aLec16_localVariables - Introduction to Embedded...

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Introduction to Embedded Microcomputer Systems Lecture 16.1 Jonathan W. Valvano Recap Finite State Machines Pointer implementation Overview Fixed-point: why, when, how Local variables: scope and allocation How these concepts apply to C Binding, allocation, access, deallocation Floating point numbers ANSI/IEEE Std 754-1985 single-precision (32-bit), double-precision (64-bit), and double-extended precision (80-bits). The floating-point format Bit 31 sign, s =0 for positive, s =1 for negative Bits 30:23 8-bit biased binary exponent 0 e 255 Bits 22:0 24-bit mantissa, m expressed as a binary fraction a binary 1 as the most significant bit is implied m = 1 .m 1 m 2 m 3 ... m 23 se 7 e 0 m 1 m 23 f = (-1) s • 2 e-127 m 10.1. Fixed-point numbers Fixed point numbers Why? (wish to represent non-integer values) Next lab measures distance from 0 to 3 cm E.g., 1.234 cm When? (range is known, range is small) Range is 0 to 3cm Resolution is 0.003 cm How? (value = Integer* Δ ) 16-bit unsigned integer Δ = 10 -3 decimal fixed-point Range becomes 0.000 to 65.535 Output an integer. Assume integer, n, is between 0 and 9999. not very pretty OutChar($30+n/1000) ;thousand’s digit n = n%1000 OutChar($30+n/100) ;hundred’s digit n = n%100 OutChar($30+n/10) ;ten’s digit OutChar ($30+n%10) ;one’s digit Output a fixed-point number. Assume the integer part of the fixed point number, n, is between 0 and 9999. very pretty
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Introduction to Embedded Microcomputer Systems Lecture 16.2 Jonathan W. Valvano OutChar($30+n/1000) ;thousand’s digit n = n%1000 OutChar($2E) ;decimal point OutChar($30+n/100) ;hundred’s digit n = n%100 OutChar($30+n/10) ;ten’s digit OutChar ($30+n%10) ;one’s digit 7.3. Local Variables Introduction scope => from where can this information be accessed private means restricted to current program segment public means any software can access it allocation => when is it created, when is it destroyed dynamic allocation using registers or stack permanent allocation assigned a block of memory
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aLec16_localVariables - Introduction to Embedded...

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