,
.platform_ops = &max17851_uart_ops,
.parity = NO_OS_UART_PAR_EVEN,
.stop = NO_OS_UART_STOP_2_BIT,
.extra = &uart_extra,
};
ret = no_os_uart_init(&uart_desc, &uart_ip);
if (ret)
return ret;