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Please refer to section libdoc for more details on the µC/LIB module and its configuration.
Heap Memory Calculation for an Interface
The µC/LIB memory heap is used for allocation of the following objects:
- Transmit small buffers
- Transmit large buffers
- Receive large buffers
- Network Buffers (Network Buffer header and pointer to data area)
- DMA receive descriptors
- DMA transmit descriptors
- Interface data area
- Device driver data area
- OS objects (Semaphore, mutex, stack)
- ICMP Echo request objects (note that object are only allocated when the ICMP Echo request is sent, not at during the Network Protocol Stack initialization)
In the following example, the use of a Network Device Driver with DMA support is assumed. DMA descriptors are included in the analysis. The size of Network Buffer Data Areas (1, 2, 3) vary based on configuration. Refer to Chapter 9, “Buffer Management”. However, for this example, the following object sizes in bytes are assumed:
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The approximate memory heap size may be determined according to the following expressions:
| Code Block |
|---|
nbr buf per interface = nbr small Tx buf +
nbr large Tx buf +
nbr large Rx buf
nbr net buf per interface = nbr buf per interface
nbr objects = nbr buf per interface +
nbr net buf per interface +
nbr Rx descriptors +
nbr Tx descriptors +
1 Ethernet data area +
1 Device driver data area
interface mem = (nbr small Tx buf * 60) +
(nbr large Tx buf * 1518) +
(nbr large Rx buf * 1518) +
(nbr Rx descriptors * 8) +
(nbr Tx descriptors * 8) +
(Ethernet IF data area * 7) +
(Ethernet Drv data area * 108) +
(nbr objects * 3)
total mem required = nbr interfaces * interface mem
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Example
With the following configuration, the memory heap required is:
- 10 small transmit buffers
- 10 large transmit buffers
- 10 large receive buffers
- 6 receive descriptors
- 20 transmit descriptors
- Ethernet interface (interface + device driver data area required)
| Code Block | ||
|---|---|---|
| ||
nbr buf per interface = 10 + 10 + 10 = 30 nbr net buf per interface = nbr buf per interface = 30 nbr objects = (30 + 30 + 6 + 20 + 1 + 1) = 88 interface mem = (10 * 60) + (10 * 1518) + (10 * 1518) + ( 6 * 8) + (20 * 8) + ( 1 * 7) + ( 1 * 108) + (88 * 3) = 31,547 bytes total mem required > 31,547 ( + localhost memory, if enabled) |
The localhost interface, when enabled, requires a similar amount of memory except that it does not require Rx and Tx descriptors, an IF data area, or a device driver data area.
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