我试图进行基本的握手。以下是C8051F120的SMBus（系统管理总线）的ISR。我试图在其上实现一个I2C设备（ads1115 7addr 0x48，对于那些好奇的人）。请注意，这主要是硅实验室为F120提供的示例。
void SMBUS_ISR (void) interrupt 7
{
bit FAIL = 0; // Used by the ISR to flag failed
// transfers
static unsigned char sent_byte_counter;
static unsigned char rec_byte_counter;
// Status code for the SMBus (SMB0STA register)
switch (SMB0STA)
{
// Master Transmitter/Receiver: START condition transmitted.
// Load SMB0DAT with slave device address.
case SMB_START: //0x08
// Master Transmitter/Receiver: repeated START condition transmitted.
// Load SMB0DAT with slave device address
case SMB_RP_START: //0x10
SMB0DAT = TARGET; // Load address of the slave.
SMB0DAT &= 0xFE; // Clear the LSB of the address for the
// R/W bit
SMB0DAT |= SMB_RW; // Load R/W bit
STA = 0; // Manually clear STA bit
rec_byte_counter = 1; // Reset the counter
sent_byte_counter = 1; // Reset the counter
break;
// Master Transmitter: Slave address + WRITE transmitted. ACK received.
// For a READ: N/A
//
// For a WRITE: Send the first data byte to the slave.
case SMB_MTADDACK: //0x18
SMB0DAT = SMB_DATA_OUT[sent_byte_counter-1];
sent_byte_counter++;
break;
// Master Transmitter: Slave address + WRITE transmitted. NACK received.
// Restart the transfer.
case SMB_MTADDNACK: //0x20
STA = 1; // Restart transfer
break;
// Master Transmitter: Data byte transmitted. ACK received.
// For a READ: N/A
//
// For a WRITE: Send all data. After the last data byte, send the stop
// bit.
case SMB_MTDBACK: //0x28
if (sent_byte_counter <= NUM_BYTES_WR)
{
// send data byte
SMB0DAT = SMB_DATA_OUT[sent_byte_counter-1];
sent_byte_counter++;
}
else
{
STO = 1; // Set STO to terminate transfer
SMB_BUSY = 0; // And free SMBus interface
}
break;
// Master Transmitter: Data byte transmitted. NACK received.
// Restart the transfer.
case SMB_MTDBNACK: //0x30
STA = 1; // Restart transfer
break;
// Master Receiver: Slave address + READ transmitted. ACK received.
// For a READ: check if this is a one-byte transfer. if so, set the
// NACK after the data byte is received to end the transfer. if not,
// set the ACK and receive the other data bytes.
//
// For a WRITE: N/A
case SMB_MRADDACK: //0x40
if (rec_byte_counter == NUM_BYTES_RD)
{
AA = 0; // Only one byte in this transfer,
// send NACK after byte is received
}
else
{
AA = 1; // More than one byte in this transfer,
// send ACK after byte is received
}
break;
// Master Receiver: Slave address + READ transmitted. NACK received.
// Restart the transfer.
case SMB_MRADDNACK: //0x48
STA = 1; // Restart transfer
break;
// Master Receiver: Data byte received. ACK transmitted.
// For a READ: receive each byte from the slave. if this is the last
// byte, send a NACK and set the STOP bit.
//
// For a WRITE: N/A
case SMB_MRDBACK: //0x50
if (rec_byte_counter < NUM_BYTES_RD)
{
SMB_DATA_IN[rec_byte_counter-1] = SMB0DAT; // Store received byte
AA = 1; // Send ACK to indicate byte received
rec_byte_counter++; // Increment the byte counter
}
else
{
AA = 0; // Send NACK to indicate last byte
// of this transfer
}
break;
// Master Receiver: Data byte received. NACK transmitted.
// For a READ: Read operation has completed. Read data register and
// send STOP.
//
// For a WRITE: N/A
case SMB_MRDBNACK: //0x58
SMB_DATA_IN[rec_byte_counter-1] = SMB0DAT; // Store received byte
STO = 1;
SMB_BUSY = 0;
AA = 1; // Set AA for next transfer
break;
// Master Transmitter: Arbitration lost.
case SMB_MTARBLOST: //0x38
FAIL = 1; // Indicate failed transfer
// and handle at end of ISR
break;
// All other status codes invalid. Reset communication.
default:
FAIL = 1;
break;
}
if (FAIL) // If the transfer failed,
{
SMB0CN &= ~0x40; // Reset communication
SMB0CN |= 0x40;
STA = 0;
STO = 0;
AA = 0;
SMB_BUSY = 0; // Free SMBus
FAIL = 0;
}
SI = 0; // Clear interrupt flag
}
//-----------------------------------------------------------------------------
// Support Functions
//-----------------------------------------------------------------------------
//-----------------------------------------------------------------------------
// SMB_Write
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters : None
//
// Writes a single byte to the slave with address specified by the <TARGET>
// variable.
// Calling sequence:
// 1) Write target slave address to the <TARGET> variable
// 2) Write outgoing data to the <SMB_DATA_OUT> array
// 3) Call SMB_Write()
//
void SMB_Write (void)
{
char SFRPAGE_SAVE = SFRPAGE; // Save Current SFR page
SFRPAGE = SMB0_PAGE;
while (SMB_BUSY); // Wait for SMBus to be free.
SMB_BUSY = 1; // Claim SMBus (set to busy)
SMB_RW = 0; // Mark this transfer as a WRITE
STA = 1; // Start transfer
SFRPAGE = SFRPAGE_SAVE; // Restore SFR page detector
}
//-----------------------------------------------------------------------------
// SMB_Read
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters : None
//
// Reads a single byte from the slave with address specified by the <TARGET>
// variable.
// Calling sequence:
// 1) Write target slave address to the <TARGET> variable
// 2) Call SMB_Write()
// 3) Read input data from <SMB_DATA_IN> array
//
void SMB_Read (void)
{
char SFRPAGE_SAVE = SFRPAGE; // Save Current SFR page
SFRPAGE = SMB0_PAGE;
while (SMB_BUSY); // Wait for bus to be free.
SMB_BUSY = 1; // Claim SMBus (set to busy)
SMB_RW = 1; // Mark this transfer as a READ
STA = 1; // Start transfer
while (SMB_BUSY); // Wait for transfer to complete
SFRPAGE = SFRPAGE_SAVE; // Restore SFR page detector
}
主要连续执行以下操作：发送3个字节。第一个字节是器件寄存器指针。然后读取相同的寄存器（因为指针已经设置）。它确实这样做了。
while (1)
{
TARGET = SLAVE_ADDR; // Target the Slave for next SMBus
// transfer
SMB_DATA_OUT[0] = 0x01; // Device register
SMB_DATA_OUT[1] = 0x0A; // Register MSByte
SMB_DATA_OUT[2] = 0x03; // Register LSbyte
SMB_Write(); // Initiate SMBus write
// SMBus Read Sequence
TARGET = SLAVE_ADDR; // Target the Slave for next SMBus
// transfer
SMB_Read();
}
这是一个trace capture of transfer：
在我看来，主接收器正在发送额外的ACK。所以我的主要关注点是案例：
SMB_MRADDACK：// 0x40
SMB_MRADDNACK：// 0x48
SMB_MRDBACK：// 0x50
我主要关注的是SMB_MRADDNACK：// 0x48以及它在ISR调用期间通过if语句的次数。我在确切的失败点周围缠头时遇到了一些麻烦。那么这个额外的ACK来自哪里？如果我当时没有弄明白的话，我会在星期一下午回顾这里。
奖金问题：是否存在某种嵌入式堆栈交换？在社区中没有看到任何突出的东西..
答案 0 :(得分：1)
您的跟踪显示（不包括寻址）发送的三个字节和三个字节读取。我假设您希望写入三个字节，然后只读取两个字节。如果这是真的，那么问题不仅仅是一个虚假的ACK，因为你的主机也继续计时第三个字节。
如果您希望仅使用SiLabs 1中的示例代码读取两个字节，则需要将NUM_BYTES_RD定义为2而不是提供的3.该值在{{1}中使用}和SMB_MRADDACK表示决定是ACK还是STOp。
以防万一（因为你问的是ACK而不是额外的字节），如果你的问题是关于跟踪中SDL行的最终下降（SMB_MRDBACK之后），因为你害怕＆＃39} ＃39;是一个额外的确认，然后不要担心。这是STO（在高SCL期间上升）并且是主终止传输的正确行为。
编辑：klamb在下面的评论中是正确的，SMB_MRDBACK状态存在错误。在针对0xff核对SMB0DAT之前，应该保存rec_byte_counter并递增rec_byte_counter。嘲笑那样的SiLabs。
答案 1 :(得分：0)
case SMB_MRDBACK: //0x50
SMB_DATA_IN[rec_byte_counter-1] = SMB0DAT; // Store received byte
rec_byte_counter++; // Increment the byte counter
if (rec_byte_counter < NUM_BYTES_RD)
{
AA = 1; // Send ACK to indicate byte received
}
else
{
AA = 0; // Send NACK to indicate last byte
// of this transfer
}
break;