STM32 FSMC總線深入研究

2. FSMC時序研究

下圖為FSMC寫命令與數據的時序圖，從中根據上圖可以分析出FSMC可以實現16M的數據寫入。FSMC的信號線翻轉非常快，這使得IC或者FPGA時序設計上得非常嚴謹。FSMC最大實現了72MHz（66.7到100MHz之間，實際為72MHz，HCLK）的翻轉速度，這要求外部器件支持那么高的速率。

寄存器配置（寄存器+數據）

連續數據寫入（0xBB：寫數據開始）,命令后，RS默認拉低（FSMC和標準不一樣的地方）

數據建立很快

寫數據，然后默認RS拉低

整體的時序可模擬為：

task task_writecmd;

input [15:0] cmd;

begin

mcu_cs = 0;

mcu_rs = 0;

mcu_data = cmd;

#20;

mcu_we = 0;

#20;

mcu_we = 1;

#15;

mcu_rs = 1;

mcu_cs = 1;

#20;

end

endtask

task task_writedata;

input [15:0] data;

begin

mcu_cs = 0;

mcu_rs = 1;

mcu_data = data;

#20;

mcu_we = 0;

#20;

mcu_we = 1;

#15;

mcu_rs = 1;

mcu_cs = 1;

#20;

end

endtask

3. FSMC接口初始化

根據手冊，相關參數如下表所示。這里我發現所謂最小值還能設置為最小，但實際速度差不多。FSMC協議時間參數如下所示：

有人跟我說，手冊是保守的；有人跟我說，在小就是默認值了。我不太理解。感覺速度每提升，應該在小就是默認了。不過，反正我追求速度的極限。

以下是FSMC-SRAM模式下的初始化代碼，分享的同時，希望對你有用。

typedefstruct{ vu16 LCD_REG; vu16 LCD_RAM; } LCD_TypeDef;#defineLCD_WriteCmd(cmd) LCD->LCD_REG = cmd#defineLCD_WriteData(data) LCD->LCD_RAM = data#defineLCD_BASE ((u32)(0x60000000 | 0x0C000000))#defineLCD ((LCD_TypeDef *) LCD_BASE)voidLCD_FSMCConfig(void) { FSMC_NORSRAMInitTypeDef FSMC_NORSRAMInitStructure; FSMC_NORSRAMTimingInitTypeDefp;//標準// p.FSMC_AddressSetupTime = 1;// p.FSMC_AddressHoldTime = 2;// p.FSMC_DataSetupTime = 2;// p.FSMC_BusTurnAroundDuration = 1;// p.FSMC_CLKDivision = 1;// p.FSMC_DataLatency = 2;//超快p.FSMC_AddressSetupTime = 0; p.FSMC_AddressHoldTime = 0; p.FSMC_DataSetupTime = 1; p.FSMC_BusTurnAroundDuration = 0; p.FSMC_CLKDivision = 0; p.FSMC_DataLatency = 0; p.FSMC_AccessMode = FSMC_AccessMode_A; FSMC_NORSRAMInitStructure.FSMC_Bank = FSMC_Bank1_NORSRAM4; FSMC_NORSRAMInitStructure.FSMC_DataAddressMux = FSMC_DataAddressMux_Disable; FSMC_NORSRAMInitStructure.FSMC_MemoryType = FSMC_MemoryType_SRAM; FSMC_NORSRAMInitStructure.FSMC_MemoryDataWidth = FSMC_MemoryDataWidth_16b; FSMC_NORSRAMInitStructure.FSMC_BurstAccessMode = FSMC_BurstAccessMode_Disable; FSMC_NORSRAMInitStructure.FSMC_WaitSignalPolarity = FSMC_WaitSignalPolarity_Low; FSMC_NORSRAMInitStructure.FSMC_WrapMode = FSMC_WrapMode_Disable; FSMC_NORSRAMInitStructure.FSMC_WaitSignalActive = FSMC_WaitSignalActive_BeforeWaitState; FSMC_NORSRAMInitStructure.FSMC_WriteOperation = FSMC_WriteOperation_Enable; FSMC_NORSRAMInitStructure.FSMC_WaitSignal = FSMC_WaitSignal_Disable; FSMC_NORSRAMInitStructure.FSMC_ExtendedMode = FSMC_ExtendedMode_Disable; FSMC_NORSRAMInitStructure.FSMC_AsynchronousWait = FSMC_AsynchronousWait_Disable;//2.0FSMC_NORSRAMInitStructure.FSMC_WriteBurst = FSMC_WriteBurst_Disable; FSMC_NORSRAMInitStructure.FSMC_ReadWriteTimingStruct = &p; FSMC_NORSRAMInitStructure.FSMC_WriteTimingStruct = &p; FSMC_NORSRAMInit(&FSMC_NORSRAMInitStructure); FSMC_NORSRAMCmd(FSMC_Bank1_NORSRAM4, ENABLE); }