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| 型號： | AN2821 |
| 英文描述： | eTPU Host Interface |
| 中文描述： | eTPU主機(jī)接口 |
| 文件頁數(shù)： | 7/24頁 |
| 文件大?。?/td> | 546K |
| 代理商： | AN2821 |
Host Interface Software
eTPU Host Interface, Rev. .1
Freescale Semiconductor
7
initiating the eTPU function execution by issuing a host service request. Once the host service request for
initialization is recognized, the eTPU will transition to the initialization state.
Unlike in the host CPU, the eTPU function parameters passed from host are not placed on the stack.
Instead, memory in the function frame is allocated to accommodate every function parameter. The host
passes the eTPU function parameters by writing directly to the eTPU function frame. The host needs to
know the function frame for each channel, as well as the data type and address offset for every parameter.
The function frame can be obtained by reading the eTPU channel base address register. The eTPU_C
compiler provides the host interface macros to export the offset of each function parameter; use them in
#pragma write
directives to export this information.
The function parameters can be 8-bit, 16-bit, or 32-bit. The eTPU compiler can allocate function
parameters at 8-, 16-, 24-, or 32-bit boundaries. To pass 8-bit or 16-bit parameters, the host can directly
write to eTPU data memory.
Most eTPU data registers and timers are 24-bit. To pass 24-bit eTPU function parameters, the host needs
to pass a 32-bit parameter to the eTPU. Since the host cannot access eTPU data memory on the 24-bit
boundary, the host code needs to realign the parameter to the 32-bit address boundary before writing it to
the function frame. It is the responsibility of the host to ensure the function parameters are within proper
range. It is also the responsibility of the host when writing the 24-bit parameter to ensure that the upper
byte on the function frame is not corrupted. Similarly, when reading a 24 bit return value from the function
frame, the host code must mask the upper byte before returning the correct 24 bit value. To simplify the
interface code, it is recommended to access the 24-bit function parameter by using PSE memory space. An
example of the eTPU function initialization is listed in
Code Example 7
(
etpu_pwm_init()
).
4.5
eTPU and Host Interactive Control
Once the eTPU function is initialized, it will start execution based on the initial parameters and
input/output conditions. The eTPU function can provide the API for the host application code to update
the function parameter or change the control mode. Similarly, the host software has to provide proper logic
to handle the eTPU interrupt or DMA requests.
The software to handle the host and eTPU interaction has to cross between two different compilers. When
the host initiates the eTPU function, the data flows from the host to eTPU. This behavior is the same as
the “call by value” protocol in the standard C syntax. Sometimes “call by reference” is desired to access
eTPU function internal variables. Since the data flow for “call by reference” has to cross both compilers,
it is not directly supported by the compilers. However, the behavior of the “call by reference” can be
implemented in the host interface software. The host interface software can pass a reference to the API
function to access the eTPU function internal variables. An example of the “call by reference”
implementation is shown in both
Code Example 1
and
Code Example 7
(
etpu_pwm_getStartTime()
)
Some eTPU functions require host or DMA service. The eTPU software can write the CIRC bits in the
channel interrupt and data transfer request register to send the request to the host or DMA. The interrupt
service routine must be added and the DMA channel must be configured in the host code to respond to the
eTPU request.
The host interface software has to provide functions to update eTPU function parameters or change the
control mode during the normal operation. Similar to the function initialization API, the interface API
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