Cirrus Logic CS485 Manual de usuario descargar pdf (Pagina 55)

CS485G Spring 2015 55

(b) stdio: buffering increases efﬁciency, and short counts are han-

dled automatically. But no way to read metadata, not async-

signal-safe, not a good idea to use on sockets (there are some

poorly documented restrictions).

11. Dealing with binary ﬁles (like images and object ﬁles)

(a) Don’t use line-oriented functions like fgets(), scanf(), printf(),

rio readlineb().

(b) Don’t use string-oriented functions like strlen(); data ﬁles

may contain null bytes.

55 Virtual memory

1. All memory reads and writes are implemented on two data linking

the CPU and memory.

(a) The data path is bidirectional, leading from the CPU through a

bus to the memory.

(b) The address path is unidirectional. It goes from the CPU through

a memory-management unit (MMU), which modiﬁes the ad-

dress, then to the bus to the memory.

outgoing (physical) addresses.

(d) The MMU generates a trap if the tables indicate the virtual ad-

dress is not mapped or the map does not give permission to

read/write/execute.

(e) The kernel sets up those tables, typically one for privileged mode

and one for unprivileged mode.

(f) Lecture 31, 4/17/2015

(g) Context switches don’t require reloading the tables.

(h) Process switches do require reloading the unprivileged-mode

table.

(i) The tables themselves are typically in memory, but the MMU

keeps a cache of recently-used entries; this cache is called a

translation look-aside buffer (TLB).

2. Advantages of virtual memory

1 2 ... 50 51 52 53 54 55 56 57 58 59 60 ... 66 67

Sin comentarios

Cirrus Logic CS485 Manual de usuario Pagina 55